/* --------------------------------------------------------------------------
 * Primitives for manipulating global data structures
 *
 * The Hugs 98 system is Copyright (c) Mark P Jones, Alastair Reid, the
 * Yale Haskell Group, and the OGI School of Science & Engineering at OHSU,
 * 1994-2003, All rights reserved.  It is distributed as free software under
 * the license in the file "License", which is included in the distribution.
 *
 * $RCSfile: storage.c,v $
 * $Revision: 1.1 $
 * $Date: 2008/11/30 09:11:37 $
 * ------------------------------------------------------------------------*/

#include "prelude.h"
#include "storage.h"
#include "connect.h"
#include "opts.h"
#include "errors.h"
#include "machdep.h"
#include "evaluator.h" /* everybody() proto only */
#include "strutil.h"
#include "output.h"	/* needed for DEBUG_PRINTER|PROFILING */
#include <setjmp.h>

/*#define DEBUG_SHOWUSE*/

/* --------------------------------------------------------------------------
 * local function prototypes:
 * ------------------------------------------------------------------------*/

static Int  local hash                  Args((String));
static Int  local saveText              Args((Text));
static Void local hashTycon             Args((Tycon));
static List local insertTycon           Args((Tycon,List));
static Void local hashName              Args((Name));
static List local insertName            Args((Name,List));
static Void local patternError          Args((String));
static Bool local stringMatch           Args((String,String));
static Bool local typeInvolves		Args((Type,Type));
static Cell local markCell              Args((Cell));
static Cell local markSnd               Args((Cell));
static Cell local indirectChain         Args((Cell));
static Bool local isMarked		Args((Cell));
static Cell local lowLevelLastIn        Args((Cell));
static Cell local lowLevelLastOut       Args((Cell));
#if IO_HANDLES
static Void local freeHandle            Args((Int));
#endif
#if GC_STABLEPTRS
static Void local resetStablePtrs       Args((Void));
#endif
#if OBSERVATIONS
static Observe  local newObserve        Args((Text));
static Void     local appendObs         Args((Cell,Cell));
static Breakpt  local addBreakpt        Args((String));
static Breakpt  local findBreakpt       Args((String));
#endif


/* --------------------------------------------------------------------------
 * Text storage:
 *
 * provides storage for the characters making up identifier and symbol
 * names, string literals, character constants etc...
 *
 * All character strings are stored in a large character array, with textHw
 * pointing to the next free position.  Lookup in the array is improved using
 * a hash table.  Internally, text strings are represented by integer offsets
 * from the beginning of the array to the string in question.
 *
 * Where memory permits, the use of multiple hashtables gives a significant
 * increase in performance, particularly when large source files are used.
 *
 * Each string in the array is terminated by a zero byte.  No string is
 * stored more than once, so that it is safe to test equality of strings by
 * comparing the corresponding offsets.
 *
 * Special text values (beyond the range of the text array table) are used
 * to generate unique `new variable names' as required.
 *
 * The same text storage is also used to hold text values stored in a saved
 * expression.  This grows downwards from the top of the text table (and is
 * not included in the hash table).
 * ------------------------------------------------------------------------*/

#define TEXTHSZ 512                     /* Size of Text hash table         */
#define NOTEXT  ((Text)(~0))            /* Empty bucket in Text hash table */
static  Text    textHw;                 /* Next unused position            */
static  Text    savedText = NUM_TEXT;   /* Start of saved portion of text  */
static  Text    nextNewText;            /* Next new text value             */
static  Text    nextNewDText;           /* Next new dict text value        */
static  char    DEFTABLE(text,NUM_TEXT);/* Storage of character strings    */
static  Text    textHash[TEXTHSZ][NUM_TEXTH]; /* Hash table storage        */

String textToStr(t)                    /* find string corresp to given Text*/
Text t; {
    static char newVar[16];

    if (0<=t && t<NUM_TEXT)                     /* standard char string    */
	return text + t;
    if (t<0)
	sprintf(newVar,"d%d",-t);               /* dictionary variable     */
    else
	sprintf(newVar,"v%d",t-NUM_TEXT);       /* normal variable         */
    return newVar;
}

String identToStr(v) /*find string corresp to given ident or qualified name*/
Cell v; {
    if (!isPair(v)) {
	internal("identToStr");
    }
    switch (fst(v)) {
	case VARIDCELL  :
	case VAROPCELL  : 
	case CONIDCELL  :
	case CONOPCELL  : return text+textOf(v);

	case QUALIDENT  : {   Text pos = textHw;
			      Text t   = qmodOf(v);
			      while (pos+1 < savedText && text[t]!=0) {
				  text[pos++] = text[t++];
			      }
			      if (pos+1 < savedText) {
				  text[pos++] = '.';
			      }
			      t = qtextOf(v);
			      while (pos+1 < savedText && text[t]!=0) {
				  text[pos++] = text[t++];
			      }
			      text[pos] = '\0';
			      return text+textHw;
			  }
    }
    internal("identToStr2");
    return 0;/*NOTUSED*/
}

Text inventText()     {                 /* return new unused variable name */
    return nextNewText++;
}

Text inventDictText() {                 /* return new unused dictvar name  */
    return nextNewDText--;
}

Bool inventedText(t)                    /* Signal TRUE if text has been    */
Text t; {                               /* generated internally            */
    return (t<0 || t>=NUM_TEXT);
}

#define MAX_FIXLIT 100
Text fixLitText(t)                /* fix literal text that might include \ */
Text t; {
    String   s = textToStr(t);
    char     p[MAX_FIXLIT];
    Int      i;
    for(i = 0;i < MAX_FIXLIT-2 && *s;s++) {
      p[i++] = *s;
      if (*s == '\\') {
	p[i++] = '\\';
      } 
    }
    if (i < MAX_FIXLIT-2) {
      p[i] = 0;
    } else {
	ERRMSG(0) "storage space exhausted for internal literal string"
	EEND;
    }
    return (findText(p));
}
#undef MAX_FIXLIT

#define MAX_TEXTLEN 4000 /* cf. MAX_TOKEN in input.c */
Text concatText(s1,s2)
String s1;
String s2; {
    char s[MAX_TEXTLEN];

    if (snprintf(s,MAX_TEXTLEN,"%s%s",s1,s2) == -1) {
	ERRMSG(0) "Generated name '%s%s' exceeds limit of %d",
                  s1, s2, MAX_TEXTLEN
	EEND;
    }
    return findText(s);
}    
#undef MAX_TEXTLEN

Text subText(s,l)                /* extract a substring and make it a Text */
String s;
Int    l; {
    /* 
     * This used to insert '\0' at s[l], do a lookup and then change s[l]
     * back to its old value.  This fails if the String happens to be the
     * result of textToStr so instead we make a copy, do the lookup and 
     * forget the copy.
     */
    String t = strnCopy(s, l);
    Text r = findText(t);
    free(t);
    return r;
}

static Int local hash(s)                /* Simple hash function on strings */
String s; {
    int v, j = 3;

    for (v=((int)(*s))*8; *s; s++)
	v += ((int)(*s))*(j++);
    if (v<0)
	v = (-v);
    return(v%TEXTHSZ);
}

Text findText(s)                       /* Locate string in Text array      */
String s; {
    int    h       = hash(s);
    int    hashno  = 0;
    Text   textPos = textHash[h][hashno];

#define TryMatch        {   Text   originalTextPos = textPos;              \
			    String t;                                      \
			    for (t=s; *t==text[textPos]; textPos++,t++)    \
				if (*t=='\0')                              \
				    return originalTextPos;                \
			}
#define Skip            while (text[textPos++]) ;

    while (textPos!=NOTEXT) {
	TryMatch
	if (++hashno<NUM_TEXTH)         /* look in next hashtable entry    */
	    textPos = textHash[h][hashno];
	else {
	    Skip
	    while (textPos < textHw) {
		TryMatch
		Skip
	    }
	    break;
	}
    }

#undef TryMatch
#undef Skip

    textPos = textHw;                  /* if not found, save in array      */
    if (textHw + (Int)strlen(s) + 1 > savedText) {
	ERRMSG(0) "Character string storage space exhausted"
	EEND;
    }
    while ((text[textHw++] = *s++) != 0) {
    }
    if (hashno<NUM_TEXTH) {            /* updating hash table as necessary */
	textHash[h][hashno] = textPos;
	if (hashno<NUM_TEXTH-1)
	    textHash[h][hashno+1] = NOTEXT;
    }

    return textPos;
}

static Int local saveText(t)            /* Save text value in buffer       */
Text t; {                               /* at top of text table            */
    String s = textToStr(t);
    Int    l = strlen(s);

    if (textHw + l + 1 > savedText) {
	ERRMSG(0) "Character string storage space exhausted"
	EEND;
    }
    savedText -= l+1;
    strcpy(text+savedText,s);
    return savedText;
}

/* --------------------------------------------------------------------------
 * Addr storage: records `next unused program location'
 * ------------------------------------------------------------------------*/

static Addr addrHw;                    /* next unused program location     */

Addr getMem(n)                         /* Get some more memory             */
Int n; {
    Addr newAddr = addrHw;
    addrHw += n;
#if WANT_FIXED_SIZE_TABLES
    if (addrHw>=NUM_ADDRS) {
	ERRMSG(0) "Program code storage space exhausted"
	EEND;
    }
#else
    while (addrHw>=(Int)(dynMemory->maxIdx)) {
	growMemory();
    }
#endif
    return newAddr;
}

Void nextInstr(a)                       /* Reset point to next instruction */
Addr a; {                               /* Currently does NO CHECKING      */
    addrHw = a;
}

/* --------------------------------------------------------------------------
 * Tycon storage:
 *
 * A Tycon represents a user defined type constructor.  Tycons are indexed
 * by Text values ... a very simple hash function is used to improve lookup
 * times.  Tycon entries with the same hash code are chained together, with
 * the most recent entry at the front of the list.
 * ------------------------------------------------------------------------*/

#define TYCONHSZ 256                            /* Size of Tycon hash table*/
#define tHash(x) ((x)%TYCONHSZ)                 /* Tycon hash function     */
static  Tycon    tyconHw;                       /* next unused Tycon       */
static  Tycon    DEFTABLE(tyconHash,TYCONHSZ);  /* Hash table storage      */
struct  strTycon DEFTABLE(tabTycon,NUM_TYCON);  /* Tycon storage           */

Tycon newTycon(t)                       /* add new tycon to tycon table    */
Text t; {
    Int h = tHash(t);

    if (tyconHw-TYCMIN >= NUM_TYCON) {
	ERRMSG(0) "Type constructor storage space exhausted"
	EEND;
    }
    tycon(tyconHw).text          = t;   /* clear new tycon record          */
    tycon(tyconHw).mod           = currentModule;
    tycon(tyconHw).kind          = NIL;
    tycon(tyconHw).what          = NIL;
    tycon(tyconHw).defn          = NIL;
    module(currentModule).tycons = cons(tyconHw,module(currentModule).tycons);
    tycon(tyconHw).nextTyconHash = tyconHash[h];
    tycon(tyconHw).clashes       = NIL;
    tyconHash[h]                 = tyconHw;

    return tyconHw++;
}

Tycon findTycon(t)                      /* locate Tycon in tycon table     */
Text t; {
    Tycon tc = tyconHash[tHash(t)];

    while (nonNull(tc) && tycon(tc).text!=t)
	tc = tycon(tc).nextTyconHash;
    return tc;
}

Tycon addTycon(tc)  /* Insert Tycon in tycon table - if no clash is caused */
Tycon tc; {
    Tycon oldtc = findTycon(tycon(tc).text);
    if (isNull(oldtc)) {
	hashTycon(tc);
	module(currentModule).tycons=cons(tc,module(currentModule).tycons);
	return tc;
    } else
	return oldtc;
}

static Void local hashTycon(tc)         /* Insert Tycon into hash table    */
Tycon tc; {
    Text  t = tycon(tc).text;
    Int   h = tHash(t);
    tycon(tc).nextTyconHash = tyconHash[h];
    tycon(tc).clashes       = NIL;
    tyconHash[h]            = tc;
}

Tycon findQualTycon(id) /*locate (possibly qualified) Tycon in tycon table */
Cell id; {
    if (!isPair(id)) internal("findQualTycon");
    switch (fst(id)) {
	case CONIDCELL :
	case CONOPCELL :
	    return findTycon(textOf(id));
	case QUALIDENT : {
	    Text   t  = qtextOf(id);
	    List   ms = findQualifiers(qmodOf(id));
	    if (isNull(ms)) return NIL;
	    while (nonNull(ms)) {
	      Module m  = hd(ms);
	      List   es = NIL;
	      ms = tl(ms);
	      if (m == currentModule) {
		es = module(m).tycons;
	      } else {
		es = getModuleImports(m);
	      }
	      for(; nonNull(es); es=tl(es)) {
		Cell e = hd(es);
		if (isTycon(e) && tycon(e).text==t) 
		  return e;
		if (isPair(e) && isTycon(fst(e)) &&  tycon(fst(e)).text==t) 
		  return fst(e);
	      }
	    }
	    return NIL;
	}
	default : internal("findQualTycon2");
    }
    return NIL;/*NOTUSED*/
}

Tycon addPrimTycon(t,kind,ar,what,defn) /* add new primitive type constr   */
Text t;
Kind kind;
Int  ar;
Cell what;
Cell defn; {
    Tycon tc        = newTycon(t);
    tycon(tc).line  = 0;
    tycon(tc).kind  = kind;
    tycon(tc).what  = what;
    tycon(tc).defn  = defn;
    tycon(tc).arity = ar;
    tycon(tc).mod    = currentModule;

    return tc;
}

static List local insertTycon(tc,ts)    /* insert tycon tc into sorted list*/
Tycon tc;                               /* ts                              */
List  ts; {
    Cell   prev = NIL;
    Cell   curr = ts;
    String s    = textToStr(tycon(tc).text);

    while (nonNull(curr) && strCompare(s,textToStr(tycon(hd(curr)).text))>=0) {
	if (hd(curr)==tc)               /* just in case we get duplicates! */
	    return ts;
	prev = curr;
	curr = tl(curr);
    }
    if (nonNull(prev)) {
	tl(prev) = cons(tc,curr);
	return ts;
    }
    else
	return cons(tc,curr);
}

List addTyconsMatching(pat,ts)          /* Add tycons matching pattern pat */
String pat;                             /* to list of Tycons ts            */
List   ts; {                            /* Null pattern matches every tycon*/
    Tycon tc;				/* (Tycons with NIL kind excluded) */
    for (tc=TYCMIN; tc<tyconHw; ++tc)
	if (!pat || stringMatch(pat,textToStr(tycon(tc).text)))
	    if (nonNull(tycon(tc).kind))
		ts = insertTycon(tc,ts);
    return ts;
}

/*
 * Remove 'tc' from a module's 'tycons' list; used to implement 
 * local overrides of imported decls.
 */
Void removeTycon(tc)
Tycon tc; {
  List ls    = module(currentModule).tycons;
  List* prev = &(module(currentModule).tycons);
    
  for (;nonNull(ls);ls=tl(ls)) {
    if (hd(ls) == tc) {
      *prev = tl(ls);
      break;
    }
    prev = &(tl(ls));
  }
}

/* --------------------------------------------------------------------------
 * Name storage:
 *
 * A Name represents a top level binding of a value to an identifier.
 * Such values may be a constructor function, a member function in a
 * class, a user-defined or primitive value/function.
 *
 * Names are indexed by Text values ... a very simple hash functions speeds
 * access to the table of Names and Name entries with the same hash value
 * are chained together, with the most recent entry at the front of the
 * list.
 * ------------------------------------------------------------------------*/

#define NAMEHSZ  256                            /* Size of Name hash table */
#define nHash(x) ((x)%NAMEHSZ)                  /* hash fn :: Text->Int    */
static  Name     nameHw;                        /* next unused name        */
static  Name     DEFTABLE(nameHash,NAMEHSZ);    /* Hash table storage      */
struct  strName  DEFTABLE(tabName,NUM_NAME);    /* Name table storage      */

Name newName(t,parent)                  /* Add new name to name table      */
Text t; 
Cell parent; {
    Int h = nHash(t);

    if (nameHw-NAMEMIN >= NUM_NAME) {
	ERRMSG(0) "Name storage space exhausted"
	EEND;
    }
    name(nameHw).text         = t;      /* clear new name record           */
    name(nameHw).line         = 0;
    name(nameHw).syntax	      = (unsigned int)NO_SYNTAX;
    name(nameHw).parent       = parent;
    name(nameHw).arity        = 0;
    name(nameHw).number       = EXECNAME;
    name(nameHw).defn         = NIL;
    name(nameHw).type         = NIL;
    name(nameHw).extFun       = 0;
    name(nameHw).foreignId    = -1; 
    name(nameHw).foreignFlags = FFI_NOSAFETY | FFI_CCONV_UNKNOWN;
    name(nameHw).primDef      = 0;
    name(nameHw).code         = 0;
    name(nameHw).mod          = currentModule;
    name(nameHw).clashes      = NIL;

    module(currentModule).names=cons(nameHw,module(currentModule).names);
    name(nameHw).nextNameHash = nameHash[h];
    nameHash[h]               = nameHw;
    return nameHw++;
}

Name findName(t)                        /* Locate name in name table       */
Text t; {
    Name n = nameHash[nHash(t)];

    while (nonNull(n) && name(n).text!=t)
      n = name(n).nextNameHash;
    return n;
}

Name addName(nm)			/* Insert Name in name table - if  */
Name nm; {				/* no clash is caused		   */
    Name oldnm = findName(name(nm).text);
    if (isNull(oldnm)) {
	hashName(nm);
	module(currentModule).names=cons(nm,module(currentModule).names);
	return nm;
    } else
	return oldnm;
}

static Void local hashName(nm)          /* Insert Name into hash table	   */
Name nm; {
    Text t		  = name(nm).text;
    Int  h		  = nHash(t);

    name(nm).nextNameHash = nameHash[h];
    name(nm).clashes      = NIL;
    nameHash[h]           = nm;
}

/*
 * Remove 'n' from a module's 'names' list; used to implement 
 * local overrides of imported decls.
 */
Void removeName(n)
Name n; {
    List ls   = module(currentModule).names;
    List* prev = &(module(currentModule).names);
    
    for (;nonNull(ls);ls=tl(ls)) {
	if (hd(ls) == n) {
	    *prev = tl(ls);
	    break;
	}
	prev = &(tl(ls));
    }
}

Name findQualName(id)			/* Locate (possibly qualified) name*/
Cell id; {				/* in name table		   */
    if (!isPair(id))
	internal("findQualName");
    switch (fst(id)) {
	case VARIDCELL :
	case VAROPCELL :
	case CONIDCELL :
	case CONOPCELL :
	    return findName(textOf(id));
	case QUALIDENT : {
	    Text   t  = qtextOf(id);
	    List  ms  = findQualifiers(qmodOf(id));
	    if (isNull(ms)) return NIL;
	    while (nonNull(ms)) {
	      Module m  = hd(ms);
	      List   es = NIL;
	      ms = tl(ms);
	      if (m == currentModule) {
		es = module(m).names;
	      } else {
		es = getModuleImports(m);
	      }
	      for(; nonNull(es); es=tl(es)) {
		Cell e = hd(es);
		if (isName(e) && name(e).text==t) 
		    return e;
		if (isTycon(e) && tycon(e).text==t) 
		    return e;
		else if (isPair(e)) {
		    List subentities = NIL;
		    Cell c = fst(e);
		    if (snd(e) == DOTDOT) {
			if (isTycon(c)
			    && (tycon(c).what==DATATYPE || tycon(c).what==NEWTYPE)) {
			    subentities = tycon(c).defn;
			} else if (isClass(c))
			    subentities = cclass(c).members;
		    } else {
			subentities = snd(e);
		    }
		    for(; nonNull(subentities); subentities=tl(subentities)) {
			if (name(hd(subentities)).text == t)
			    return hd(subentities);
		    }
		}
	      }
	    }
	    return NIL;
	}
	default : internal("findQualName2");
    }
    return NIL;/*NOTUSED*/
}

List findQualNames(id)			/* Locate (possibly qualified) names */
Cell id; {				/* in name table		     */
    if (!isPair(id))
	internal("findQualNames");
    switch (fst(id)) {
	case VARIDCELL :
	case VAROPCELL :
	case CONIDCELL :
	case CONOPCELL :
  	    return singleton(findName(textOf(id)));
	case QUALIDENT : {
	    Text  t        = qtextOf(id);
	    Text  aliasMod = qmodOf(id);
	    List  ms       = findQualifiers(aliasMod);
	    List res       = NIL;
	    Bool fromHome  = FALSE;
	    if (isNull(ms)) return NIL;
	    while (nonNull(ms)) {
	      Module m  = hd(ms);
	      List   es = NIL;
	      ms = tl(ms);
	      /* For each module with alias 'aliasMod', get at
	       * what 'currentModule' imports from it.
	       */
	      if (m == currentModule) {
		es = module(m).names;
		fromHome = TRUE;
	      } else {
		es = getModuleImports(m);
		fromHome = FALSE;
	      }
	      /* Chase down list looking for _unqual_ entity. */
	      for(; nonNull(es); es=tl(es)) {
		Cell e = hd(es);
		if (isName(e) && name(e).text==t 
		    && !cellIsMember(e,res)) {
		    if (fromHome && name(e).mod != currentModule) {
		      /* If we're processing local names, only interested in
		       * names that were actually declared there.
		       */
			continue;
		    }
		    res = cons(e,res);
		} else if (isPair(e)) {
		    List subentities = NIL;
		    Cell c = fst(e);
		    if (DOTDOT==snd(e)) {
			if (isTycon(c)
			    && (tycon(c).what==DATATYPE || tycon(c).what==NEWTYPE))
			    subentities = tycon(c).defn;
			else if (isClass(c))
			    subentities = cclass(c).members;
		    } else {
			subentities = snd(e);
		    }
		    for(; nonNull(subentities); subentities=tl(subentities)) {
			if (name(hd(subentities)).text == t
			    && !cellIsMember(hd(subentities),res) ) {
			    if (fromHome && name(hd(subentities)).mod != currentModule) {
				continue;
			    }
			    res=cons(hd(subentities),res);
			}
		    }
		}
	      }
	    }
	    return res;
	}
	default : internal("findQualName2");
    }
    return NIL;/*NOTUSED*/
}



Name findQualFun(m,v)                  /* Locate name in name table       */
Text m;
Text v; {
    Module mod = findModule(m);
    List ns;
    if (isNull(mod)) {
        return NIL;
    }
    for(ns=module(mod).names; nonNull(ns); ns=tl(ns)) {
        Name n = hd(ns);
        if (name(n).text == v) {
            return n;
        }
    }
    return NIL;
}

/* --------------------------------------------------------------------------
 * Primitive functions:
 * ------------------------------------------------------------------------*/

struct primInfoDef {
    Module              prim_module; /* module that defined prim-table */
    struct primInfo*    p_info;
    struct primInfoDef* nextPrimInfoDef; /* subsumes nextPrimInfo (ToDo: nuke it) */
};

static Void local freePrimInfo Args((struct primInfoDef*));

static struct primInfoDef *firstPrimInfo = 0; /* queue of primInfo structures */
static struct primInfoDef *lastPrimInfo  = 0;


Void registerPrims(info)                /* register new primitives         */
struct primInfo *info; {
    struct primInfoDef* new_entry;
    /* ToDo: this is in all likelihood not the Approved Way of asking for mem. from the OS.
     *       Figure out what's the local idiom.      
     */
    if ( (new_entry = malloc(sizeof(struct primInfoDef))) == NULL ) {
	/* It's going to break pretty soon anyway...*/
       return;
    } else {
       new_entry->prim_module = currentModule;
       new_entry->p_info      = info;
    }
    if (0 == firstPrimInfo)		/* first entry in queue		   */
	firstPrimInfo = lastPrimInfo = new_entry;
    else
	lastPrimInfo = lastPrimInfo->nextPrimInfoDef = new_entry;

    lastPrimInfo->nextPrimInfoDef = 0;
}


static Void local freePrimInfo(p)
struct primInfoDef* p; {
  struct primInfoDef* info = firstPrimInfo;
  struct primInfoDef* prev = 0;

  while (info) {
    if (info == p) {
      /* Remove it from the list */
      if (prev) {
	prev->nextPrimInfoDef = info->nextPrimInfoDef;
      } else {
	firstPrimInfo = info->nextPrimInfoDef;
	prev = firstPrimInfo;
      }
      if (lastPrimInfo == info) {
	lastPrimInfo = prev;
      }
      free(p);
      return;
    }
    prev = info;
    info = info->nextPrimInfoDef;
  }
}

Void addPrim(l,n,s,mod,ty)               /* Add primitive function value    */
Int    l;
Name   n;
String s;
Module mod;
Type   ty; {
    struct primInfoDef *info_def;
    Bool lookInPrelude           = TRUE;
    name(n).line	         = l;
    name(n).defn	         = NIL;
    name(n).type	         = ty;
    name(n).mod = mod;

    /*
     * (mini) sigh - the primitives for the Prelude'ish modules
     * are special in the sense that each such module doesn't
     * have its own prim-table (cf. Int). So, we make two passes
     * over the prim-table list, first time around we demand
     * that the defining Module for the primitive we're adding
     * matches that of the Module pinned onto the prim-table we're
     * currently looking at. If that didn't produce any matches,
     * we have another go, this time scanning through the misc
     * builtin prim-tables.
     *
     * => If a module's prim-table doesn't have an entry for
     *    the prim-decl in question, we try to fall back on
     *    any of the builtin ones. 
     *
     */
    do {
      info_def       = firstPrimInfo;
      lookInPrelude  = !lookInPrelude;
      for(; 0 != info_def; info_def=info_def->nextPrimInfoDef) {
        if ( ( lookInPrelude && isPrelude(info_def->prim_module)) ||
	     mod == info_def->prim_module ) {
  	   struct primitive *prims = info_def->p_info->primFuns;
	   Int i = 0;
	   for (; prims[i].ref; ++i)
	       if (strcmp(s,prims[i].ref)==0) {
		   name(n).arity   = prims[i].arity;
		   name(n).number  = EXECNAME;
		   name(n).primDef = prims[i].imp;
		   return;
	       }
	}
      }
    } while (!lookInPrelude);

    ERRMSG(name(n).line) "Unknown primitive reference \"%s\"", s
    EEND;
}

Name addPrimCfun(t,arity,no,type)       /* add primitive constructor func  */
Text t;
Int  arity;
Int  no;
Cell type; {
    Name n         = newName(t,NIL);
    name(n).arity  = arity;
    name(n).number = cfunNo(no);
    name(n).type   = type;
    name(n).mod   = currentModule;

    return n;
}

Int sfunPos(s,c)                        /* Find position of field with     */
Name s;                                 /* selector s in constructor c.    */
Name c; {
    List cns;
    cns = name(s).defn;
    for (; nonNull(cns); cns=tl(cns))
	if (fst(hd(cns))==c)
	    return intOf(snd(hd(cns)));
    internal("sfunPos");
    return 0;/*NOTREACHED*/
}

static List local insertName(nm,ns)     /* insert name nm into sorted list */
Name nm;                                /* ns                              */
List ns; {
    Cell   prev = NIL;
    Cell   curr = ns;
    String s    = textToStr(name(nm).text);

    while (nonNull(curr) && strCompare(s,textToStr(name(hd(curr)).text))>=0) {
	if (hd(curr)==nm)               /* just in case we get duplicates! */
	    return ns;
	prev = curr;
	curr = tl(curr);
    }
    if (nonNull(prev)) {
	tl(prev) = cons(nm,curr);
	return ns;
    }
    else
	return cons(nm,curr);
}

List addNamesMatching(pat,ns)           /* Add names matching pattern pat  */
String pat;                             /* to list of names ns             */
List   ns; {                            /* Null pattern matches every name */
    Name nm;				/* (Names with NIL type, or hidden */
#if 1
    for (nm=NAMEMIN; nm<nameHw; ++nm)	/* or invented names are excluded) */
	if (!inventedText(name(nm).text) && nonNull(name(nm).type)) {
	    String str = textToStr(name(nm).text);
	    if (str[0]!='_' && (!pat || stringMatch(pat,str)))
		ns = insertName(nm,ns);
	}
    return ns;
#else
    List mns = module(currentModule).names;
    for(; nonNull(mns); mns=tl(mns)) {
	Name nm = hd(mns);
	if (!inventedText(name(nm).text)) {
	    String str = textToStr(name(nm).text);
	    if (str[0]!='_' && (!pat || stringMatch(pat,str)))
		ns = insertName(nm,ns);
	}
    }
    return ns;
#endif
}

/* --------------------------------------------------------------------------
 * A simple string matching routine
 *     `*'    matches any sequence of zero or more characters
 *     `?'    matches any single character exactly 
 *     `@str' matches the string str exactly (ignoring any special chars)
 *     `\c'   matches the character c only (ignoring special chars)
 *     c      matches the character c only
 * ------------------------------------------------------------------------*/

static Void local patternError(s)       /* report error in pattern         */
String s; {
    ERRMSG(0) "%s in pattern", s
    EEND;
}

static Bool local stringMatch(pat,str)  /* match string against pattern    */
String pat;
String str; {

    for (;;)
	switch (*pat) {
	    case '\0' : return (*str=='\0');

	    case '*'  : do {
			    if (stringMatch(pat+1,str))
				return TRUE;
			} while (*str++);
			return FALSE;

	    case '?'  : if (*str++=='\0')
			    return FALSE;
			pat++;
			break;

	    case '['  : {   Bool found = FALSE;
			    while (*++pat!='\0' && *pat!=']')
				if (!found && ( pat[0] == *str  ||
					       (pat[1] == '-'   &&
						pat[2] != ']'   &&
						pat[2] != '\0'  &&
						pat[0] <= *str  &&
						pat[2] >= *str)))

				    found = TRUE;
			    if (*pat != ']')
				patternError("missing `]'");
			    if (!found)
				return FALSE;
			    pat++;
			    str++;
			}
			break;

	    case '\\' : if (*++pat == '\0')
			    patternError("extra trailing `\\'");
			/*fallthru!*/
	    default   : if (*pat++ != *str++)
			    return FALSE;
			break;
	}
}

/* --------------------------------------------------------------------------
 * Storage of type classes, instances etc...:
 * ------------------------------------------------------------------------*/

static Class classHw;                  /* next unused class                */
static List  classes;                  /* list of classes in current scope */
static Inst  instHw;                   /* next unused instance record      */

#if WANT_FIXED_SIZE_TABLES
struct strClass DEFTABLE(tabClass,NUM_CLASSES); /* table of class records  */
#else
/* (Dynamically) growable tables holding the class and instance info */
static DynTable* dynTabClass = NULL;
static DynTable* dynTabInst = NULL;

struct strClass *tabClass;
#endif
struct strInst  *tabInst;           /* (pointer to) table of instances  */


Class newClass(t)                      /* add new class to class table     */
Text t; {
#if WANT_FIXED_SIZE_TABLES
    if (classHw-CLASSMIN >= NUM_CLASSES) {
	ERRMSG(0) "Class storage space exhausted"
	EEND;
    }
#else
    if (classHw-CLASSMIN >= (Int)(dynTabClass->maxIdx)) {
      growDynTable(dynTabClass);
      tabClass = (struct strClass*)(dynTabClass->data);
    }
#endif

    cclass(classHw).text       = t;
    cclass(classHw).line       = 0;
    cclass(classHw).arity      = 0;
    cclass(classHw).tyvars     = NIL;
    cclass(classHw).kinds      = NIL;
    cclass(classHw).head       = NIL;
    cclass(classHw).fds        = NIL;
    cclass(classHw).xfds       = NIL;
    cclass(classHw).dcon       = NIL;
    cclass(classHw).supers     = NIL;
    cclass(classHw).numSupers  = 0;
    cclass(classHw).dsels      = NIL;
    cclass(classHw).members    = NIL;
    cclass(classHw).numMembers = 0;
    cclass(classHw).defaults   = NIL;
    cclass(classHw).instances  = NIL;
    cclass(classHw).clashes    = NIL;
    classes=cons(classHw,classes);
    cclass(classHw).mod       = currentModule;
    module(currentModule).classes=cons(classHw,module(currentModule).classes);

    return classHw++;
}

Class classMax() {                      /* Return max Class in use ...     */
    return classHw;                     /* This is a bit ugly, but it's not*/
}                                       /* worth a lot of effort right now */

Class findClass(t)                     /* look for named class in table    */
Text t; {
    Class cl;
    List cs;
    for (cs=classes; nonNull(cs); cs=tl(cs)) {
	cl=hd(cs);
	if (cclass(cl).text==t)
	    return cl;
    }
    return NIL;
}

Class addClass(c)			/* Insert Class in class list	   */
Class c; {				/*  - if no clash caused	   */
    Class oldc = findClass(cclass(c).text);
    if (isNull(oldc)) {
	classes=cons(c,classes);
	module(currentModule).classes=cons(c,module(currentModule).classes);
	return c;
    }
    else
	return oldc;
}

Class findQualClass(c)			/* Look for (possibly qualified)   */
Cell c; {				/* class in class list		   */
    if (!isQualIdent(c)) {
	return findClass(textOf(c));
    } else {
	Text   t  = qtextOf(c);
	List   ms = findQualifiers(qmodOf(c));
	if (isNull(ms)) return NIL;
	while (nonNull(ms)) {
	  Module m  = hd(ms);
	  List   es = NIL;
	  ms        = tl(ms);
	  if (m == currentModule) {
	    es = module(m).classes;
	  } else {
	    es = getModuleImports(m);
	  }
	  for (; nonNull(es); es=tl(es)) {
	    Cell e = hd(es);
	    if (isClass(e) && cclass(e).text == t)
	      return e;
	    if (isPair(e) && isClass(fst(e)) && cclass(fst(e)).text==t) 
	      return fst(e);
	  }
	}
    }
    return NIL;
}

Inst newInst() {                       /* Add new instance to table        */
#if WANT_FIXED_SIZE_TABLES
    if (instHw-INSTMIN >= NUM_INSTS) {
	ERRMSG(0) "Instance storage space exhausted"
	EEND;
    }
#else
    if (instHw-INSTMIN >= (Int)(dynTabInst->maxIdx)) {
        growDynTable(dynTabInst);
	tabInst = (struct strInst*)(dynTabInst->data);
    }
#endif
    inst(instHw).kinds	    = NIL;
    inst(instHw).head	    = NIL;
    inst(instHw).specifics  = NIL;
    inst(instHw).implements = NIL;
    inst(instHw).builder    = NIL;

    return instHw++;
}

#if DEBUG_DICTS
extern Void printInst Args((Inst));

Void printInst(in)
Inst in; {
    Class cl = inst(in).c;
    Printf("%s-", textToStr(cclass(cl).text));
    printType(stdout,inst(in).t);
}
#endif /* DEBUG_DICTS */

Inst findFirstInst(tc)                  /* look for 1st instance involving */
Tycon tc; {                             /* the type constructor tc         */
    return findNextInst(tc,INSTMIN-1);
}

Inst findNextInst(tc,in)                /* look for next instance involving*/
Tycon tc;                               /* the type constructor tc         */
Inst  in; {                             /* starting after instance in      */
    while (++in < instHw) {
	Cell pi = inst(in).head;
	for (; isAp(pi); pi=fun(pi))
	    if (typeInvolves(arg(pi),tc))
		return in;
    }
    return NIL;
}

static Bool local typeInvolves(ty,tc)	/* Test to see if type ty involves */
Type ty;				/* type constructor/tuple tc.	   */
Type tc; {
    return (ty==tc)
	|| (isAp(ty) && (typeInvolves(fun(ty),tc)
			 || typeInvolves(arg(ty),tc)));
}

/* --------------------------------------------------------------------------
 * Control stack:
 *
 * Various parts of the system use a stack of cells.  Most of the stack
 * operations are defined as macros, expanded inline.
 * ------------------------------------------------------------------------*/

Cell DEFTABLE(cellStack,NUM_STACK); /* Storage for cells on stack          */
#ifndef  GLOBALsp
StackPtr sp;                        /* stack pointer                       */
#endif

#if GIMME_STACK_DUMPS

#define UPPER_DISP  5               /* # display entries on top of stack   */
#define LOWER_DISP  5               /* # display entries on bottom of stack*/

extern Int  rootsp;
extern Cell evalRoots[];

Void hugsStackOverflow() {	    /* Report stack overflow               */
    ERRMSG(0) "Control stack overflow" ETHEN
    if (rootsp>=0) {
	Int i;
	if (rootsp>=UPPER_DISP+LOWER_DISP) {
	    for (i=0; i<UPPER_DISP; i++) {
		ERRTEXT "\nwhile evaluating: " ETHEN
		ERREXPR(evalRoots[rootsp-i]);
	    }
	    ERRTEXT "\n..." ETHEN
	    for (i=LOWER_DISP-1; i>=0; i--) {
		ERRTEXT "\nwhile evaluating: " ETHEN
		ERREXPR(evalRoots[i]);
	    }
	}
	else {
	    for (i=rootsp; i>=0; i--) {
		ERRTEXT "\nwhile evaluating: " ETHEN
		ERREXPR(evalRoots[i]);
	    }
	}
    }
    ERRTEXT "\n"
    EEND;
}

#else /* !GIMME_STACK_DUMPS */

Void hugsStackOverflow() {          /* Report stack overflow               */
    ERRMSG(0) "Control stack overflow"
    EEND;
}

#endif /* !GIMME_STACK_DUMPS */

/* --------------------------------------------------------------------------
 * Observation storage
 * ------------------------------------------------------------------------*/

#if OBSERVATIONS
static Observe observeHw;                            /* next unused Observe  */
struct strObserve DEFTABLE(tabObserve,NUM_OBS_TAGS); /* Observe storage      */
static Observe currentObs;			     /* for table iterators  */

Observe newObserve(t)
Text t; {
    if (observeHw-OBSMIN >= NUM_OBS_TAGS) {
	ERRMSG(0) "Observation storage space exhausted"
	EEND;
    }
    observe(observeHw).tag  = t;
    observe(observeHw).head = triple(OBSERVEHEAD,NIL,NIL);
    return observeHw++;
}

Observe firstObserve(){
    if (observeHw==OBSMIN) return currentObs=0;
    else 		   return currentObs=OBSMIN;
}

Observe nextObserve(){
    if (currentObs && ++currentObs < observeHw)
        return currentObs;
    else
    	return currentObs=0;
}

Void    clearObserve(){
    observeHw = OBSMIN;
}

Cell addObsInstance(s,e,id)
String s;					/* the tag                 */
Cell   e; 					/* observed expr           */
Int    id; 					/* identifying number      */
{
    Observe i;
    Triple obsCell = triple(NIL, mkInt(id), e);
    Text t         = findText(s); 

    for (i=OBSMIN; i<observeHw && t != observe(i).tag; i++)  
        ;
    if (i==observeHw) i=newObserve(t);
    appendObs(observe(i).head, obsCell);
    return obsCell;
}

Void appendObs(header, obsCell)
Cell header;
Cell obsCell; {
    if (firstObs(header) == NIL)
        firstObs(header) = obsCell;
    else
         nextObs(lastObs(header)) = obsCell;
    lastObs(header) = obsCell;
    nextObs(obsCell) = header;         		/* last cell point to header*/
}

Void insertAfterObs(old, new)
Cell old;
Cell new; {
    if (whatIs(nextObs(old)) == OBSERVEHEAD)
        lastObs(nextObs(old)) = new;		/* reset header's last ptr   */
    nextObs(new) = nextObs(old);
    nextObs(old) = new;
}

/* --------------------------------------------------------------------------
 * Breakpoint storage
 * ------------------------------------------------------------------------*/

static Breakpt breakptHw;                          /* next unused Breakpt  */
struct strBreakpt DEFTABLE(tabBreakpt,NUM_BRKPTS); /* Breakpt storage      */

Void    clearAllBreak(){
    breakptHw = BRKMIN;
}

Breakpt addBreakpt(s)		/* Add to table if absent; state= disabled */
String s; {			/* Return breakpt index			   */
    Breakpt i=BRKMIN;
    Breakpt j;
    Text t = findText(s);

    while (i<breakptHw && breakpt(i).tag<=t) i++;
    /* tag found /\ next highest found /\ end of table			   */
    if (i == breakptHw){			   /* end of table reached */
        breakpt(i).tag     = t;
	breakpt(i).enabled = FALSE;
	breakpt(i).count   = 0;
	return breakptHw++;
    }
    else if (breakpt(i).tag==t){		   /* match		   */
        return i;
    }
    else {					   /* shift and insert	   */
        for (j=breakptHw-1; j>=i; j--)
	    breakpt(j+1) = breakpt(j);
	breakpt(i).tag = t;
	breakpt(i).enabled = FALSE;
	breakptHw++;
	return i;
    }
}

Breakpt findBreakpt(s)		/* return index of breakpt name		   */
String s; {			/* return BRKMIN-1 if not found		   */
    Breakpt lower, upper, i;
    Text t = findText(s);

    lower = BRKMIN;
    upper = breakptHw-1;
    while (lower <= upper) {
        i = (lower+upper) / 2;
	if      (t < breakpt(i).tag)	upper = i - 1;
	else if (t > breakpt(i).tag)	lower = i + 1;
	else				return i;
    }
    return BRKMIN-1;
}

Bool breakNow(s)		/* break enabled && no skips 		   */
String s; {			/* decrements skip counter		   */
    Breakpt b = findBreakpt(s);
    if ((b >= BRKMIN) && breakpt(b).enabled)
        if (breakpt(b).count){ 
	    breakpt(b).count--;
	    return FALSE;
	}
	else
	    return TRUE;
    else
        return FALSE;
}


Void setBreakpt(s,v)		/* enable breakpt; may create a table entry*/
String s;
Bool v; {
    Breakpt b = findBreakpt(s);
    if (b < BRKMIN) b = addBreakpt(s);
    breakpt(b).enabled = v;
}
	
Void setBreakCount(s,n)		/* set skip count value for breakpoint	   */
String s;
Int n; {
    Breakpt b = findBreakpt(s);
    if (b >= BRKMIN) breakpt(b).count = n;
}
#endif

/* --------------------------------------------------------------------------
 * Module storage:
 *
 * A Module represents a user defined module.  
 *
 * Note: there are now two lookup mechanisms in the system:
 *
 * 1) The exports from a module are stored in a big list.
 *    We resolve qualified names, and import lists by linearly scanning
 *    through this list.
 *
 * 2) Unqualified imports and local definitions for the current module
 *    are stored in hash tables (tyconHash and nameHash) or linear lists
 *    (classes).
 *
 * ------------------------------------------------------------------------*/

static  Module    moduleHw;              /* next unused Module              */
struct  strModule DEFTABLE(tabModule,NUM_MODULE); /* Module storage         */
Module  currentModule;                  /* Module currently being processed*/

Bool isValidModule(m)                  /* is m a legitimate module id?     */
Module m; {
    return (MODMIN <= m && m < moduleHw);
}

Module newModule(t)                     /* add new module to module table  */
Text t; {
    if (moduleHw-MODMIN >= NUM_MODULE) {
	ERRMSG(0) "Module storage space exhausted"
	EEND;
    }
    module(moduleHw).text          = t; /* clear new module record         */
    module(moduleHw).tycons        = NIL;
    module(moduleHw).names         = NIL;
    module(moduleHw).classes       = NIL;
    module(moduleHw).exports       = NIL;
    module(moduleHw).modAliases    = NIL;
    module(moduleHw).modImports    = NIL;
    module(moduleHw).qualImports   = NIL;
    return moduleHw++;
}

Module findModule(t)                    /* locate Module in module table  */
Text t; {
    Module m;
    for(m=MODMIN; m<moduleHw; ++m) {
	if (module(m).text==t)
	    return m;
    }
    return NIL;
}

Module findModid(c)                    /* Find module by name or filename  */
Cell c; {
    switch (whatIs(c)) {
	case STRCELL   : { Script s = scriptThisFile(snd(c));
			   return (s==-1) ? NIL : moduleOfScript(s);
			 }
	case CONIDCELL : return findModule(textOf(c));
	default        : internal("findModid");
    }
    return NIL;/*NOTUSED*/
}

/* Don't use - use findQualifiers() instead */
Module findQualifier(t)    /* locate Module in alias list */
Text t; {
    Module ms;
    for (ms=module(currentModule).modAliases; nonNull(ms); ms=tl(ms)) {
      if ( textOf(fst(hd(ms))) == t ) {
	return snd(hd(ms));
      }
    }
    if (module(currentModule).text==t) {
      return currentModule;
    }
    return NIL;
}

/*
 * locate Modules with a local alias 't' in the import list.
 * Notice that more than one module may map to the same local
 * alias.
 */
List findQualifiers(t)   /* locate Modules in alias list */
Text t; {
    List ms;
    List res = NIL;
    
    for (ms = module(currentModule).modAliases; nonNull(ms); ms=tl(ms)) {
      if ( textOf(fst(hd(ms))) == t 
	   && !cellIsMember(snd(hd(ms)),res)) {
	  res = cons(snd(hd(ms)), res);
      }
    }
   /* Legal? "module Foo where { import Bar as Foo; ... }" */
   if (module(currentModule).text == t) {
      res = cons(currentModule,res);
   }
   return res;
}

Text findModAlias(t)  /* given a module name 't', locate its alias. */
Text t; {
    List ms;
    for (ms = module(currentModule).modAliases; nonNull(ms); ms=tl(ms)) {
	if ( module(snd(hd(ms))).text == t ) {
	    return textOf(fst(hd(ms))); 
	}
    }
    return NIL;
}	 

Void setCurrModule(m)              /* set lookup tables for current module */
Module m; {
    Int i;
    if (m!=currentModule) {
	/* The effective module import list of a module
	   is held onto until we switch to another. Ideally,
	   we'd keep around the effective import lists for
	   a module all the time (so that if a user uses
	   the :m command to evaluate/query in the context
	   of a different module, all the imported entities
	   are in scope.) However, the run-time cost of 
	   keeping these large lists around is considerable,
	   so we approximate.
	*/
	if (currentModule != NIL) {
	  module(currentModule).modImports = NIL;
	}
	currentModule = m; /* This is the only assignment to currentModule */
	for (i=0; i<TYCONHSZ; ++i)
	    tyconHash[i] = NIL;
	mapProc(hashTycon,module(m).tycons);
	for (i=0; i<NAMEHSZ; ++i)
	    nameHash[i] = NIL;
	mapProc(hashName,module(m).names);
	classes = module(m).classes;
    }
}

List getModuleImports (m) /* In 'currentModule', look up imports from 'm'. */
Module m; {
  Module ms = module(currentModule).modImports;

  for(;nonNull(ms); ms=tl(ms)) {
      if (isPair(hd(ms)) && fst(hd(ms)) == m) {
	return (snd(hd(ms)));
      }
  }
  return NIL;
}

/* --------------------------------------------------------------------------
 * Script file storage:
 *
 * script files are read into the system one after another.  The state of
 * the stored data structures (except the garbage-collected heap) is recorded
 * before reading a new script.  In the event of being unable to read the
 * script, or if otherwise requested, the system can be restored to its
 * original state immediately before the file was read.
 * ------------------------------------------------------------------------*/

typedef struct strScriptStorage {      /* record of storage state prior to */
    Text  file;                        /* reading script/module            */
    Text  textHw;
    Text  nextNewText;
    Text  nextNewDText;
    Addr  addrHw;
    Module moduleHw;
    Tycon tyconHw;
    Name  nameHw;
    Class classHw;
    Inst  instHw;
    /*
     * handle to the script's primInfoDef containing primops associated
     * with this script (if any.)
     */
    struct primInfoDef* prims;
} script;

#ifdef  DEBUG_SHOWUSE
static Void local showUse(msg,val,mx)
String msg;
Int val, mx; {
    Printf("%6s : %d of %d (%d%%)\n",msg,val,mx,(100*val)/mx);
}
#endif

static Script scriptHw;                 /* next unused script number       */
#if WANT_FIXED_SIZE_TABLES
static script scripts[NUM_SCRIPTS];     /* storage for script records      */
#else
static script* scripts = NULL;
static DynTable* dynTabScripts = NULL;  /* storage for script records      */
#endif

Script startNewScript(f)                /* start new script, keeping record */
String f; {                             /* of status for later restoration  */
#if WANT_FIXED_SIZE_TABLES
    if (scriptHw >= NUM_SCRIPTS) {
	ERRMSG(0) "Too many script files in use"
	EEND;
    }
#else
    if (scriptHw >= (Int)(dynTabScripts->maxIdx)) {
      growDynTable(dynTabScripts);
      scripts = (script*)(dynTabScripts->data);
    }
#endif
#if DEBUG_SHOWUSE
    showUse("Text",   textHw,           NUM_TEXT);
    showUse("Addr",   addrHw,           NUM_ADDRS);
    showUse("Module", moduleHw-MODMIN,  NUM_MODULE);
    showUse("Tycon",  tyconHw-TYCMIN,   NUM_TYCON);
    showUse("Name",   nameHw-NAMEMIN,   NUM_NAME);
#if WANT_FIXED_SIZE_TABLES
    showUse("Class",  classHw-CLASSMIN, NUM_CLASSES);
    showUse("Inst",   instHw-INSTMIN,   NUM_INSTS);
#else
    showUse("Class",  classHw-CLASSMIN, dynTabClass->maxIdx);
    showUse("Inst",   instHw-INSTMIN,   dynTabInst->maxIdx);
#endif
#endif

    scripts[scriptHw].file         = findText( f ? f : "<nofile>" );
    scripts[scriptHw].textHw       = textHw;
    scripts[scriptHw].nextNewText  = nextNewText;
    scripts[scriptHw].nextNewDText = nextNewDText;
    scripts[scriptHw].addrHw       = addrHw;
    scripts[scriptHw].moduleHw     = moduleHw;
    scripts[scriptHw].tyconHw      = tyconHw;
    scripts[scriptHw].nameHw       = nameHw;
    scripts[scriptHw].classHw      = classHw;
    scripts[scriptHw].instHw       = instHw;
    scripts[scriptHw].prims        = NULL;

    return scriptHw++;
}

Bool isPreludeScript() {                /* Test whether this is the Prelude*/
    return (scriptHw==0);
}

Bool moduleThisScript(m)                /* Test if given module is defined */
Module m; {                             /* in current script file          */
    return scriptHw<1 || m>=scripts[scriptHw-1].moduleHw;
}

Module lastModule() {              /* Return module in current script file */
    return (moduleHw>MODMIN ? moduleHw-1 : modulePrelude);
}

#define scriptThis(nm,t,tag) \
        Script nm(x)                   \
  	t x; {                         \
	  Script s=0;                  \
	  while (s<scriptHw            \
	       && x>=scripts[s].tag)   \
  	    s++;                       \
          return s;                    \
	}

scriptThis(scriptThisName,Name,nameHw)
scriptThis(scriptThisTycon,Tycon,tyconHw)
scriptThis(scriptThisInst,Inst,instHw)
scriptThis(scriptThisClass,Class,classHw)
#undef scriptThis

Module moduleOfScript(s)
Script s; {
    return (s==0) ? modulePrelude : scripts[s-1].moduleHw;
}

String fileOfModule(m)
Module m; {
    Script s;
    if (m == modulePrelude) {
	return findMPathname(STD_PRELUDE_HUGS);
    }
    for(s=0; s<scriptHw; ++s) {
	if ( scripts[s].moduleHw == m ) {
	    return textToStr(scripts[s].file);
	}
    }
    return 0;
}

Script scriptThisFile(f)
Text f; {
    Script s;
    for (s=0; s < scriptHw; ++s) {
	if (scripts[s].file == f) {
	    return s+1;
	}
    }
    if (f == textPrelude) {
	return 0;
    }
    return (-1);
}

Void dropAScript(sno)   /* elide one script from the stack */
Script sno; {

    int i = sno + 1;
    
    while (i < scriptHw) {
	scripts[i-1].file = scripts[i].file;
	scripts[i-1].textHw = scripts[i].textHw;
	scripts[i-1].nextNewText = scripts[i].nextNewText;
	scripts[i-1].nextNewDText = scripts[i].nextNewDText;
	scripts[i-1].addrHw = scripts[i].addrHw;
	scripts[i-1].moduleHw = scripts[i].moduleHw;
	scripts[i-1].tyconHw = scripts[i].tyconHw;
	scripts[i-1].nameHw = scripts[i].nameHw;
	scripts[i-1].classHw = scripts[i].classHw;
	scripts[i-1].instHw = scripts[i].instHw;
	if (scripts[i-1].prims) {
	  freePrimInfo(scripts[i-1].prims);
	  scripts[i-1].prims = 0;
	}
	scripts[i-1].prims = scripts[i].prims;

	i++;
    }
}

Void dropScriptsFrom(sno)               /* Restore storage to state prior  */
Script sno; {                           /* to reading script sno           */
    if (sno >= 0 && sno < scriptHw) {   /* is there anything to restore?   */
	int i;
	textHw       = scripts[sno].textHw;
	nextNewText  = scripts[sno].nextNewText;
	nextNewDText = scripts[sno].nextNewDText;
	moduleHw     = scripts[sno].moduleHw;
	addrHw       = scripts[sno].addrHw;
	tyconHw      = scripts[sno].tyconHw;
	nameHw       = scripts[sno].nameHw;
	classHw      = scripts[sno].classHw;
	instHw       = scripts[sno].instHw;

	for (i=0; i<TEXTHSZ; ++i) {
	    int j = 0;
	    while (j<NUM_TEXTH && textHash[i][j]!=NOTEXT
			       && textHash[i][j]<textHw)
		++j;
	    if (j<NUM_TEXTH)
		textHash[i][j] = NOTEXT;
	}

	currentModule=NIL;
	for (i=0; i<TYCONHSZ; ++i) {
	    tyconHash[i] = NIL;
	}
	for (i=0; i<NAMEHSZ; ++i) {
	    nameHash[i] = NIL;
	}

	for (i=CLASSMIN; i<classHw; i++) {
	    List ins = cclass(i).instances;
	    List is  = NIL;

	    while (nonNull(ins)) {
		List temp = tl(ins);
		if (hd(ins)<instHw) {
		    tl(ins) = is;
		    is      = ins;
		}
		ins = temp;
	    }
	    cclass(i).instances = rev(is);
	}

	i = sno;
	while (i < scriptHw) {
	  if (scripts[i].prims) {
	    freePrimInfo(scripts[i].prims);
            scripts[i].prims = 0;
	  }
	  i++;
	}
	scriptHw = sno;
    }
}

Void setScriptPrims(p)  /* set the current script's primitive record. */
void* p; {
  scripts[scriptHw-1].prims = (struct primInfoDef*)p;
  return;
}

/* --------------------------------------------------------------------------
 * Heap storage:
 *
 * Provides a garbage collectable heap for storage of expressions etc.
 * ------------------------------------------------------------------------*/

Int     heapSize = DEFAULTHEAP;         /* number of cells in heap         */
Heap    heapFst;                        /* array of fst component of pairs */
Heap    heapSnd;                        /* array of snd component of pairs */
#ifndef GLOBALfst
Heap    heapTopFst;
#endif
#ifndef GLOBALsnd
Heap    heapTopSnd;
#endif
Bool    consGC = TRUE;                  /* Set to FALSE to turn off gc from*/
					/* C stack; use with extreme care! */
#if     PROFILING
Heap    heapThd, heapTopThd;            /* to keep record of producers     */
Int     sysCount;                       /* record unattached cells         */
Name    producer;                       /* current producer, if any        */
Bool    profiling = FALSE;              /* should profiling be performed   */
Int     profInterval = MAXPOSINT;       /* interval between samples        */
FILE    *profile = 0;                   /* pointer to profiler log, if any */
#endif
Long    numCells;
Int     numGcs;				/* number of garbage collections   */
Int     cellsRecovered;                 /* number of cells recovered       */

static  Cell freeList;                  /* free list of unused cells       */
static  Cell lsave, rsave;              /* save components of pair         */

#if GC_WEAKPTRS
static List weakPtrs;			/* list of weak ptrs		   */
					/* reconstructed during every GC   */
List   finalizers = NIL;
List   liveWeakPtrs = NIL;
#endif

#if GC_STATISTICS

static Int markCount, stackRoots;

#define initStackRoots() stackRoots = 0
#define recordStackRoot() stackRoots++

#define startGC()       \
    if (gcMessages) {   \
	Printf("\n");   \
	fflush(stdout); \
    }
#define endGC()         \
    if (gcMessages) {   \
	Printf("\n");   \
	fflush(stdout); \
    }

#define start()      markCount = 0
#define end(thing,rs) \
    if (gcMessages) { \
	Printf("GC: %-18s: %4d cells, %4d roots.\n", thing, markCount, rs); \
	fflush(stdout); \
    }
#define recordMark() markCount++

#else /* !GC_STATISTICS */

#define startGC()
#define endGC()

#define initStackRoots()
#define recordStackRoot()

#define start()   
#define end(thing,root) 
#define recordMark() 

#endif /* !GC_STATISTICS */

Cell pair(l,r)                          /* Allocate pair (l, r) from       */
Cell l, r; {                            /* heap, garbage collecting first  */
    Cell c = freeList;                  /* if necessary ...                */

    if (isNull(c)) {
	lsave = l;
	rsave = r;
	garbageCollect();
	l     = lsave;
	lsave = NIL;
	r     = rsave;
	rsave = NIL;
	c     = freeList;
    }
    freeList = snd(freeList);
    fst(c)   = l;
    snd(c)   = r;
#if PROFILING
    thd(c)   = producer;
#endif
    numCells++;
    return c;
}

Void overwrite(dst,src)                 /* overwrite dst cell with src cell*/
Cell dst, src; {                        /* both *MUST* be pairs            */
    if (isPair(dst) && isPair(src)) {
	fst(dst) = fst(src);
	snd(dst) = snd(src);
    }
    else
	internal("overwrite");
}

static Int *marks;
static Int marksSize;

Cell markExpr(c)                        /* External interface to markCell  */
Cell c; {
    return isGenPair(c) ? markCell(c) : c;
}

static Cell local markCell(c)           /* Traverse part of graph marking  */
Cell c; {                               /* cells reachable from given root */
					/* markCell(c) is only called if c */
					/* is a pair                       */
mc: switch (fst(c)) {
	case INDIRECT : c = indirectChain(c);
			if (isGenPair(c))
			    goto mc;
			return c;
#if GC_WEAKPTRS
	case WEAKCELL :
			{
			  register int place = placeInSet(c);
			  register int mask  = maskInSet(c);
			  if (!(marks[place]&mask)) {
			    marks[place] |= mask;
			    marks[placeInSet(snd(c))] |= maskInSet(snd(c));
			    /* printf("Found Weak Pointer %d\n", c); */
			    nextWeakPtr(c) = weakPtrs;
			    weakPtrs = c;
			    recordMark();
			  }
			  return c;
			}
#endif
    }

    {   register int place = placeInSet(c);
	register int mask  = maskInSet(c);
	if (marks[place]&mask)
	    return c;
	else {
	    marks[place] |= mask;
	    recordMark();
	}
    }

    /* STACK_CHECK: Avoid stack overflows during recursive marking. */
    if (isGenPair(fst(c))) {
	STACK_CHECK
	fst(c) = markCell(fst(c));
	return markSnd(c);
    }
    else if (isNull(fst(c)) || fst(c)>=BCSTAG) {
	STACK_CHECK
	return markSnd(c);
    } else {
        return c;
    }
}

static Cell local markSnd(c)            /* Variant of markCell used to     */
Cell c; {                               /* update snd component of cell    */
    Cell t;                             /* using tail recursion            */
    Cell orig;
    
    orig = c;

ma: t = c;                              /* Keep pointer to original pair   */
    c = snd(c);
mb: if (!isPair(c))
	return orig;

    switch (fst(c)) {
	case INDIRECT : snd(t) = c = indirectChain(c);
			goto mb;
#if GC_WEAKPTRS
	case WEAKCELL :
			{
			  register int place = placeInSet(c);
			  register int mask  = maskInSet(c);
			  if (!(marks[place]&mask)) {
			    marks[place] |= mask;
			    marks[placeInSet(snd(c))] |= maskInSet(snd(c));
			    nextWeakPtr(c) = weakPtrs;
			    weakPtrs = c;
			    recordMark();
			  }
			  return orig;
			}
#endif
    }

    {   register int place = placeInSet(c);
	register int mask  = maskInSet(c);
	if (marks[place]&mask)
	    return orig;
	else {
	    marks[place] |= mask;
	    recordMark();
	}
    }

    if (isGenPair(fst(c))) {
	fst(c) = markCell(fst(c));
	goto ma;
    }
    else if (isNull(fst(c)) || fst(c)>=BCSTAG)
	goto ma;
    return orig;
}

static Cell local indirectChain(c)      /* Scan chain of indirections      */
Cell c; {                               /* Detecting loops of indirections */
    Cell is = c;                        /* Uses pointer reversal ...       */
    c       = snd(is);
    snd(is) = NIL;
    fst(is) = INDIRECT1;

    while (isPair(c) && fst(c)==INDIRECT) {
	register Cell temp = snd(c);
	snd(c)  = is;
	is      = c;
	c       = temp;
	fst(is) = INDIRECT1;
    }

    if (isPair(c) && fst(c)==INDIRECT1)
	c = nameBlackHole;

    do {
	register Cell temp = snd(is);
	fst(is) = INDIRECT;
	snd(is) = c;
	is      = temp;
    } while (nonNull(is));

    return c;
}

Void markWithoutMove(n)                 /* Garbage collect cell at n, as if*/
Cell n; {                               /* it was a cell ref, but don't    */
					/* move cell (i.e. retain INDIRECT */
					/* at top level) so we don't have  */
					/* to modify the stored value of n */
    if (isGenPair(n)) {
	recordStackRoot();
	if (fst(n)==INDIRECT) {         /* special case for indirections   */
	    register int place = placeInSet(n);
	    register int mask  = maskInSet(n);
	    marks[place]  |= mask;
	    recordMark();
	    markSnd(n);
	}
	else
	    markCell(n);                /* normal pairs don't move anyway  */
    }
}

static Bool local isMarked(c)
Cell c; {
    if (isGenPair(c)) {
	Int place = placeInSet(c);
	Int mask  = maskInSet(c);
	return (marks[place]&mask)!=0;
    } else {
	return TRUE;
    }
}

Void garbageCollect()     {             /* Run garbage collector ...       */
    Bool breakStat = breakOn(FALSE);    /* disable break checking          */
    Int i,j;
    register Int mask;
    register Int place;
    Int      recovered;
    jmp_buf  regs;                      /* save registers on stack         */
    setjmp(regs);

    gcStarted();
    for (i=0; i<marksSize; ++i)         /* initialise mark set to empty    */
	marks[i] = 0;
#if GC_WEAKPTRS
    weakPtrs = NIL;                     /* clear list of weak pointers     */
#endif
    everybody(MARK);                    /* Mark all components of system   */

#if IO_HANDLES
#if WANT_FIXED_SIZE_TABLES
    for (i=0; i<(Int)NUM_HANDLES; ++i)  /* release any unused handles      */
#else
    for (i=0; i<(Int)num_handles; ++i)  /* release any unused handles      */
#endif
	if (nonNull(handles[i].hcell)) {
	    register int place = placeInSet(handles[i].hcell);
	    register int mask  = maskInSet(handles[i].hcell);
	    if ((marks[place]&mask)==0)
		freeHandle(i);
	}
#endif
#if GC_MALLOCPTRS
    for (i=mallocPtr_hw-1; i >= 0; i--) { /* release any unused mallocptrs   */
	if (isPair(mallocPtrs[i].mpcell)) {
	    register int place = placeInSet(mallocPtrs[i].mpcell);
	    register int mask  = maskInSet(mallocPtrs[i].mpcell);
	    if ((marks[place]&mask)==0)
		incMallocPtrRefCnt(i,-1);
	}
    }
#endif /* GC_MALLOCPTRS */

#if GC_WEAKPTRS
    /* After GC completes, we scan the list of weak pointers that are
     * still live and zap their contents unless the contents are still
     * live (by some other means).
     * Note that this means the contents must itself be heap allocated.
     * This means it can't be a nullary constructor or an Int or a Name
     * or lots of other things - hope this doesn't bite too hard.
     */
    for (; nonNull(weakPtrs); weakPtrs=nextWeakPtr(weakPtrs)) {
	Cell ptr = derefWeakPtr(weakPtrs);
	if (isGenPair(ptr)) {
	    Int  place = placeInSet(ptr);
	    Int  mask  = maskInSet(ptr);
	    if ((marks[place]&mask)==0) {
		/* printf("Zapping weak pointer %d\n", ptr); */
		derefWeakPtr(weakPtrs) = NIL;
	    } else {
		/* printf("Keeping weak pointer %d\n", ptr); */
	    }
	} else if (nonNull(ptr)) {
	    printf("Weak ptr contains object which isn't heap allocated %d\n", ptr);
	}
    }

    if (nonNull(liveWeakPtrs) || nonNull(finalizers)) {
	Bool anyMarked;			/* Weak pointers with finalizers   */
	List wps;
	List newFins = NIL;

	/* Step 1: iterate until we've found out what is reachable	   */
	do {
	    anyMarked = FALSE;
	    for (wps=liveWeakPtrs; nonNull(wps); wps=tl(wps)) {
		Cell wp = hd(wps);
		Cell k  = fst(snd(wp));
		if (isNull(k)) {
		    internal("bad weak ptr");
		}
		if (isMarked(k)) {
		    Cell vf = snd(snd(wp));
		    if (!isMarked(fst(vf)) || !isMarked(snd(vf))) {
			mark(fst(vf));
			mark(snd(vf));
			anyMarked = TRUE;
		    }
		}
	    }
	} while (anyMarked);

	/* Step 2: Now we know which weak pointers will die, so we can	   */
	/* remove them from the live set and gather their finalizers.  But */
	/* note that we mustn't mark *anything* at this stage or we will   */
	/* corrupt our view of what's alive, and what's dead.		   */
	wps = NIL;
	while (nonNull(liveWeakPtrs)) {
	    Cell wp = hd(liveWeakPtrs);
	    List nx = tl(liveWeakPtrs);
	    Cell k  = fst(snd(wp));
	    if (!isMarked(k)) {			/* If the key is dead, then*/
		Cell vf      = snd(snd(wp));	/* stomp on weak pointer   */
		if (nonNull(snd(vf))) {
		    fst(vf)  = snd(vf);
		    snd(vf)  = newFins;
		    newFins  = vf;		/* reuse because we can't  */
		}				/* reallocate here ...	   */
		fst(snd(wp)) = NIL;
		snd(snd(wp)) = NIL;
		snd(wp)      = NIL;
		liveWeakPtrs = nx;
	    } else {
		tl(liveWeakPtrs) = wps;		/* Otherwise, weak pointer */
		wps              = liveWeakPtrs;/* survives to face another*/
		liveWeakPtrs     = nx;		/* garbage collection	   */
	    }
	}
	liveWeakPtrs = wps;

	/* Step 3: Now we've identified the live cells and the newly	   */
	/* scheduled finalizers, but we had better make sure that they are */
	/* all marked now, including any internal structure, to ensure that*/
	/* they make it to the other side of gc.			   */
	for (; nonNull(wps); wps=tl(wps)) {
	    mark(snd(hd(wps)));
	}
	mark(liveWeakPtrs);
        mark(newFins);
	finalizers = revOnto(newFins,finalizers);
    }

#endif /* GC_WEAKPTRS */
    gcScanning();                       /* scan mark set                   */
    mask      = 1;
    place     = 0;
    recovered = 0;
    j         = 0;
#if PROFILING
    if (profile) {
	sysCount = 0;
	for (i=NAMEMIN; i<nameHw; i++)
	    name(i).count = 0;
    }
#endif
    freeList = NIL;
    for (i=1; i<=heapSize; i++) {
	if ((marks[place] & mask) == 0) {
	    snd(-i)  = freeList;
	    fst(-i)  = FREECELL;
	    freeList = -i;
	    recovered++;
	}
#if PROFILING
	else if (nonNull(thd(-i)))
	    name(thd(-i)).count++;
	else
	    sysCount++;
#endif
	mask <<= 1;
	if (++j == bitsPerWord) {
	    place++;
	    mask = 1;
	    j    = 0;
	}
    }

    gcRecovered(recovered);
    breakOn(breakStat);                 /* restore break trapping if nec.  */

#if PROFILING
    if (profile) {
	fprintf(profile,"BEGIN_SAMPLE %ld.00\n",numReductions);
/* For the time being, we won't include the system count in the output:
	if (sysCount>0)
	    fprintf(profile,"  SYSTEM %d\n",sysCount);
*/
	/* Accumulate costs in top level objects */
	for (i=NAMEMIN; i<nameHw; i++) {
	    Name cc = i;
	    /* Use of "while" instead of "if" is pure paranoia - ADR */
	    while (isName(name(cc).parent)) 
		cc = name(cc).parent;
	    if (i != cc) {
		name(cc).count += name(i).count;
		name(i).count = 0;
	    }
	}
	for (i=NAMEMIN; i<nameHw; i++)
	    if (name(i).count>0) 
		if (isPair(name(i).parent)) {
		    Pair p = name(i).parent;
		    Cell f = fst(p);
		    fprintf(profile,"  ");
		    if (isClass(f))
			fprintf(profile,"%s",textToStr(cclass(f).text));
		    else {
			fprintf(profile,"%s_",textToStr(cclass(inst(f).c).text));
			/* Will hp2ps accept the spaces produced by this? */
			printPred(profile,inst(f).head);
		    }
		    fprintf(profile,"_%s %d\n",
			    textToStr(name(snd(p)).text),
			    name(i).count);
		} else {
		    fprintf(profile,"  %s %d\n",
			    textToStr(name(i).text),
			    name(i).count);
		}
	fprintf(profile,"END_SAMPLE %ld.00\n",numReductions);
    }
#endif

    /* can only return if freeList is nonempty on return. */
    if (recovered<minRecovery || isNull(freeList)) {
	ERRMSG(0) "Garbage collection fails to reclaim sufficient space"
	EEND;
    }
    numGcs++;
    cellsRecovered = recovered;
}

#if PROFILING
Void profilerLog(s)                     /* turn heap profiling on, saving log*/
String s; {                             /* in specified file                 */
    if ((profile=fopen(s,"w")) != NULL) {
	fprintf(profile,"JOB \"Hugs Heap Profile\"\n");
	fprintf(profile,"DATE \"%s\"\n",timeString());
	fprintf(profile,"SAMPLE_UNIT \"reductions\"\n");
	fprintf(profile,"VALUE_UNIT \"cells\"\n");
    }
    else {
	ERRMSG(0) "Cannot open profile log file \"%s\"", s
	EEND;
    }
}
#endif

/* --------------------------------------------------------------------------
 * Code for saving last expression entered:
 *
 * This is a little tricky because some text values (e.g. strings or variable
 * names) may not be defined or have the same value when the expression is
 * recalled.  These text values are therefore saved in the top portion of
 * the text table.
 * ------------------------------------------------------------------------*/

static Cell lastExprSaved;              /* last expression to be saved     */

Void setLastExpr(e)                     /* save expression for later recall*/
Cell e; {
    lastExprSaved = NIL;                /* in case attempt to save fails   */
    savedText     = NUM_TEXT;
    lastExprSaved = lowLevelLastIn(e);
}

static Cell local lowLevelLastIn(c)     /* Duplicate expression tree (i.e. */
Cell c; {                               /* acyclic graph) for later recall */
    if (isPair(c))                      /* Duplicating any text strings    */
	if (isBoxTag(fst(c)))           /* in case these are lost at some  */
	    switch (fst(c)) {           /* point before the expr is reused */
		case VARIDCELL :
		case VAROPCELL :
		case DICTVAR   :
		case CONIDCELL :
		case CONOPCELL :
		case STRCELL   : return pair(fst(c),saveText(textOf(c)));
		default        : return pair(fst(c),snd(c));
	    }
	else
	    return pair(lowLevelLastIn(fst(c)),lowLevelLastIn(snd(c)));
    else
	return c;
}

Cell getLastExpr() {                    /* recover previously saved expr   */
    return lowLevelLastOut(lastExprSaved);
}

static Cell local lowLevelLastOut(c)    /* As with lowLevelLastIn() above  */
Cell c; {                               /* except that Cells refering to   */
    if (isPair(c))                      /* Text values are restored to     */
	if (isBoxTag(fst(c)))           /* appropriate values              */
	    switch (fst(c)) {
		case VARIDCELL :
		case VAROPCELL :
		case DICTVAR   :
		case CONIDCELL :
		case CONOPCELL :
		case STRCELL   : return pair(fst(c),
					     findText(text+intValOf(c)));
		default        : return pair(fst(c),snd(c));
	    }
	else
	    return pair(lowLevelLastOut(fst(c)),lowLevelLastOut(snd(c)));
    else
	return c;
}

/* --------------------------------------------------------------------------
 * Miscellaneous operations on heap cells:
 * ------------------------------------------------------------------------*/

/* Profiling suggests that the number of calls to whatIs() is typically    */
/* rather high.  The recoded version below attempts to improve the average */
/* performance for whatIs() using a binary search for part of the analysis */

Cell whatIs(c)                         /* identify type of cell            */
register Cell c; {
    if (isPair(c)) {
	register Cell fstc = fst(c);
	return isTag(fstc) ? fstc : AP;
    }
    if (c<TUPMIN)    return c;
    if (c>=INTMIN)   return INTCELL;

    if (c>=NAMEMIN) if (c>=CLASSMIN)    if (c>=CHARMIN) return CHARCELL;
					else            return CLASS;
		    else                if (c>=INSTMIN) return INSTANCE;
					else            return NAME;
    else            if (c>=MODMIN)      if (c>=TYCMIN)  return TYCON;
					else            return MODULE;
		    else		if (c>=OFFMIN)  return OFFSET;
					else		return TUPLE;

/*  if (isPair(c)) {
	register Cell fstc = fst(c);
	return isTag(fstc) ? fstc : AP;
    }
    if (c>=INTMIN)   return INTCELL;
    if (c>=CHARMIN)  return CHARCELL;
    if (c>=CLASSMIN) return CLASS;
    if (c>=INSTMIN)  return INSTANCE;
    if (c>=NAMEMIN)  return NAME;
    if (c>=TYCMIN)   return TYCON;
    if (c>=MODMIN)   return MODULE;
    if (c>=OFFMIN)   return OFFSET;
    if (c>=TUPMIN)   return TUPLE;
    return c;*/
}

#if DEBUG_PRINTER
/* A very, very simple printer.
 * Output is uglier than from printExp - but the printer is more
 * robust and can be used on any data structure irrespective of
 * its type.
 */
Void printList Args((List, Int));
Void print Args((Cell, Int));
Void print(c, depth)
Cell c;
Int  depth; {
    if (0 == depth) {
	Printf("...");
#if 0 /* Not in this version of Hugs */
    } else if (isPair(c) && !isGenPair(c)) {
	extern Void printEvalCell Args((Cell, Int));
	printEvalCell(c,depth);
#endif
    } else {
	Int tag = whatIs(c);
	switch (tag) {
	  case AP : 
	      Putchar('(');
	      print(fst(c), depth-1);
	      Putchar(',');
	      print(snd(c), depth-1);
	      Putchar(')');
	      break;
	  case FREECELL :
	      Printf("free(%d)", c);
	      break;
	  case INTCELL :
	      Printf("int(%d)", intOf(c));
	      break;
	  case FLOATCELL :
	      Printf("float(%f)", floatOf(c));
	      break;
	  case DOUBLECELL :
	      Printf("double(%f)", doubleOf(c));
	      break;
	  case CHARCELL :
	      Printf("char('%c')", charOf(c));
	      break;
	  case CLASS :
	      Printf("class(%d)", c-CLASSMIN);
	      if (CLASSMIN <= c && c < classHw)
		  Printf("=\"%s\"", textToStr(cclass(c).text));
	      break;
	  case INSTANCE :
	      Printf("instance(%d)", c - INSTMIN);
	      break;
	  case NAME :
	      Printf("name(%d)", c-NAMEMIN);
	      if (NAMEMIN <= c && c < nameHw)
		  Printf("=\"%s\"", textToStr(name(c).text));
	      break;
	  case TYCON :
	      Printf("tycon(%d)", c-TYCMIN);
	      if (TYCMIN <= c && c < tyconHw)
		  Printf("=\"%s\"", textToStr(tycon(c).text));
	      break;
	  case MODULE :
	      Printf("module(%d)", c - MODMIN);
	      break;
	  case OFFSET :
	      Printf("Offset %d", offsetOf(c));
	      break;
	  case TUPLE :
	      Printf("Tuple %d", tupleOf(c));
	      break;
	  case NIL :
	      Printf("NIL");
	      break;
	  case DOTDOT :
	      Printf("DOTDOT");
	      break;
	  case DICTVAR :
	      Printf("{dict %d}",textOf(c));
	      break;
	  case VARIDCELL :
	  case VAROPCELL :
	  case CONIDCELL :
	  case CONOPCELL :
	      Printf("{id %s}",textToStr(textOf(c)));
	      break;
#if IPARAM
	  case IPCELL :
	      Printf("{ip %s}",textToStr(textOf(c)));
	      break;
	  case IPVAR :
	      Printf("?%s",textToStr(textOf(c)));
	      break;
#endif
	  case QUALIDENT :
	      Printf("{qid %s.%s}",textToStr(qmodOf(c)),textToStr(qtextOf(c)));
	      break;
	  case LETREC:
	      Printf("LetRec(");
	      print(fst(snd(c)),depth-1);
	      Putchar(',');
	      print(snd(snd(c)),depth-1);
	      Putchar(')');
	      break;
#if OBSERVATIONS
          case INDIRECT:
              Printf("->");
              print(snd(c),depth);
              break;
          case OBSERVE:
              Printf("{==>"); print(snd3(c),depth); Putchar('|');
              Printf("cell = %d=(", thd3(c));
              Printf("next= %d,", nextObs(thd3(c)));
              Printf("seq= %d,", intOf(seqObs(thd3(c))));
              Printf("expr= %d)}", exprObs(thd3(c)));
              break;
          case OBSERVESTK:
              Printf("{=STK=>{");
              Printf("cell = %d=(", thd3(c));
              Printf("next= %d,", nextObs(thd3(c)));
              Printf("seq= %d,", intOf(seqObs(thd3(c))));
              Printf("expr= %d)}", exprObs(thd3(c)));
              break;
#endif
	  case BIGLAM:
	      Printf("BigLam(");
	      printList(fst(snd(c)),depth-1);
	      Putchar(',');
	      print(snd(snd(c)),depth-1);
	      Putchar(')');
	      break;
	  case ESIGN:
	      Printf("ESign(");
	      print(fst(snd(c)),depth-1);
	      Putchar(',');
	      print(snd(snd(c)),depth-1);
	      Putchar(')');
	      break;
	  case COMP:
	      Printf("COMP(");
	      print(fst(snd(c)),depth-1);
	      Putchar(',');
	      print(snd(snd(c)),depth-1);
	      Putchar(')');
	      break;
	  case FROMQUAL:
	      Printf("FROMQUAL(");
	      print(fst(snd(c)),depth-1);
	      Putchar(',');
	      print(snd(snd(c)),depth-1);
	      Putchar(')');
	      break;
	  default :
	      if (isBoxTag(tag)) {
		  Printf("Tag(%d)=%d", c, tag);
	      } else if (isConTag(tag)) {
		  Printf("%d@(%d,",c,tag);
		  print(snd(c), depth-1);
		  Putchar(')');
		  break;
	      } else if (c == tag) {
		  Printf("Tag(%d)", c);
	      } else {
		  Printf("Tag(%d)=%d", c, tag);
	      }
	      break;
	}
    }
    FlushStdout();
}

Void printList(l, depth)
List l;
Int  depth; {
    Int tag;
    Cell n;
    Putchar('[');
    if ((tag = whatIs(l)) != NIL)
	for (; ; l=n) {
	    if (tag == AP) {
		print(fst(l), depth-1);
		n = snd(l);
		tag = whatIs(n);
		if (tag == NIL)
		    break;
		Putchar(',');
	    } else {
		Printf("NotAList!\n");
		break;
	    }
	}
    Putchar(']');
}
#endif

Bool isVar(c)                           /* is cell a VARIDCELL/VAROPCELL ? */
Cell c; {                               /* also recognises DICTVAR cells   */
    return isPair(c) &&
	       (fst(c)==VARIDCELL || fst(c)==VAROPCELL || fst(c)==DICTVAR);
}

Bool isCon(c)                          /* is cell a CONIDCELL/CONOPCELL ?  */
Cell c; {
    return isPair(c) && (fst(c)==CONIDCELL || fst(c)==CONOPCELL);
}

Bool isQVar(c)			      /* is cell a [un]qualified varop/id? */
Cell c; {
    if (!isPair(c)) return FALSE;
    switch (fst(c)) {
	case VARIDCELL  :
	case VAROPCELL  : return TRUE;

	case QUALIDENT  : return isVar(snd(snd(c)));

	default         : return FALSE;
    }
}

Bool isQCon(c)			       /*is cell a [un]qualified conop/id? */
Cell c; {
    if (!isPair(c)) return FALSE;
    switch (fst(c)) {
	case CONIDCELL  :
	case CONOPCELL  : return TRUE;

	case QUALIDENT  : return isCon(snd(snd(c)));

	default         : return FALSE;
    }
}

Bool isQualIdent(c)                    /* is cell a qualified identifier?  */
Cell c; {
    return isPair(c) && (fst(c)==QUALIDENT);
}

Bool isIdent(c)			       /* is cell an identifier?           */
Cell c; {
    if (!isPair(c)) return FALSE;
    switch (fst(c)) {
	case VARIDCELL  :
	case VAROPCELL  :
	case CONIDCELL  :
	case CONOPCELL  : return TRUE;

	case QUALIDENT  : return TRUE;

	default         : return FALSE;
    }
}

Bool isInt(c)                          /* cell holds integer value?        */
Cell c; {
    return isSmall(c) || (isPair(c) && fst(c)==INTCELL);
}

Int intOf(c)                           /* find integer value of cell?      */
Cell c; {
    return isPair(c) ? (Int)(snd(c)) : (Int)(c-INTZERO);
}

Cell mkInt(n)                          /* make cell representing integer   */
Int n; {
    return (MINSMALLINT <= n && n <= MAXSMALLINT)
	   ? INTZERO+n
	   : pair(INTCELL,n);
}

#if BIGNUMS
Bool isBignum(c)                       /* cell holds bignum value?         */
Cell c; {
    return c==ZERONUM || (isPair(c) && (fst(c)==POSNUM || fst(c)==NEGNUM));
}
#endif

#if SIZEOF_INTP == SIZEOF_INT
typedef union {Int i; Pointer p;} IntOrPointer;
Cell mkPtr(p)
Pointer p;
{
    IntOrPointer x;
    x.p = p;
    return pair(PTRCELL,x.i);
}

Pointer ptrOf(c)
Cell c;
{
    IntOrPointer x;
    assert(fst(c) == PTRCELL);
    x.i = snd(c);
    return x.p;
}
#elif SIZEOF_INTP == 2*SIZEOF_INT
typedef union {struct {Int i1; Int i2;} i; Pointer p;} IntOrPointer;
Cell mkPtr(p)
Pointer p;
{
    IntOrPointer x;
    x.p = p;
    return pair(PTRCELL,pair(mkInt(x.i.i1),mkInt(x.i.i2)));
}

Pointer ptrOf(c)
Cell c;
{
    IntOrPointer x;
    assert(fst(c) == PTRCELL);
    x.i.i1 = intOf(fst(snd(c)));
    x.i.i2 = intOf(snd(snd(c)));
    return x.p;
}
#else
/* warning "type Ptr not supported on this architecture - don't use it" */
Cell mkPtr(p)
Pointer p;
{
    ERRMSG(0) "mkPtr: type Ptr not supported on this architecture"
    EEND;
}

Pointer ptrOf(c)
Cell c;
{
    ERRMSG(0) "ptrOf: type Ptr not supported on this architecture"
    EEND;
}
#endif

/* --------------------------------------------------------------------------
 * List operations:
 * ------------------------------------------------------------------------*/

Int length(xs)                         /* calculate length of list xs      */
List xs; {
    Int n = 0;
    for (; nonNull(xs); ++n)
	xs = tl(xs);
    return n;
}

List appendOnto(xs,ys)                 /* Destructively prepend xs onto    */
List xs, ys; {                         /* ys by modifying xs ...           */
    if (isNull(xs))
	return ys;
    else {
	List zs = xs;
	while (nonNull(tl(zs)))
	    zs = tl(zs);
	tl(zs) = ys;
	return xs;
    }
}

List dupOnto(xs,ys)      /* non-destructively prepend xs backwards onto ys */
List xs; 
List ys; {
    for (; nonNull(xs); xs=tl(xs))
	ys = cons(hd(xs),ys);
    return ys;
}

List dupList(xs)                       /* Duplicate spine of list xs       */
List xs; {
    List ys = NIL;
    for (; nonNull(xs); xs=tl(xs))
	ys = cons(hd(xs),ys);
    return rev(ys);
}

List dupUpto(xs,c)                     /* Duplicate spine of list xs       */
List xs;
Cell c; {
    List ys = NIL;
    for (; nonNull(xs) && hd(xs) != c; xs=tl(xs))
	ys = cons(hd(xs),ys);
    return rev(ys);
}

List revOnto(xs,ys)                    /* Destructively reverse elements of*/
List xs, ys; {                         /* list xs onto list ys...          */
    Cell zs;

    while (nonNull(xs)) {
	zs     = tl(xs);
	tl(xs) = ys;
	ys     = xs;
	xs     = zs;
    }
    return ys;
}

#if 0
List delete(xs,y)                      /* Delete first use of y from xs    */
List xs;
Cell y; {
    if (isNull(xs)) {
	return xs;
    } else if (hs(xs) == y) {
	return tl(xs);
    } else {
	tl(xs) = delete(tl(xs),y);
	return xs;
    }
}

List minus(xs,ys)                      /* Delete members of ys from xs     */
List xs, ys; {
    mapAccum(delete,xs,ys);
    return xs;
}
#endif

List concat(xss)
List xss; {
    List xs = NIL;
    for (; nonNull(xss); xss=tl(xss))
	xs = dupOnto(hd(xss),xs);
    return xs;
}

List intersect(xs,ys)
List xs, ys; {
    List zs = NIL;
    for (;nonNull(xs);xs=tl(xs)) {
	if (varIsMember(textOf(hd(xs)),ys))
	    zs = cons(hd(xs),zs);
    }
    return zs;
}

Cell varIsMember(t,xs)                 /* Test if variable is a member of  */
Text t;                                /* given list of variables          */
List xs; {
    for (; nonNull(xs); xs=tl(xs))
	if (t==textOf(hd(xs)))
	    return hd(xs);
    return NIL;
}

Name nameIsMember(t,ns)			/* Test if name with text t is a   */
Text t;					/* member of list of names xs	   */
List ns; {
    for (; nonNull(ns); ns=tl(ns)) {
        if (t==name(hd(ns)).text) {
	    return hd(ns);
	}
    }
    return NIL;
}

/* Locating entities in import/export lists */

Name nameInIEList(nm,ns)		/* Test if Name is a member of */
Name nm;				/* of import/export list xs.   */
List ns; {
    Text t = name(nm).text;
    Bool isMethod = isClass(name(nm).parent);
    Bool isDCon   = isTycon(name(nm).parent) && !findTycon(name(nm).text);

    for (; nonNull(ns); ns=tl(ns)) {
        if (isName(hd(ns)) && t==name(hd(ns)).text) {
	    return hd(ns);
	}
        if ( (isMethod && isPair(hd(ns)) && isClass(fst(hd(ns)))) ||
	     (isDCon   && 
	      isPair(hd(ns)) && isTycon(fst(hd(ns))) && 
	      (tycon(fst(hd(ns))).what != SYNONYM)   &&
	      (tycon(fst(hd(ns))).what != RESTRICTSYN)) ) {
	  Name r;
	  List subs = snd(hd(ns));
	  if (subs == DOTDOT) {
	    if (isClass(fst(hd(ns)))) {
	      subs = cclass(fst(hd(ns))).members;
	    } else if (isTycon(fst(hd(ns)))) {
	      subs = tycon(fst(hd(ns))).defn;
	    }
	  }
	  r = nameInIEList(nm,subs);
	  if (r) return r;
	}
    }
    return NIL;
}



Tycon tyconInIEList(t,ns)   	       /* Test if Tycon with text t is a  */
Text t;				       /* member of import/export list xs */
List ns; {
  for (; nonNull(ns); ns=tl(ns)) {
    if (isTycon(hd(ns)) && t==tycon(hd(ns)).text) {
        return hd(ns);
    } else if (isPair(hd(ns)) && isTycon(fst(hd(ns))) &&
	       t == tycon(fst(hd(ns))).text) {
        return fst(hd(ns));       
    }
  }
  return NIL;
}

Class classInIEList(t,ns)   	       /* Test if Class with text t is a  */
Text t;				       /* member of import/export list xs */
List ns; {
  for (; nonNull(ns); ns=tl(ns)) {
    if (isClass(hd(ns)) && t==cclass(hd(ns)).text) {
        return hd(ns);
    }
    if (isPair(hd(ns)) && isClass(fst(hd(ns))) &&
	t == cclass(fst(hd(ns))).text) {
      return fst(hd(ns));       
    }
  }
  return NIL;
}

List nubList(ls)   /* (non-destructively) remove duplicates from list */
List ls; {
  List res = NIL;
  
  while (nonNull(ls)) {
    if (!cellIsMember(hd(ls),res)) {
      res = cons(hd(ls),res);
    }
    ls = tl(ls);
  }
  return res;
}

Cell intIsMember(n,xs)                 /* Test if integer n is member of   */
Int  n;                                /* given list of integers           */
List xs; {
    for (; nonNull(xs); xs=tl(xs))
	if (n==intOf(hd(xs)))
	    return hd(xs);
    return NIL;
}

Cell cellIsMember(x,xs)                /* Test for membership of specific  */
Cell x;                                /* cell x in list xs                */
List xs; {
    for (; nonNull(xs); xs=tl(xs))
	if (x==hd(xs))
	    return hd(xs);
    return NIL;
}

Cell cellAssoc(c,xs)	               /* Lookup cell in association list  */
Cell c; 	
List xs; {
    for (; nonNull(xs); xs=tl(xs))
	if (c==fst(hd(xs)))
	    return hd(xs);
    return NIL;
}

Cell cellRevAssoc(c,xs)	               /* Lookup cell in range of          */
Cell c; 			       /* association lists      	   */
List xs; {
    for (; nonNull(xs); xs=tl(xs))
	if (c==snd(hd(xs)))
	    return hd(xs);
    return NIL;
}

List replicate(n,x)			/* create list of n copies of x	   */
Int n;
Cell x; {
    List xs=NIL;
    while (0<n--)
	xs = cons(x,xs);
    return xs;
}

List diffList(from,take)               /* list difference: from\take       */
List from, take; {                     /* result contains all elements of  */
    List result = NIL;                 /* `from' not appearing in `take'   */

    while (nonNull(from)) {
	List next = tl(from);
	if (!cellIsMember(hd(from),take)) {
	    tl(from) = result;
	    result   = from;
	}
	from = next;
    }
    return rev(result);
}

List deleteCell(xs, y)                  /* copy xs deleting pointers to y  */
List xs;
Cell y; {
    List result = NIL; 
    for(;nonNull(xs);xs=tl(xs)) {
	Cell x = hd(xs);
	if (x != y) {
	    result=cons(x,result);
	}
    }
    return rev(result);
}

List take(n,xs)                         /* destructively truncate list to  */
Int  n;                                 /* specified length                */
List xs; {
    List ys = xs;

    if (n==0)
	return NIL;
    while (1<n-- && nonNull(xs))
	xs = tl(xs);
    if (nonNull(xs))
	tl(xs) = NIL;
    return ys;
}

List splitAt(n,xs)                         /* drop n things from front of list*/
Int  n;       
List xs; {
    for(; n>0; --n) {
	xs = tl(xs);
    }
    return xs;
}

Cell nth(n,xs)                         /* extract n'th element of list    */
Int  n;
List xs; {
    for(; n>0 && nonNull(xs); --n, xs=tl(xs)) {
    }
    if (isNull(xs))
	internal("nth");
    return hd(xs);
}

List removeCell(x,xs)                   /* destructively remove cell from  */
Cell x;                                 /* list                            */
List xs; {
    if (nonNull(xs)) {
	if (hd(xs)==x)
	    return tl(xs);              /* element at front of list        */
	else {
	    List prev = xs;
	    List curr = tl(xs);
	    for (; nonNull(curr); prev=curr, curr=tl(prev))
		if (hd(curr)==x) {
		    tl(prev) = tl(curr);
		    return xs;          /* element in middle of list       */
		}
	}
    }
    return xs;                          /* here if element not found       */
}

/* --------------------------------------------------------------------------
 * Operations on applications:
 * ------------------------------------------------------------------------*/

Int argCount;                          /* number of args in application    */

Cell getHead(e)                        /* get head cell of application     */
Cell e; {                              /* set number of args in argCount   */
    for (argCount=0; isAp(e); e=fun(e))
	argCount++;
    return e;
}

List getArgs(e)                        /* get list of arguments in function*/
Cell e; {                              /* application:                     */
    List as;                           /* getArgs(f e1 .. en) = [e1,..,en] */

    for (as=NIL; isAp(e); e=fun(e))
	as = cons(arg(e),as);
    return as;
}

Cell nthArg(n,e)                       /* return nth arg in application    */
Int  n;                                /* of function to m args (m>=n)     */
Cell e; {                              /* nthArg n (f x0 x1 ... xm) = xn   */
    for (n=numArgs(e)-n-1; n>0; n--)
	e = fun(e);
    return arg(e);
}

Int numArgs(e)                         /* find number of arguments to expr */
Cell e; {
    Int n;
    for (n=0; isAp(e); e=fun(e))
	n++;
    return n;
}

Cell applyToArgs(f,args)               /* destructively apply list of args */
Cell f;                                /* to function f                    */
List args; {
    while (nonNull(args)) {
	Cell temp = tl(args);
	tl(args)  = hd(args);
	hd(args)  = f;
	f         = args;
	args      = temp;
    }
    return f;
}

/* --------------------------------------------------------------------------
 * Handle table - declared here for the GC to access.
 * ------------------------------------------------------------------------*/

#if IO_HANDLES
#if WANT_FIXED_SIZE_TABLES
struct strHandle DEFTABLE(handles,NUM_HANDLES);
#else
DynTable* dynTabHandles = NULL;

struct strHandle *handles;
unsigned long     num_handles = 0;
#endif

/* --------------------------------------------------------------------------
 * Freeing a handle.
 * ------------------------------------------------------------------------*/
static Void local freeHandle(n)         /* release handle storage when no  */
Int n; {                                /* heap references to it remain    */
#if WANT_FIXED_SIZE_TABLES
    if (0<=n && n<(Int)NUM_HANDLES && nonNull(handles[n].hcell)) {
#else
    if (0<=n && n<(Int)num_handles && nonNull(handles[n].hcell)) {
#endif
	if (n>HSTDERR && handles[n].hmode!=HCLOSED && handles[n].hfp) {
	    fclose(handles[n].hfp);
	    handles[n].hfp = 0;
	}
	fst(handles[n].hcell) = snd(handles[n].hcell) = NIL;
	handles[n].hcell      = NIL;
    }
}
#endif

#if GC_MALLOCPTRS
/* --------------------------------------------------------------------------
 * Malloc Ptrs:
 * ------------------------------------------------------------------------*/

struct strMallocPtr mallocPtrs[NUM_MALLOCPTRS];

/* Points to the next available slot in 'mallocPtrs'. */
int mallocPtr_hw;

/* It might GC (because it uses a table not a list) which will trash any
 * unstable pointers.  
 * (It happens that we never use it with unstable pointers.)
 */
Cell newMallocPtr(ptr) 			/* create a new malloc pointer     */
Pointer ptr; {
    Int i;
    for (i=0; i<NUM_MALLOCPTRS && mallocPtrs[i].refCount!=0; ++i)
	;					/* Search for unused entry */
    if (i>=NUM_MALLOCPTRS) {			/* If at first we don't    */
	garbageCollect();			/* succeed, garbage collect*/
	for (i=0; i<NUM_MALLOCPTRS && mallocPtrs[i].refCount!=0; ++i)
	    ;					/* and try again ...	   */
    }
    if (i>=NUM_MALLOCPTRS) {			/* ... before we give up   */
	ERRMSG(0) "Too many ForeignPtrs open"
	EEND;
    }
    mallocPtrs[i].ptr      = ptr;
    mallocPtrs[i].finalizers = NIL;
    mallocPtrs[i].refCount = 1;

    /* adjust the high-water mark for the table. */
    if (i >= mallocPtr_hw) {
	mallocPtr_hw = i + 1;
    }
    return (mallocPtrs[i].mpcell = ap(MPCELL,i));
}

Cell mkMallocPtr(ptr,cleanup)            /* create a new malloc pointer    */
Pointer ptr;
CFinalizer cleanup; {
    Cell mp;
    Int i;
    mp = newMallocPtr(ptr);
    i = mpOf(mp);
    mallocPtrs[i].finalizers = cons(mkPtr((Pointer)cleanup), mallocPtrs[i].finalizers);
    return mp;
}

Void incMallocPtrRefCnt(n,i)             /* change ref count of MallocPtr */
Int n;
Int i; {	
    if (!(0<=n && n<NUM_MALLOCPTRS && mallocPtrs[n].refCount > 0))
	internal("freeMallocPtr");
    mallocPtrs[n].refCount += i;
    if (mallocPtrs[n].refCount <= 0) {
	Cell p;
	for (p=mallocPtrs[n].finalizers; nonNull(p); p=tl(p)) {
	    Cell fin = hd(p);
	    if (isPtr(fin))
		((CFinalizer)ptrOf(fin))(mallocPtrs[n].ptr);
	    else
		((CFinalizerEnv)ptrOf(fst(fin)))
		    (ptrOf(snd(fin)), mallocPtrs[n].ptr);
	}

	mallocPtrs[n].ptr      = 0;
	mallocPtrs[n].finalizers = NIL;
	mallocPtrs[n].refCount = 0;
	mallocPtrs[n].mpcell   = NIL;
	
	/* Freed the slot next to the high-water mark; adjust the marker. */
	if ((n+1) == mallocPtr_hw) {
	    do {
		--mallocPtr_hw;
	    } while (mallocPtr_hw>0 && isNull(mallocPtrs[mallocPtr_hw-1].mpcell));
	}
    }
}
#endif /* GC_MALLOCPTRS */

/* --------------------------------------------------------------------------
 * Stable pointers
 * This is a mechanism that allows the C world to manipulate pointers into the
 * Haskell heap without having to worry that the garbage collector is going
 * to delete it or move it around.
 * The implementation and interface is based on my implementation in
 * GHC - but, at least for now, is simplified by using a fixed size
 * table of stable pointers.
 * ------------------------------------------------------------------------*/

#if GC_STABLEPTRS

/* Each entry in the stable pointer table is either a heap pointer
 * or is not currently allocated.
 * Unallocated entries are threaded together into a freelist.
 * The last entry in the list contains the Cell 0; all other values
 * contain a Cell whose value is the next free stable ptr in the list.
 * It follows that stable pointers are strictly positive (>0).
 */
static Cell stablePtrTable[NUM_STABLEPTRS];
static Int  sptFreeList;
#define SPT(sp) stablePtrTable[(sp)-1]

static Void local resetStablePtrs() {
    Int i;
    /* It would be easier to build the free list in the other direction
     * but, when debugging, it's way easier to understand if the first
     * pointer allocated is "1".
     */
    for(i=1; i < NUM_STABLEPTRS; ++i)
	SPT(i) = i+1;
    SPT(NUM_STABLEPTRS) = 0;
    sptFreeList = 1;
}

Int mkStablePtr(c)                  /* Create a stable pointer            */
Cell c; {
    Int i = sptFreeList;
    if (i == 0)
	return 0;
    sptFreeList = SPT(i);
    SPT(i) = c;
    return i;
}

Cell derefStablePtr(p)              /* Dereference a stable pointer       */
Int p; {
    if (!(1 <= p && p <= NUM_STABLEPTRS)) {
	internal("derefStablePtr");
    }
    return SPT(p);
}

Void freeStablePtr(i)               /* Free a stable pointer             */
Int i; {
    SPT(i) = sptFreeList;
    sptFreeList = i;
}

#undef SPT
#endif /* GC_STABLEPTRS */

/* --------------------------------------------------------------------------
 * storage control:
 * ------------------------------------------------------------------------*/

#if DYN_TABLES
static void far* safeFarCalloc Args((Int,Int));
static void far* safeFarCalloc(n,s)     /* allocate table storage and check*/
Int n, s; {                             /* for non-null return             */
    void far* tab = farCalloc(n,s);
    if (tab==0) {
	ERRMSG(0) "Cannot allocate run-time tables"
	EEND;
    }
    return tab;
}
#define TABALLOC(v,t,n)                 v=(t far*)safeFarCalloc(n,sizeof(t));
#define TABFREE(v) free(v)
#else
#define TABALLOC(v,t,n)
#define TABFREE(v)
#endif

DynTable* allocDynTable(eltSize, maxIdx, hWater, tabName)
unsigned long eltSize;
unsigned long maxIdx;
unsigned long hWater;
const char* tabName; {
   DynTable *tab = (DynTable*)malloc(sizeof(struct strDynTable));
   
   if ( tab != NULL ) {
     tab->maxIdx  = maxIdx;
     tab->hWater  = hWater;
     tab->tabName = tabName;
     tab->eltSize = eltSize;
     tab->data    = (void*)malloc(eltSize * maxIdx);
   }
   
   if (tab == NULL || tab->data == NULL) {
       ERRMSG(0) "Cannot allocate dynamic table \"%s\"", tabName
       EEND;
   }
   return tab;
}

void freeDynTable(tab)
DynTable* tab; {
   if (tab) {
     free(tab->data);
     free(tab);
   }
   return;
}

void growDynTable(tab)
DynTable* tab; {
   unsigned long newSize;
   void*         newData;

   if ( tab == NULL )  {
       ERRMSG(0) "growDynTable: null table"
       EEND;
   }

   /* Are we already at the limit? */
   if ( tab->hWater != 0 && tab->maxIdx == tab->hWater ) {
       ERRMSG(0) "growDynTable: unable to grow table \"%s\" further (reached limit: %lu)", 
                 tab->tabName, tab->hWater
       EEND;
   }
   /* Growing currently means doubling. */   
    newSize = 2*tab->maxIdx;

    /* don't grow beyond hWater */
   if (tab->hWater != 0 && tab->hWater < newSize) {
     newSize = tab->hWater;
   } else if ( newSize == 0 ) {
     newSize = 1;
   }
#if 0
   fprintf(stderr, "growing \"%s\" from %d to %d elements\n", tab->tabName, tab->maxIdx, newSize);
   fflush(stderr); 
#endif
   newData = (void*)realloc(tab->data, newSize*tab->eltSize);
   
   if ( newData == NULL ) {
       ERRMSG(0) "growDynTable: unable to grow table \"%s\" (limit: %lu)", 
                 tab->tabName, tab->hWater
       EEND;
   } else {
     tab->maxIdx = newSize;
     tab->data   = newData;
   }
}


Void controlFuns(what)
Int what; {
    Int i;
    struct primInfoDef *info_def = firstPrimInfo;
    for(; 0 != info_def; info_def=info_def->nextPrimInfoDef) {
	if (info_def->p_info->controlFun) {
	    (*(info_def->p_info->controlFun))(what);
	}
    }

    if (EXIT == what) {
      struct primInfoDef *ptr, *tmp;

      /* Release all primitive DLLs */
      i = 0;
      while (i < scriptHw) {
	if (scripts[i].prims) {
	  freePrimInfo(scripts[i].prims);
	  scripts[i].prims = 0;
	}
	i++;
      }

      ptr = firstPrimInfo;
      while (ptr) {
	tmp = ptr->nextPrimInfoDef;
	free(ptr);
	ptr = tmp;
      }
      
#if !WANT_FIXED_SIZE_TABLES      
      if (dynTabScripts) freeDynTable(dynTabScripts);
#endif
    }
}

Void storage(what)
Int what; {
    Int i;

    switch (what) {
	case RESET   : clearStack();

		       /* the next 2 statements are particularly important
			* if you are using GLOBALfst or GLOBALsnd since the
			* corresponding registers may be reset to their
			* uninitialised initial values by a longjump.
			*/
		       heapTopFst = heapFst + heapSize;
		       heapTopSnd = heapSnd + heapSize;
#if PROFILING
		       heapTopThd = heapThd + heapSize;
		       if (profile) {
			   garbageCollect();
			   fclose(profile);
#if HAVE_HP2PS
			   system("hp2ps profile.hp");
#endif
			   profile = 0;
		       }
#endif
#if IO_HANDLES
		       handles[HSTDIN].hmode  = HREAD;
		       handles[HSTDIN].hbufMode = HUNKNOWN_BUFFERING;
		       handles[HSTDOUT].hmode = HAPPEND;
		       handles[HSTDOUT].hbufMode = HUNKNOWN_BUFFERING;
		       handles[HSTDERR].hmode = HAPPEND;
		       handles[HSTDERR].hbufMode = HUNKNOWN_BUFFERING;
#endif /* IO_HANDLES */
#if GC_STABLEPTRS
		       resetStablePtrs();
#endif
		       consGC = TRUE;
		       lsave  = NIL;
		       rsave  = NIL;
		       if (isNull(lastExprSaved))
			   savedText = NUM_TEXT;
		       break;

	case MARK    : 
		       start();
		       for (i=NAMEMIN; i<nameHw; ++i) {
			   mark(name(i).parent);
			   mark(name(i).defn);
			   mark(name(i).type);
			   mark(name(i).clashes);
		       }
		       end("Names", nameHw-NAMEMIN);
#if OBSERVATIONS
                       start();
                       for (i=OBSMIN; i<observeHw; ++i) mark(firstObs(observe(i).head));
                       end("Observations", observeHw=OBSMIN);
#endif
		       start();
		       for (i=MODMIN; i<moduleHw; ++i) {
			   mark(module(i).tycons);
			   mark(module(i).names);
			   mark(module(i).classes);
			   mark(module(i).exports);
			   mark(module(i).modImports);
			   mark(module(i).modAliases);
			   mark(module(i).qualImports);
		       }
		       end("Modules", moduleHw-MODMIN);

		       start();
		       for (i=TYCMIN; i<tyconHw; ++i) {
			   mark(tycon(i).defn);
			   mark(tycon(i).kind);
			   mark(tycon(i).what);
			   mark(tycon(i).clashes);
		       }
		       end("Type constructors", tyconHw-TYCMIN);

		       start();
		       for (i=CLASSMIN; i<classHw; ++i) {
			   mark(cclass(i).head);
			   mark(cclass(i).tyvars);
			   mark(cclass(i).kinds);
			   mark(cclass(i).fds);
			   mark(cclass(i).xfds);
			   mark(cclass(i).dsels);
			   mark(cclass(i).supers);
			   mark(cclass(i).members);
			   mark(cclass(i).defaults);
			   mark(cclass(i).instances);
			   mark(cclass(i).clashes);
		       }
		       mark(classes);
		       end("Classes", classHw-CLASSMIN);

		       start();
		       for (i=INSTMIN; i<instHw; ++i) {
			   mark(inst(i).head);
			   mark(inst(i).kinds);
			   mark(inst(i).specifics);
			   mark(inst(i).implements);
		       }
		       end("Instances", instHw-INSTMIN);

		       start();
		       for (i=0; i<=sp; ++i)
			   mark(stack(i));
		       end("Stack", sp+1);

		       start();
		       mark(lastExprSaved);
		       mark(lsave);
		       mark(rsave);
		       end("Last expression", 3);
#if IO_HANDLES
		       start();
		       mark(handles[HSTDIN].hcell);
		       mark(handles[HSTDOUT].hcell);
		       mark(handles[HSTDERR].hcell);
		       end("Standard handles", 3);
#endif

#if GC_STABLEPTRS
		       start();
		       for (i=0; i<NUM_STABLEPTRS; ++i)
			   mark(stablePtrTable[i]);
		       end("Stable pointers", NUM_STABLEPTRS);
#endif

#if GC_WEAKPTRS
		       mark(finalizers);
#endif

#if GC_MALLOCPTRS
		       for (i=0; i<mallocPtr_hw; ++i)
			   if (isPair(mallocPtrs[i].mpcell))
			       mark(mallocPtrs[i].finalizers);
#endif

		       if (consGC) {
			   start();
			   gcCStack();
			   end("C stack", stackRoots);
		       }

		       break;

	case INSTALL : heapFst = heapAlloc(heapSize);
		       heapSnd = heapAlloc(heapSize);

		       if (heapFst==(Heap)0 || heapSnd==(Heap)0) {
			   ERRMSG(0) "Cannot allocate heap storage (%d cells)",
				     heapSize
			   EEND;
		       }

		       heapTopFst = heapFst + heapSize;
		       heapTopSnd = heapSnd + heapSize;
#if PROFILING
		       heapThd = heapAlloc(heapSize);
		       if (heapThd==(Heap)0) {
			   ERRMSG(0) "Cannot allocate profiler storage space"
			   EEND;
		       }
		       heapTopThd   = heapThd + heapSize;
		       profile      = 0;
		       if (0 == profInterval)
			   profInterval = heapSize / DEF_PROFINTDIV;
#endif
		       for (i=1; i<heapSize; ++i) {
			   fst(-i) = FREECELL;
			   snd(-i) = -(i+1);
		       }
		       snd(-heapSize) = NIL;
		       freeList  = -1;
		       numGcs    = 0;
		       consGC    = TRUE;
		       lsave     = NIL;
		       rsave     = NIL;

		       marksSize  = bitArraySize(heapSize);
		       if ((marks=(Int *)calloc(marksSize, sizeof(Int)))==0) {
			   ERRMSG(0) "Unable to allocate gc markspace"
			   EEND;
		       }
		       
#if !WANT_FIXED_SIZE_TABLES
		       dynTabScripts = allocDynTable(sizeof(script),10,0,"scripts");
		       scripts = (script*)(dynTabScripts->data);
		       dynTabClass = allocDynTable(sizeof(struct strClass),10,NUM_CLASSES,"class");
		       tabClass = (struct strClass*)(dynTabClass->data);

		       dynTabInst = allocDynTable(sizeof(struct strInst),50,NUM_INSTS,"instance");
		       tabInst = (struct strInst*)(dynTabInst->data);
		       dynTabHandles = allocDynTable(sizeof(struct strHandle),4, 0, "handles");
		       handles = (struct strHandle*)(dynTabHandles->data);
		       num_handles = dynTabHandles->maxIdx;
#endif
		       TABALLOC(text,      char,             NUM_TEXT)
		       TABALLOC(tyconHash, Tycon,            TYCONHSZ)
		       TABALLOC(tabTycon,  struct strTycon,  NUM_TYCON)
		       TABALLOC(nameHash,  Name,             NAMEHSZ)
		       TABALLOC(tabName,   struct strName,   NUM_NAME)
		       TABALLOC(tabClass,  struct strClass,  NUM_CLASSES)
		       TABALLOC(cellStack, Cell,             NUM_STACK)
		       TABALLOC(tabModule, struct strModule, NUM_MODULE)
#if OBSERVATIONS
                       TABALLOC(tabObserve,struct strObserve, NUM_OBS_TAGS)
                       TABALLOC(tabBreakpt,struct strBreakpt, NUM_BRKPTS)
#endif
		       clearStack();

#if IO_HANDLES
		       TABALLOC(handles,   struct strHandle, NUM_HANDLES)
#if WANT_FIXED_SIZE_TABLES
		       for (i=0; i<(Int)NUM_HANDLES; i++)
#else
		       for (i=0; i<(Int)num_handles; i++)
#endif
			   handles[i].hcell = NIL;

		       handles[HSTDIN].hcell  = ap(HANDCELL,HSTDIN);
		       handles[HSTDIN].hfp    = stdin;
		       handles[HSTDOUT].hcell = ap(HANDCELL,HSTDOUT);
		       handles[HSTDOUT].hfp   = stdout;
		       handles[HSTDERR].hcell = ap(HANDCELL,HSTDERR);
		       handles[HSTDERR].hfp   = stderr;
#endif

		       textHw        = 0;
		       nextNewText   = NUM_TEXT;
		       nextNewDText  = (-1);
		       lastExprSaved = NIL;
		       savedText     = NUM_TEXT;
		       for (i=0; i<TEXTHSZ; ++i)
			   textHash[i][0] = NOTEXT;


		       addrHw   = 0;
#if OBSERVATIONS
                       observeHw = OBSMIN;
                       breakptHw = BRKMIN;
#endif

		       moduleHw = MODMIN;

		       tyconHw  = TYCMIN;
		       for (i=0; i<TYCONHSZ; ++i)
			   tyconHash[i] = NIL;

#if GC_WEAKPTRS
		       finalizers   = NIL;
		       liveWeakPtrs = NIL;
#endif
#if GC_MALLOCPTRS
		       /* The high-water mark for the table points at the
		        * next available slot in the table
		        */
		       mallocPtr_hw = 0;
		       for (i=0; i<NUM_MALLOCPTRS; i++)
			   mallocPtrs[i].mpcell = NIL;
#endif

#if GC_STABLEPTRS
		       resetStablePtrs();
#endif
		       nameHw	= NAMEMIN;
		       for (i=0; i<NAMEHSZ; ++i)
			   nameHash[i] = NIL;

		       classHw  = CLASSMIN;
		       instHw   = INSTMIN;

#if WANT_FIXED_SIZE_TABLES
		       tabInst  = (struct strInst far *)
				    farCalloc(NUM_INSTS,sizeof(struct strInst));

		       if (tabInst==0) {
			   ERRMSG(0) "Cannot allocate instance tables"
			   EEND;
		       }
#endif

		       scriptHw = 0;

		       break;
	case EXIT    : 
	               /* Let go of dynamic storage */
	               if (heapFst) free(heapFst);
	               if (heapSnd) free(heapSnd);
#if PROFILING
		       if (heapThd) free(heapThd);
#endif
#if !WANT_FIXED_SIZE_TABLES
		       if (dynTabClass)   freeDynTable(dynTabClass);
		       if (dynTabInst)    freeDynTable(dynTabInst);
		       if (dynTabHandles) freeDynTable(dynTabHandles);
#else
#endif
		       TABFREE(text);
		       TABFREE(tyconHash);
		       TABFREE(tabTycon);
		       TABFREE(nameHash);
		       TABFREE(tabName);
		       TABFREE(tabClass);
		       TABFREE(cellStack);
		       TABFREE(tabModule);
#if OBSERVATIONS
                       TABFREE(tabObserve);
                       TABFREE(tabBreakpt);
#endif
		       if (marks) free(marks);
		       
		       /* Note: primInfoDef memory is freed in controlFuns() above */

		       break;
    }
}

/*-------------------------------------------------------------------------*/
