# Dictionary handling

The unit [mem/dict.fs] contains a few words that are useful to play around with
dictionary structures.

By "entry", we mean the address of the LL "next" field for the dictionary entry.
By "word", we mean the executable address of the entry. Remember: xt>e
translates an execution token to an entry, e>xt translates an entry into an
execution token.

Some of the words documented here actually live in kernel and [xcomp/boot.fs],
but because of their thematic affinity, are here.

## API

### Constants

ENTRYSZ
  The maximum length of a dictionary entry, excluding the name. We say "maximum"
  because the actual number of bytes depends on alignment constraints.

### Words

'e ( "x" -- e )
  Find entry x in system dictionary and error out if not found.
  Does not apply "find selector" logic [doc/usage/word].

' ( "x" -- xt )
  Find entry x in system dictionary and error out if not found. Yields the
  associated execution token (e>xt).

['] ( "x" -- ) *I*
  Find x and compile its address as a literal.

e>xt ( e -- xt )
  Yield an execution token from an entry.

e>wlen ( e -- a )
  Yield the address of "e"'s length field.

entrylen ( e -- n )
  Yield the length of the name of "e".

entrytag ( e -- n )
  Yield the tag (garbage number if untagged) associated with entry.
  See [doc/usage/tag].

sysdict ( -- e )
  Same as "SYSDICT @".

current ( -- xt )
  Yield the xt of the last word to be added to the system dictionary.

entryname[] ( entry -- a u )
  Yields the range containing "entry"'s name.

entry[] ( 'dict a u -- )
  Create entry with name corresponding to range "a u" in dictionary 'dict.

entry ( 'dict str -- )
  Shortcut for "c@+ entry[]".

reserveentry ( 'dict str payloadsz -- )
  Like "entry", but before creating an entry, reserves the size of the enntry
  added to "payloadsz" to ensure that they will both be contiguous.

findentry ( name 'dict -- entry-or-0 )
  Find name in dictionary pointer 'dict and yield the found entry or 0 if no
  match was found.

  Does not apply "find selector" logic [doc/usage/word].

find ( name 'dict -- xt-or-0 )
  Call "findentry" and yield the xt associated with the found entry.

find# ( name 'dict -- xt )
  Same as "find", but abort with "word not found" if not found.

findtagged ( tag name 'dict -- entry-or-0 )
  Call "findentry" then, if an entry is found, check that "entrytag" matches
  "tag". If yes, yield the entry. Otherwise, yield 0.

.word ( xt -- )
  Print "word"'s name.

words ( -- )
  Print all word name of the dictionary.

delete ( "name" -- )
  Find "name" and makes the entry unfindeable by setting its length to 0.

forget ( "name" -- )
  Find "name" in the dictionary and bring back the sysdict to the word that
  precedes it.

  This is different from the traditional Forth's "forget", which also rewinds
  "here". In Dusk, rewinding "here" is too tricky, tons of things can go wrong.
  Therefore, "forget" reclaims no memory. It merely tidies up the sysdict.

dictlink ( "name" -- )
  Create a new "Dictionary link", as described in doc/arch, named "name".
  Whenever you want to hold an entry reference without having to dereference
  held value before passing it to "find", you should use a dictlink rather than
  a simple "create" to avoid the possibility of a false match.

extractdict ( "lastword" "dictname" -- )
  Remove the top entries from sysdict up to "lastword" (inclusively), then
  create a new dictlink "dictname" with those entries that were removed.
  Example usage:

  : foo ;
  : bar ;
  : baz ;
  extractdict bar mydict
  \ "foo" stays in sysdict, "bar" and "baz" are removed. "mydict" is created
  \ with 2 entries, "bar" and "baz".

unitofentry ( e -- unit-or-0 )
  Look in all loaded units to see if entry "e" is part of one. If yes, yield
  it. That "unit" is a dict entry (for example, you can call "entryname[]" on
  it).

?xt>e ( a -- e-or-0 )
  Checks whether address "a" is the payload of a word, that is:

  1. Whether it's in "here" space or kernel space (memory can be read without
     breaking the system).
  2. Whether length byte is nonzero.
  3. Whether all characters in the name are in the range $21-7e.

  If all conditions are met, yield the associated entry. Otherwise, yield 0.

xt>e# ( a -- e )
  Calls ?xt>e and aborts with error message if 0.
