Subj : Re: Compiler and an interpreter
To   : comp.programming
From : Rob Thorpe
Date : Sun Jul 31 2005 01:08 pm

spinoza1111@yahoo.com wrote:
> Rob Thorpe wrote:
> > anjali wrote:
> > > Suppose in a source-code file, the 4th line contains the first syntax
> > > error.Can anybody please tell me how the compiler and interpreter will
> > > behave when the given file will be the input to them?
> > >
> > > My guess is that the compiler will go through the entire file and will
> > > report all the syntax errors in the file while the interpreter will
> > > stop its execution exactly after the 4th line and will say that there
> > > is a syntax error in the 4th line.
> >
> > This depends on the formal structure of the language and the design of
> > the compiler/interpreter.
> >
> > For the purposes of this discussion languages can be split into two
> > types, in which either:
> > 1. Only a complete file/module is an acceptable input
> > 2. Some small unit of the language is an acceptable input.
> >
> > C, C++ and Pascal are example of type 1, there are many more.
> > Bash, lisp and ML are examples of type 2, again there are many more.
> >
> > If the language is of type 1 then the compiler/interpreter must read
> > the whole file/module before beginning to do anything with it in
> > earnest.  In doing so it will find any syntax errors.
> >
> > If the language is of type 2 then the compiler/interpreter can begin to
> > act on the input as it's going along.  A compiler may do this by
> > writing out machine code, an interpreter may do this by performing the
> > actions specified.
> >
> > The compiler/interpreter doesn't have to be written this way though, it
> > may choose to do nothing with the input until it reaches the end of the
> > file/module.
> >
> > Most compilers read the entire input file before writing out code.
> > Many interpreters act of input a line at a time.  But not all, Perl for
> > example reads the whole file before beginning to execute it.
>
> It is not even grammatical to say, where X is the name of a programming
> language, that X "reads the whole file before beginning to execute it",
> and more than it is grammatical to say "Cobol goes to the corner bar
> and has a drink".
>
> Yet programmers continue to use this ugly syntax! As if programming
> languages were active agents! This practise is a reification, a
> fetishization and it hypostasizes mere artifacts into things that
> REPLACE the very idea of human agency, and contribute in fact to
> alienation.
>
> Perl does not to my knowledge in any way require the reading of the
> entire Perl file. But even if it does, it isn't correct to say "Perl
> reads". Perl is a language and not a compiler.

Yes, I should have said "perl" referring to the program perl rather
than the language "Perl".  Or stated that I was referring to the
implementation perl.

> I just don't know if it is possible to write Incremental Perl or
> Incremental C in the manner of a Lisp interpreter such that the
> following earth shattering exchange could take place in Perl or C as it
> can in Lisp.
>
> >7
>
> 7
>
> (user types 7 which evaluates, details at 11, to 7.)
>
> But it might be since so many things in C and Perl are expressions with
> a value:
>
> >"Hello world"
> Hello world
> >"Bnarg"
> Bnarg
> >bnarg // undefined
> VOID
>
> The last exchange shows that an Incremental C could never be standard
> since a language in which it is the general practice to read the entire
> file (a requirement given the otiose preprocessor) is also a language
> that doesn't permit undefined identifiers.

Yes, AFAIK you can't write an incremental implementation of standard C,
there have been incremental C implementations but they haven't been
standard.

You might be able to write an incremental Perl interpreter, I don't
know.  Since the language doesn't have a standard whatever perl the
program does is often taken as the standard.

.