Re: Designing Lisp from scratch

On Fri, Mar 23, 2007 at 07:22:48AM -0500, Shriram Krishnamurthi wrote:
> >I guess the main reason you may have a hard time finding lex/yacc
> >parsers for Lisp is that Lisp parsers are built into every Lisp system.
> >Thus, if you want to parse Lisp code, you just use Lisp and say (read).
> 
> Bzzzt.
> 
> READ does not *parse*.  Parsing is regarded as the process of
> distinguishing valid terms from invalid terms, accounting for the
> context-sensitive (and more) constraints of the language.  What READ
> does is..."read": it produces an intermediate language of terms that
> do not fully perform this distinction: that is, a term rejected by
> READ is illegal, but one not rejected may also be illegal.  E.g.: The
> following terms are not valid Scheme (or perhaps they are in some
> bizarre Scheme, but pretend they aren't):
> 
>  (lambda (x))
>  (define (f 5) 3)
> 
> but they do pass READ.  It is some other tool, the parser, that
> distinguishes these from the valid terms of the language.  This tool
> is hidden from the user of most Scheme systems.

Hmm. Would it not be valid to call what READ does "parsing" and what 
this "other tool" does semantic analysis?

Regards,

Bob

-- 
The reward for a job well done is more work.

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)

iD8DBQFGA90jfb9wcmD+WN4RAgcHAJ9XEN7ue3KNiZSD1QPSSWJuDweZ9ACgtppf
7xBAAyEpkHFgaCwsEZPhxjo=
=ab2Y
-----END PGP SIGNATURE-----