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Should psyntax pass through a compiled VM program?

From: Neil Jerram
Subject: Should psyntax pass through a compiled VM program?
Date: Sun, 13 Sep 2009 22:17:34 +0100
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux)

I think that's the right eventual question, anyway.  The context is
running Alan Grover's mod_lisp-for-guile in 1.9.2.

The mod_lisp-for-guile code includes a use of read-hash-extend to
define a syntax for a compiled regular expression - so that you can
write things like

  (if (#m/^Error: +/ line)

with a similar effect to Perl

  if (line ~= /^Error: +/)


  (read-hash-extend #\m (lambda (c port)
                          (lambda (string)

In other words, the custom reader procedure returns another
procedure.  So the read code (for the above example) becomes

  (if (#<procedure (string)> line)

In pre-VM Guile, (I assume) this worked because there wasn't a psyntax
pass, and because the evaluator regards procedures as self-evaluating.

But in VM Guile, the read code is

  (if (#<program ...> line)

And psyntax errors when it hits the #<program>.

I've worked around this by rewriting the read-hash-extend code as

  (define-public (make-regexp-fn regexp-string)
    (lambda (string)

  (read-hash-extend #\m (lambda (c port)
                          `(make-regexp-fn ,regexp-string)))

but I wonder if there is a case for supporting the code as it was
before, by

- teaching psyntax to pass through a #<program> if it sees one

- making programs self-evaluating (and in fact they may already be so,
  I haven't checked).

Also, is it definitely correct to call read-hash-extend procedures
first, and do the psyntax pass later?  I guess it must be, as we need
to call the read-hash-extend procedure in order even to determine the
extent of the relevant lexeme.


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