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Re: Getting source location information

From: Bruce Korb
Subject: Re: Getting source location information
Date: Wed, 30 Nov 2005 07:30:43 -0800
User-agent: KMail/1.7.1

On Wednesday 30 November 2005 06:44 am, Ludovic Courtès wrote:
> Bruce Korb <address@hidden> writes:
> > Because the file is mostly *NOT* scheme.
> I did say that you could use "Scheme constructs", "be it from Scheme
> o[r] C code".  In other words, you can either write `(read)' in a piece
> of Scheme code, or call `scm_read ()' from your C code: both are
> strictly equivalent (well, almost).
> The point is: do not rewrite what already exists because *this* is hard
> to maintain.
> Actually, what you want is `primitive-load' + `read' (which handles
> piggy-backing of source location information as I said).  It is true,
> however, that `primitive-load' (or, rather, `open-input-file') is not
> guaranteed to use `mmap ()' the way you do it currently[*].  So if you
> do want to make sure that the input file is `mmap'd the way you like,
> then you may want to write your own variant of `primitive-load' (see
> `libguile/load.c').
> In any case, I can hardly imagine how Guile itself could be more helpful
> than this.  ;-)


I am completely certain that this makes sense to you.  To me, it does
not.  If I call ``scm_read(port)'' I have to attach the input file
as a port.  That read function reads an s-expr.  How can that work if
the non-Scheme text in the file is not an s-expr?  I don't see another
function for getting text from a port.  Am I missing something?
Especially troubling is the phrase, "Any whitespace before the
next token is discarded."  I do not want tokenized input.  I want raw
text.  I have my own methods for determining when something needs
a Scheme evaluation.  I will certainly have a more authoritative idea
about what is discardable white space and what is not.  Here, take
a look at an example template file:

It is about halfway down, after the phrase "It looks something like this".
Oh, here it is anyway, but there is some discussion describing it on
that page:

   [+ AutoGen5 template h c +]
   [+ CASE (suffix) +][+
      ==  h  +]
   typedef enum {[+
      FOR list "," +]
           IDX_[+ (string-upcase! (get "list_element")) +][+
      ENDFOR list +] }  list_enum;

   extern const char* az_name_list[ [+ (count "list") +] ];

      ==  c  +]
   #include "list.h"
   const char* az_name_list[] = {[+
     FOR list "," +]
     ENDFOR list +] };[+

   ESAC +]

That example text contains 3 scheme phrases to be evaluated by Guile:

  (string-upcase! (get "list_element"))
  (count "list")

"get", "count" and "suffix" are my own functions defined in other ways.
The file name should be "list.tpl" in all cases and the line numbers
be 2, 6 and 9 respectively.  Everything else is handled by my program.
So, I can hardly imagine how Guile would be able to do what you say it
can.  Likely, I am just missing something, but nevertheless, it is
escaping me.  BTW, the expression on line 6 gets evaluated three times.
Each time, ``(get "list_element")'' returns a different value.  Likewise,
``(suffix)'' is evaluated twice and returns "h" the first time and "c"
the second time.

Sorry to be such a bother.  Thanks - Bruce

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