[PATCH] Per-module reader

[ludovic.courtes@laas.fr (Ludovic Courtès)]

Hi,

The patch below adds a `#:reader' keyword to `define-module' that allows
modules to specify the reader that should be used to interpret them:

  (define-module (the-module)
    #:reader the-reader-for-my-favorite-syntax)

This way, module implementors can decide to use whatever syntax variant
they prefer, while not having any side-effect on the code being read
from other files or modules.  For illustration, here is an example that
makes use of my `guile-reader' thing:

--8<---------------cut here---------------start------------->8---
(define-module (module-with-reader)
  #:reader (let* ((elisp-char-tr
		   (make-token-reader #\?
				      (token-reader-procedure
				       (standard-token-reader 'character)))))
	     (make-reader (cons elisp-char-tr
				(map standard-token-reader
				     '(whitespace
				       sexp string number colon-keyword
				       semicolon-comment
				       symbol-upper-case symbol-lower-case
				       quote-quasiquote-unquote)))))
  #:use-module (system reader))


(define-public (return-a-colon-keyword)
  :a-keyword!)

(define-public (return-an-elisp-character)
  ?a)
--8<---------------cut here---------------end--------------->8---

For the module user, things are completely transparent:

  $ guile -L .
  guile> (read-options) 
  (keywords #f positions)
  guile> (use-modules (module-with-reader))
  guile> (return-a-colon-keyword)
  #:a-keyword!
  guile> (return-an-elisp-character)
  #\a
  guile> (module-reader (resolve-module '(module-with-reader)))
  #<reader 301c2328>
  guile> (module-reader (current-module))
  #<primitive-procedure read>

The patch has a slight impact on `boot-9.scm' and `load.c'.  The
procedure `primitive-load' (which is called by `load-module') is
modified in order to switch to the current module's reader as soon as
the current module changes.

Feedback welcome!  ;-)

Thanks,
Ludovic.


ChangeLog entry for `libguile':

2005-10-13  Ludovic Courtès  <ludovic.courtes@laas.fr>

	* load.c (scm_primitive_load):  Switch to the current module's
	reader when the current module changes.

        * module.h (scm_module_index_reader):  New macro.
	(SCM_MODULE_READER):  New macro.


ChangeLog entry for `ice-9':

2005-10-13  Ludovic Courtès  <ludovic.courtes@laas.fr>

	* boot-9.scm (module-type):  New field `reader'.  Updated
	callers of `module-constructor'.
	(module-reader):   New procedure.
	(set-module-reader!):  New procedure.
	(process-define-module):  Handle the `#:reader' keyword.


Index: ice-9/boot-9.scm
===================================================================
RCS file: /cvsroot/guile/guile/guile-core/ice-9/boot-9.scm,v
retrieving revision 1.351
diff -u -B -b -p -r1.351 boot-9.scm
--- ice-9/boot-9.scm	31 Jul 2005 23:36:50 -0000	1.351
+++ ice-9/boot-9.scm	13 Sep 2005 12:28:08 -0000
@@ -1185,7 +1185,8 @@
   (make-record-type 'module
 		    '(obarray uses binder eval-closure transformer name kind
 		      duplicates-handlers duplicates-interface
-		      observers weak-observers observer-id)
+		      observers weak-observers observer-id
+		      reader)
 		    %print-module))
 
 ;; make-module &opt size uses binder
@@ -1221,7 +1222,8 @@
 					  uses binder #f #f #f #f #f #f
 					  '()
 					  (make-weak-value-hash-table 31)
-					  0)))
+					  0
+					  read)))
 
 	  ;; We can't pass this as an argument to module-constructor,
 	  ;; because we need it to close over a pointer to the module
@@ -1247,6 +1249,8 @@
 (define set-module-name! (record-modifier module-type 'name))
 (define module-kind (record-accessor module-type 'kind))
 (define set-module-kind! (record-modifier module-type 'kind))
+(define module-reader (record-accessor module-type 'reader))
+(define set-module-reader! (record-modifier module-type 'reader))
 (define module-duplicates-handlers
   (record-accessor module-type 'duplicates-handlers))
 (define set-module-duplicates-handlers!
@@ -2042,10 +2046,22 @@
 	  (call-with-deferred-observers
 	   (lambda ()
 	     (module-use-interfaces! module (reverse reversed-interfaces))
+	     ;; Evaluate the `#:reader' argument in the context of the module
+	     ;; being defined.
+	     (set-module-reader! module
+				 (eval (module-reader module) module))
 	     (module-export! module exports)
 	     (module-replace! module replacements)
 	     (module-re-export! module re-exports)))
 	  (case (car kws)
+	    ((#:reader)
+	     ;; The argument to `#:reader' will be evaluated eventually.
+	     (set-module-reader! module (cadr kws))
+	     (loop (cddr kws)
+		   reversed-interfaces
+		   exports
+		   re-exports
+		   replacements))
 	    ((#:use-module #:use-syntax)
 	     (or (pair? (cdr kws))
 		 (unrecognized kws))
@@ -2138,7 +2154,7 @@
 		    (set-car! (memq a (module-uses module)) i)
 		    (module-local-variable i sym))))))
     (module-constructor (make-hash-table 0) '() b #f #f name 'autoload #f #f
-			'() (make-weak-value-hash-table 31) 0)))
+			'() (make-weak-value-hash-table 31) 0 read)))
 
 ;;; {Compiled module}
 
Index: libguile/load.c
===================================================================
RCS file: /cvsroot/guile/guile/guile-core/libguile/load.c,v
retrieving revision 1.86
diff -u -B -b -p -r1.86 load.c
--- libguile/load.c	23 May 2005 19:57:20 -0000	1.86
+++ libguile/load.c	13 Sep 2005 12:28:08 -0000
@@ -82,15 +82,29 @@ SCM_DEFINE (scm_primitive_load, "primiti
     scm_call_1 (hook, filename);
 
   { /* scope */
+    SCM module = SCM_BOOL_F, reader = SCM_BOOL_F;
     SCM port = scm_open_file (filename, scm_from_locale_string ("r"));
     scm_frame_begin (SCM_F_FRAME_REWINDABLE);
     scm_i_frame_current_load_port (port);
 
     while (1)
       {
-	SCM form = scm_read (port);
+	SCM form;
+
+	if (scm_current_module () != module)
+	  {
+	    module = scm_current_module ();
+	    reader = SCM_MODULE_READER (module);
+	  }
+
+	if (reader == SCM_BOOL_F)
+	  form = scm_read (port);
+	else
+	  form = scm_call_1 (reader, port);
+
 	if (SCM_EOF_OBJECT_P (form))
 	  break;
+
 	scm_primitive_eval_x (form);
       }
 
Index: libguile/modules.h
===================================================================
RCS file: /cvsroot/guile/guile/guile-core/libguile/modules.h,v
retrieving revision 1.28
diff -u -B -b -p -r1.28 modules.h
--- libguile/modules.h	31 Jul 2005 23:36:14 -0000	1.28
+++ libguile/modules.h	13 Sep 2005 12:28:08 -0000
@@ -45,6 +45,7 @@ SCM_API scm_t_bits scm_module_tag;
 #define scm_module_index_binder		2
 #define scm_module_index_eval_closure	3
 #define scm_module_index_transformer	4
+#define scm_module_index_reader        12
 
 #define SCM_MODULE_OBARRAY(module) \
   SCM_PACK (SCM_STRUCT_DATA (module) [scm_module_index_obarray])
@@ -56,6 +57,8 @@ SCM_API scm_t_bits scm_module_tag;
   SCM_PACK (SCM_STRUCT_DATA (module)[scm_module_index_eval_closure])
 #define SCM_MODULE_TRANSFORMER(module) \
   SCM_PACK (SCM_STRUCT_DATA (module)[scm_module_index_transformer])
+#define SCM_MODULE_READER(module) \
+  SCM_PACK (SCM_STRUCT_DATA (module)[scm_module_index_reader])
 
 SCM_API scm_t_bits scm_tc16_eval_closure;
 


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