* pmacros.scm (scan-list1): Reorganize tracing so that the tracing

	of a pmacro begins before its arguments are evaluated, improves
	readability.

diff --git a/ChangeLog b/ChangeLog
index 4b041dcf192d54ca76ce673f73f8912dfa044431..52c792c647f6d22d06f8d3df1778fb561655c24c 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2009-08-19  Doug Evans  <dje@sebabeach.org>
 
+       * pmacros.scm (scan-list1): Reorganize tracing so that the tracing
+       of a pmacro begins before its arguments are evaluated, improves
+       readability.
+
        * pmacros.scm (.sll, .srl, .sra): Fix thinko.
        * testsuite/pmacros-1.test: Ditto.  Add better tests.
 

diff --git a/pmacros.scm b/pmacros.scm
index b8ec407fd2d33f07e2c5e8b8327a4e6c00d10ed6..a45d8678e555cd2cc66558d76f13f3efc1366965 100644 (file)
--- a/pmacros.scm
+++ b/pmacros.scm
@@ -145,6 +145,10 @@
 (define (-smacro-set! name val) (hashq-set! -smacro-table name val))
 
 ; Marker to indicate a value is a pmacro.
+; NOTE: Naming this "<pmacro>" is intentional.  It makes them look like
+; objects of class <pmacro>.  However we don't use COS in part to avoid
+; a dependency on COS and in part because displaying COS objects isn't well
+; supported (displaying them in debugging dumps adds a lot of noise).
 (define -pmacro-marker '<pmacro>)
 
 ; Utilities to create and access pmacros.
@@ -358,48 +362,57 @@
     ;; Check for syntactic forms.
     ;; They are handled differently in that we leave it to the transformer
     ;; routine to evaluate the arguments.
+    ;; Note that we also don't support passing syntactic form functions
+    ;; as arguments: We look up (car exp) here, not its expansion.
     (let ((sform (-smacro-lookup (car exp))))
       (if sform
          (begin
            ;; ??? Is it useful to trace these?
            (-smacro-apply sform (cdr exp) env loc))
          ;; Not a syntactic form.
-         ;; Evaluate all the arguments first.
-         (let ((scanned-exp (map (lambda (e) (scan e loc))
-                                 exp)))
-           (let ((macro (check-pmacro scanned-exp)))
-             (if macro
-                 (begin
-                   ;; Trace expansion here, we know we have a pmacro.
+         ;; See if we have a pmacro.  Do this before evaluating all the
+         ;; arguments (even though we will eventually evaluate all the
+         ;; arguments before invoking the pmacro) so that tracing is more
+         ;; legible (we print the expression we're about to evaluate *before*
+         ;; we evaluate its arguments).
+         (let ((scanned-car (scan (car exp) loc)))
+           (if (-pmacro? scanned-car)
+               (begin
+                 ;; Trace expansion here, we know we have a pmacro.
+                 (if -pmacro-trace?
+                     (let ((src-props (source-properties exp))
+                           (indent (spaces (* 2 (length (location-list loc))))))
+                       ;; We use `write' to display `exp' to see strings quoted.
+                       (display indent cep)
+                       (display "Expanding: " cep)
+                       (write exp cep)
+                       (newline cep)
+                       (display indent cep)
+                       (display "      env: " cep)
+                       (write env cep)
+                       (newline cep)
+                       (if (not (null? src-props))
+                           (begin
+                             (display indent cep)
+                             (display " location: " cep)
+                             (display (source-properties-location->string src-props) cep)
+                             (newline cep)))))
+                 ;; Evaluate all the arguments before invoking the pmacro.
+                 (let* ((scanned-args (map (lambda (e) (scan e loc))
+                                           (cdr exp)))
+                        (result (if (procedure? (-pmacro-transformer scanned-car))
+                                    (-pmacro-apply scanned-car scanned-args)
+                                    (cons (-pmacro-transformer scanned-car) scanned-args))))
                    (if -pmacro-trace?
-                       (let ((src-props (source-properties exp))
-                             (indent (spaces (* 2 (length (location-list loc))))))
-                         ;; We use `write' to display `exp' to see strings quoted.
+                       (let ((indent (spaces (* 2 (length (location-list loc))))))
                          (display indent cep)
-                         (display "Expanding: " cep)
-                         (write exp cep)
-                         (newline cep)
-                         (display indent cep)
-                         (display "      env: " cep)
-                         (display env cep)
-                         (newline cep)
-                         (if (not (null? src-props))
-                             (begin
-                               (display indent cep)
-                               (display " location: " cep)
-                               (display (source-properties-location->string src-props) cep)
-                               (newline cep)))))
-                   (let ((result (if (procedure? (-pmacro-transformer macro))
-                                     (-pmacro-apply macro (cdr scanned-exp))
-                                     (cons (-pmacro-transformer macro) (cdr scanned-exp)))))
-                     (if -pmacro-trace?
-                         (let ((indent (spaces (* 2 (length (location-list loc))))))
-                           (display indent cep)
-                           (display "   result: " cep)
-                           (write result cep)
-                           (newline cep)))
-                     result))
-                 scanned-exp))))))
+                         (display "   result: " cep)
+                         (write result cep)
+                         (newline cep)))
+                   result))
+               ;; Not a pmacro.
+               (cons scanned-car (map (lambda (e) (scan e loc))
+                                      (cdr exp))))))))
 
   ;; Macro expand EXP which is known to be a non-null list.
   ;; LOC is the location stack thus far.