gpgscm: Keep a history of calls for error messages.

* tests/gpgscm/init.scm (vm-history-print): New function.
* tests/gpgscm/opdefines.h: New opcodes 'CALLSTACK_POP', 'APPLY_CODE',
and 'VM_HISTORY'.
* tests/gpgscm/scheme-private.h (struct history): New definition.
(struct scheme): New field 'history'.
* tests/gpgscm/scheme.c (gc): Mark objects in the history.
(history_free): New function.
(history_init): Likewise.
(history_mark): Likewise.
(add_mod): New macro.
(sub_mod): Likewise.
(tailstack_clear): New function.
(callstack_pop): Likewise.
(callstack_push): Likewise.
(tailstack_push): Likewise.
(tailstack_flatten): Likewise.
(callstack_flatten): Likewise.
(history_flatten): Likewise.
(opexe_0): New variable 'callsite', keep track of the expression if it
is a call, implement the new opcodes, record function applications in
the history.
(opexe_6): Implement new opcode.
(scheme_init_custom_alloc): Initialize history.
(scheme_deinit): Free history.
* tests/gpgscm/scheme.h (USE_HISTORY): New macro.
--

This patch makes TinySCHEME keep a history of function calls.  This
history can be used to produce helpful error messages.  The history
data structure is inspired by MIT/GNU Scheme.

Signed-off-by: Justus Winter <justus@g10code.com>

fu history

tests/gpgscm/init.scm

@@ -534,6 +534,28 @@
      `(define ,(cadr form)
           (call/cc (lambda (return) ,@(cddr form)))))
 
+;; Print the given history.
+(define (vm-history-print history)
+  (let loop ((n 0) (skip 0) (frames history))
+    (cond
+     ((null? frames)
+      #t)
+     ((> skip 0)
+      (loop 0 (- skip 1) (cdr frames)))
+     (else
+      (let ((f (car frames)))
+	(display n)
+	(display ": ")
+	(let ((tag (get-tag f)))
+	  (unless (null? tag)
+		  (display (basename (car tag)))
+		  (display ":")
+		  (display (+ 1 (cdr tag)))
+		  (display ": ")))
+	(write f))
+	(newline)
+	(loop (+ n 1) skip (cdr frames))))))
+
 ;;;; Simple exception handling
 ;
 ;    Exceptions are caught as follows: