Started to try to get back into this; work on exceptions and loops.

src/memory/conspage.c

@@ -148,7 +148,7 @@ void free_cell( struct cons_pointer pointer ) {
                     dec_ref( cell->payload.cons.cdr );
                     break;
                 case EXCEPTIONTV:
-                    dec_ref( cell->payload.exception.message );
+                    dec_ref( cell->payload.exception.payload );
                     dec_ref( cell->payload.exception.frame );
                     break;
                 case FUNCTIONTV:

src/memory/consspaceobject.c

@@ -163,7 +163,7 @@ struct cons_pointer make_exception( struct cons_pointer message,
 
     inc_ref( message );
     inc_ref( frame_pointer );
-    cell->payload.exception.message = message;
+    cell->payload.exception.payload = message;
     cell->payload.exception.frame = frame_pointer;
 
     result = pointer;

src/memory/consspaceobject.h

@@ -45,7 +45,8 @@
 #define CONSTV      1397641027
 
 /**
- * An exception.
+ * An exception. TODO: we need a means of dealing with different classes of
+ * exception, and we don't have one yet.
  */
 #define EXCEPTIONTAG "EXEP"
 
@@ -108,6 +109,17 @@
  */
 #define LAMBDATV   1094995276
 
+/**
+ * A loop exit is a special kind of exception which has exactly the same
+ * payload as an exception.
+ */
+#define LOOPXTAG    "LOOX"
+
+/**
+ * The string `LOOX`, considered as an `unsigned int`.
+ */
+#define LOOPXTV     1481592652
+
 /**
  * The special cons cell at address {0,0} whose car and cdr both point to
  * itself.
@@ -286,10 +298,15 @@
 #define keywordp(conspoint) (check_tag(conspoint,KEYTAG))
 
 /**
- * true if `conspoint` points to a special Lambda cell, else false
+ * true if `conspoint` points to a Lambda binding cell, else false
  */
 #define lambdap(conspoint) (check_tag(conspoint,LAMBDATAG))
 
+/**
+ * true if `conspoint` points to a loop exit exception, else false.
+ */
+#define loopexitp(conspoint) (check_tag(conspoint,LOOPXTAG))
+
 /**
  * true if `conspoint` points to a special form cell, else false
  */
@@ -414,8 +431,8 @@ struct cons_payload {
  * Message should be a Lisp string; frame should be a pointer to an (unfreed) stack frame.
  */
 struct exception_payload {
-  /** The message: should be a Lisp string but in practice anything printable will do. */
-    struct cons_pointer message;
+  /** The payload: usually a Lisp string but in practice anything printable will do. */
+    struct cons_pointer payload;
   /** pointer to the (unfreed) stack frame in which the exception was thrown. */
     struct cons_pointer frame;
 };

src/memory/stack.c

@@ -267,7 +267,8 @@ void dump_frame( URL_FILE * output, struct cons_pointer frame_pointer ) {
 
 void dump_stack_trace( URL_FILE * output, struct cons_pointer pointer ) {
     if ( exceptionp( pointer ) ) {
-        print( output, pointer2cell( pointer ).payload.exception.message );
+    // todo: if the payload isn't a message, we maybe shouldn't print it?
+        print( output, pointer2cell( pointer ).payload.exception.payload );
         url_fputws( L"\n", output );
         dump_stack_trace( output,
                           pointer2cell( pointer ).payload.exception.frame );