From 2b1f2e8e5790b4bc517ac9a56a0676d07e532929 Mon Sep 17 00:00:00 2001
From: Justin Ethier <justin.ethier@gmail.com>
Date: Tue, 27 Sep 2016 22:34:37 -0400
Subject: [PATCH] Issue #111 - Improve output of error messages

---
 icyc.scm  |  8 ++++++--
 runtime.c | 13 +++++++++++--
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/icyc.scm b/icyc.scm
index 36bfd1cf..424333a1 100644
--- a/icyc.scm
+++ b/icyc.scm
@@ -38,14 +38,18 @@
           (display "Error: ")
           (cond
             ((pair? obj)
+             (when (string? (car obj))
+               (display (car obj))
+               (display ": ")
+               (set! obj (cdr obj)))
              (for-each
                (lambda (o)
-                 (display o)
+                 (write o)
                  (display " "))
                obj))
             (else
               (display obj)))
-          (display "\n")
+          (newline)
           (k #t))
         (lambda ()
           (repl)))))
diff --git a/runtime.c b/runtime.c
index 8316b528..760f9ec5 100644
--- a/runtime.c
+++ b/runtime.c
@@ -423,6 +423,7 @@ object Cyc_glo_eval_from_c = NULL;
 object Cyc_default_exception_handler(void *data, int argc, closure _,
                                      object err)
 {
+  int is_msg = 1;
   fprintf(stderr, "Error: ");
 
   if ((err == NULL) || is_value_type(err) || type_of(err) != pair_tag) {
@@ -431,8 +432,16 @@ object Cyc_default_exception_handler(void *data, int argc, closure _,
     // Error is list of form (type arg1 ... argn)
     err = cdr(err);             // skip type field
     for (; (err != NULL); err = cdr(err)) {     // output with no enclosing parens
-      Cyc_display(car(err), stderr);
-      fprintf(stderr, " ");
+      if (is_msg && 
+          is_object_type(car(err)) && 
+          type_of(car(err)) == string_tag) {
+        is_msg = 0;
+        Cyc_display(car(err), stderr);
+        fprintf(stderr, ": ");
+      } else {
+        Cyc_write(car(err), stderr);
+        fprintf(stderr, " ");
+      }
     }
   }