2 files changed, 27 insertions, 2 deletions

diff --git a/pez.c b/pez.c
index 92f9a47..87cf518 100644
--- a/pez.c
+++ b/pez.c
@@ -2220,6 +2220,22 @@ f_arraypush(PezContext *cx, int argc)
     return push(cx, box_obj(arr));
 }
 
+static bool
+f_assert(PezContext *cx, int argc)
+{
+    TRY(pez_checksig(cx, argc, "assert", "any, ?string"));
+    if (!pez_truthy(cx, -argc)) {
+        char buf[8];
+        if (argc == 2)
+            pez_error(cx, "assert", "assertion failed: %s", pez_getstring(cx, buf, -1));
+        else
+            pez_error(cx, "assert", "assertion failed!");
+        return 0;
+
+    }
+    return pez_pushvoid(cx);
+}
+
 static const struct coredef { const char *n; PezCFn *f; } core[] = {
     { "printf", f_printf },
     { "sprintf", f_sprintf },
@@ -2227,6 +2243,7 @@ static const struct coredef { const char *n; PezCFn *f; } core[] = {
     { "typeof", f_typeof },
     { "array#new", f_arraynew },
     { "array#push", f_arraypush },
+    { "assert", f_assert },
 };
 
 static bool
@@ -4307,6 +4324,12 @@ pez_isarray(PezContext *cx, int idx)
     return isobj_of1(cx, idx, PEZ_TArray);
 }
 
+bool
+pez_truthy(PezContext *cx, int idx)
+{
+    return truthy(*iget(cx, idx));
+}
+
 int
 pez_typeof(PezContext *cx, int idx)
 {
@@ -4382,7 +4405,7 @@ pez_checksig(PezContext *cx, int argc, const char *fn, const char *sig)
             else assert(0 && "bad sig type");
             if (arg >= argc) {
                 if (opt) {
-                    break;
+                    goto next;
                 } else {
                     return pez_error(cx, fn, "too few args for [%s] (got %d)", osig, argc), 0;
                 }
@@ -4394,9 +4417,10 @@ pez_checksig(PezContext *cx, int argc, const char *fn, const char *sig)
         } while (*sig && *sig != ',');
         if ((typ & mask) == 0) {
             pez_error(cx, fn, "arg #%d mismatch: expected %.*s, got %s",
-                      arg, thisn, this, pez_typename(cx, -argc + arg));
+                      arg, thisn, this + !aisalpha(*this), pez_typename(cx, -argc + arg));
             return 0;
         }
+    next:
         sig += *sig == ',';
         if (!*sig) {
             ++arg;
diff --git a/pez.h b/pez.h
index 2330f1b..075eb41 100644
--- a/pez.h
+++ b/pez.h
@@ -70,6 +70,7 @@ bool pez_isbool(PezContext *, int idx);
 bool pez_isstring(PezContext *, int idx);
 bool pez_isfunction(PezContext *, int idx);
 bool pez_isarray(PezContext *, int idx);
+bool pez_truthy(PezContext *, int idx);
 int pez_typeof(PezContext *, int idx);
 const char *pez_typename(PezContext *, int idx);