From 360fde205647a63765ac191464602422d9355b15 Mon Sep 17 00:00:00 2001
From: Ian Piumarta <piumarta@gmail.com>
Date: Mon, 27 Jan 2025 09:38:27 +0900
Subject: [PATCH] improve error message for invalid assignments

---
 demofiles/invalid-pointer.c | 18 +++++++++++++-----
 main.leg                    | 14 ++++++++++----
 2 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/demofiles/invalid-pointer.c b/demofiles/invalid-pointer.c
index ffad489..9d6f65b 100644
--- a/demofiles/invalid-pointer.c
+++ b/demofiles/invalid-pointer.c
@@ -4,9 +4,17 @@
 #include <stdint.h>
 
 int main() {
-  int *ptr = (int *)(intptr_t)0xDeadD0d0;
-  printf("%p\n",ptr);
-  *ptr = 42; 	// illegal memory access
-  printf("%d\n", *ptr);
-  return 0;
+    int i, *ptr;
+
+    ptr = &i;
+    printf("%p\n",ptr);
+    *ptr = 42;			// legal memory access
+    printf("%d\n", *ptr);
+
+    ptr = (int *)(intptr_t)0xDeadD0d0;
+    printf("%p\n",ptr);
+    *ptr = 42;			// illegal memory access
+    printf("%d\n", *ptr);
+
+    return 0;
 }
diff --git a/main.leg b/main.leg
index bcfef6b..7272b92 100644
--- a/main.leg
+++ b/main.leg
@@ -1,6 +1,6 @@
 # main.leg -- C parser + interpreter
 #
-# Last edited: 2025-01-26 21:27:29 by piumarta on zora
+# Last edited: 2025-01-27 09:37:11 by piumarta on zora
 
 %{
 ;
@@ -2163,7 +2163,8 @@ oop eval(oop exp, oop env)
 	    break;
 	}
 	case Assign: {
-	    oop lhs = get(exp, Assign,lhs);
+	    oop dst = get(exp, Assign,lhs);
+	    oop lhs = dst;
 	    oop rhs = eval(get(exp, Assign,rhs), nil);
 	    switch (getType(lhs)) {
 		case Symbol: {
@@ -2185,9 +2186,14 @@ oop eval(oop exp, oop env)
 		    }
 		    break;
 		}
-		default:	break;
+		default:
+		    break;
 	    }
-	    fatal("cannot assign to: %s", toString(lhs));
+	    if (dst == lhs)
+		fatal("cannot assign to: %s", toString(lhs));
+	    else
+		fatal("invalid rvalue '%s' assigning to: %s",
+		      toString(lhs), toString(dst));
 	    break;
 	}
 	case Cast: {