improve car, cadr error handling

1 files changed, 14 insertions, 5 deletions

diff --git a/lisp.c b/lisp.c
index e111c47..f107bea 100644
--- a/lisp.c
+++ b/lisp.c
@@ -66,16 +66,25 @@ value *cons(value *car, value *cdr) {
 }
 
 value *car(value *cons) {
-	//TODO: more robust implementation with error catching
-	return cons->as.pair.car;
+	if (cons->type == VT_PAIR) {
+		return cons->as.pair.car;
+	}
+	printf("not a pair: ");
+	print_value(cons);
+	printf("\n");
+	return make_nil();
 }	
 
 value *cdr(value *cons) {
-	//TODO: more robust implementation with error catching
-	return cons->as.pair.cdr;
+	if (cons->type == VT_PAIR) {
+		return cons->as.pair.cdr;
+	}
+	printf("not a pair: ");
+	print_value(cons);
+	printf("\n");
+	return make_nil();
 }	
 
-
 void *print_value(value *val){
 	char *str;
 	switch (val->type) {