From fddfed044719c2e8d9664a007b214dacc8a0aa36 Mon Sep 17 00:00:00 2001
From: Felix Perktold <Felix.Perktold@student.uibk.ac.at>
Date: Tue, 23 Dec 2025 13:12:30 +0100
Subject: fix redefinition of symbols in env, cleanup

---
 Makefile   |  2 +-
 README.ORG |  1 +
 lisp.c     | 17 ++++++++++-------
 lisp.h     |  4 ++--
 4 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index 095a7ae..d6d3fae 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 LEX     = flex
 YACC    = bison
-CC      = gcc -g
+CC      = gcc -g -Wall -Werror
 CFLAGS  = -DYYDEBUG=1
 LIBS    = -lreadline -lfl -lm
 OBJS	= lisp.o lisp.tab.o lex.yy.o
diff --git a/README.ORG b/README.ORG
index 8969629..1ea05cf 100644
--- a/README.ORG
+++ b/README.ORG
@@ -6,3 +6,4 @@ using lex and yacc
 + [[https://en.wikipedia.org/wiki/S-expression][s-expressions]]
 + [[https://www.bowaggoner.com/writeups/jumpstart/flexbison/jumpstart_flexbison.pdf?utm_source][flex / bison jumpstart]]
 + [[https://github.com/Robert-van-Engelen/tinylisp/blob/main/tinylisp.pdf][tinylisp.pdf]]
++ [[https://w3.pppl.gov/info/readline/A_Short_Completion_Example.html][pppl.gov readline]]
diff --git a/lisp.c b/lisp.c
index df84b6f..1695ff7 100644
--- a/lisp.c
+++ b/lisp.c
@@ -35,7 +35,7 @@ value *make_string(const char *s) {
 	return val;
 }
 
-value *NIL = NULL;
+value *NIL;
 value *make_nil() {
 	if (!NIL) {
 		NIL = malloc(sizeof(value));
@@ -94,12 +94,11 @@ value *reverse(value *list) {
 	return reversed;
 }
 
-void *println_value(value *val){
+void println_value(value *val){
 	print_value(val);
 	printf("\n");
 }
-void *print_value(value *val){
-	char *str;
+void print_value(value *val){
 	switch (val->type) {
 		case VT_INT:
 			printf("%d", val->as.i);
@@ -159,8 +158,6 @@ void *print_value(value *val){
 		default:
 			printf("<unknown>\n");
 	}
-
-	return val;
 }
 
 env *env_create(env *parent) {
@@ -173,6 +170,12 @@ env *env_create(env *parent) {
 }
 
 env *env_define(env *e, const char *sym, value *val) {
+	//if symbol has been found, redefine
+	if (e->symbol && !strcmp(e->symbol, sym)) {
+		e->value = val;
+		return e;
+	}
+	//if not, find end of list and add new definition
 	if (e->next) {
 		return env_define(e->next, sym, val);
 	}
@@ -460,5 +463,5 @@ value *builtin_lt(env *e, value *args) {
 }
 
 int is_integer(double x) {
-    return floor(x) == x && isfinite(x);
+	return floor(x) == x && isfinite(x);
 }
diff --git a/lisp.h b/lisp.h
index bb4d3ae..45986a6 100644
--- a/lisp.h
+++ b/lisp.h
@@ -49,8 +49,8 @@ value *car(value *cons);
 value *cdr(value *cons);
 value *reverse(value *list);
 
-void *print_value(value *val);
-void *println_value(value *val);
+void print_value(value *val);
+void println_value(value *val);
 // environments, TODO: make this use hashtable
 // symbol->val
 typedef struct env {
-- 
cgit v1.2.3