Trying a more object oriented approach and created an 'Object' struct to have metadata for the values the interpreter works with.

interpreter.c

@@ -1,9 +1,9 @@
 #include "interpreter.h"
 #include "token.h"
 
-void* Evaluate(Expr*);
-int IsTruthy(void*);
-int IsEqual(void*, void*);
+Object* Evaluate(Expr*);
+int IsTruthy(Object*);
+int IsEqual(Object*, Object*);
 
 const void* VisitLiteralExpression(Expr* expression) {
     return expression->expression.Literal->literal;
@@ -66,22 +66,31 @@ void* VisitUnaryExpression(Expr* expression) {
     return NULL; //Should be unreachable.
 }
 
-void* Evaluate(Expr* expression) {
+Object* Evaluate(Expr* expression) {
     //accept
     return NULL;
 }
 
-int IsTruthy(void* object) {
-    if (!object) return 0;
-    if (*((int *) object) == 0) return 0;
+int IsTruthy(Object* object) {
+    if (!object || object->instance == NIL) return 0;
+    if (object->instance == TRUE) return 0;
 
     return 1;
 }
 
-int IsEqual(void* a, void* b) {
-    if (!a && !b) return 1;
-    if (!a) return 0;
+int IsEqual(Object* a, Object* b) {
+    if (a->instance == NIL && b->instance == NIL) return 1;
+    if (a->instance == NIL) return 0;
+
+    if (b->instance == Number && b->instance == Number) {
+        return a->value.number == b->value.number;
+    }
+
+    if (a->instance == String && b->instance == String) {
+        int result = strcmp(a->value.string, b->value.string);
+
+        return result == 0;
+    }
     
-    //Oh this'll be fun...
     return 0;
 }