Creating an object of type Boolean should work correctly, as long as the Boolean value being passed is done so as a double*.

interpreter.c

@@ -1,6 +1,7 @@
 #include "interpreter.h"
 #include "token.h"
 #include <errno.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -25,22 +26,22 @@ Object* VisitBinaryExpression(Expr* expression) {
 
     switch(expression->expression.Binary.op->type) {
         case Greater:
-        return left > right;
+        //return left > right;
         case Greater_Equal:
-        return left >= right;
+        //return left >= right;
         case Less:
-        return left < right;
+        //return left < right;
         case Less_Equal:
-        return left <= right;
+        //return left <= right;
+        case Bang_Equal:
+        //return !IsEqual(left, right);
+        case Equal_Equal:
+        //return IsEqual(left, right);
         case Minus:
             left->value.number -= right->value.number;
             FreeObject(right);
             return left;
         //return left - right;
-        case Bang_Equal:
-        return !IsEqual(left, right);
-        case Equal_Equal:
-        return IsEqual(left, right);
         case Slash:
             left->value.number /= right->value.number;
             FreeObject(right);
@@ -68,6 +69,10 @@ Object* VisitBinaryExpression(Expr* expression) {
             }
 
         break;
+        default:
+        FreeObject(left);
+        FreeObject(right);
+        return NULL; //Should be unreachable.
     }
 
     FreeObject(left);
@@ -77,18 +82,30 @@ Object* VisitBinaryExpression(Expr* expression) {
 }
 
 Object* VisitUnaryExpression(Expr* expression) {
-    void* right = Evaluate(expression);
+    Object* right = Evaluate(expression);
+    Object* c;
+    double computed_value;
 
-    switch (expression->type) {
+    switch (expression->expression.Unary.op->type) {
         case Minus:
+        computed_value = -right->value.number;
+        FreeObject(right);
+        c = CreateObject(&computed_value, Number);
         //right needs to be negated, but that kind of introduces a
         //memory leak since we can't really change it, what with the 
-        //whole "const void*" thing and all.        
-        return right;
+        //whole "const void*" thing and all.
+        return c;
         case Bang:
-        return !IsTruthy(right);
+        computed_value = !IsTruthy(right);
+        FreeObject(right);
+        c = CreateObject(&computed_value, TRUE); //TRUE or FALSE, doesn't matter here since it becomes INS_BOOLEAN in the end.
+        return c;
+        default:
+        FreeObject(right);
+        return NULL; //Should be unreachable.
     }
 
+    FreeObject(right);
     return NULL; //Should be unreachable.
 }
 
@@ -111,22 +128,21 @@ Object* CreateObject(void* value, TokenType type) {
         break;
         case Number:
         object->instance = INS_DOUBLE;
-        object->value.number = *((double*) value);
+        object->value.number = *(double*) value;
         break;
         case TRUE:
         case FALSE:
         object->instance = INS_BOOLEAN;
-        object->value.boolean = *((int*) value);
+        object->value.boolean = *(double*) value;
         break;
         default:
-        object->instance = INS_STRING;
-
         if (value) {
             int length = strlen(value);
+            object->instance = INS_STRING;
             object->value.string = calloc(length + 1, sizeof(char));
             
             strncpy(object->value.string, value, length);
-        }
+        } else object->instance = INS_NULL; //TODO: this is most likely an error, but we'll ignore that for now.
     }
 
     return object;
@@ -154,6 +170,7 @@ int ConcatStringObject(Object* a, const Object* b) {
     }
 
     a->value.string = c;
+    a->value.string[a_length + b_length] = '\0';
 
     strncat(a->value.string, b->value.string, b_length);