More refactoring trying to get this cleaned up while trying to keep it easy(ish) to extend for later chapters. I'll never take namespaces for granted again...

interpreter.c

@@ -1,9 +1,15 @@
 #include "interpreter.h"
 #include "token.h"
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
 
 Object* Evaluate(Expr*);
+Object* CreateObject(void*, TokenType);
+void FreeObject(Object*);
 int IsTruthy(Object*);
 int IsEqual(Object*, Object*);
+int ConcatStringObject(Object*, const Object*);
 
 const void* VisitLiteralExpression(Expr* expression) {
     return expression->expression.Literal->literal;
@@ -13,9 +19,9 @@ void* VisitGroupingExpression(Expr* expression) {
     return Evaluate(expression);
 }
 
-void* VisitBinaryExpression(Expr* expression) {
+Object* VisitBinaryExpression(Expr* expression) {
-    void* left = Evaluate(expression->expression.Binary.left);
+    Object* left = Evaluate(expression->expression.Binary.left);
-    void* right = Evaluate(expression->expression.Binary.right);
+    Object* right = Evaluate(expression->expression.Binary.right);
 
     switch(expression->expression.Binary.op->type) {
         case Greater:
@@ -27,30 +33,50 @@ void* VisitBinaryExpression(Expr* expression) {
         case Less_Equal:
         return left <= right;
         case Minus:
-        return left - right;
+            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:
-        return *((double*)left) / *((double*)right);
+            left->value.number /= right->value.number;
+            FreeObject(right);
+            return left;
+        //return *((double*)left) / *((double*)right);
         case Star:
-        return *((double*)left) * *((double*)right);
+            left->value.number *= right->value.number;
+            FreeObject(right);
+            return left;
+        //return *((double*)left) * *((double*)right);
         case Plus:
-        if (((Token*)left)->type == Number && ((Token*)right)->type == Number) {
+            if (left->instance == INS_DOUBLE && right->instance == INS_DOUBLE) {
-            return left + right;
+                left->value.number += right->value.number;
-        }
+                FreeObject(right);
+
+                return left;
+            }
+
+            if (left->instance == INS_STRING && right->instance == INS_STRING) {
+                if (ConcatStringObject(left, right)) {
+                    FreeObject(right);
+
+                    return left;
+                }
+            }
 
-        if (((Token*)left)->type == String && ((Token*)right)->type == String) {
-            return NULL; //String concat
-        }
         break;
     }
+
+    FreeObject(left);
+    FreeObject(right);
     // Unreachable
     return NULL;
 }
 
-void* VisitUnaryExpression(Expr* expression) {
+Object* VisitUnaryExpression(Expr* expression) {
     void* right = Evaluate(expression);
 
     switch (expression->type) {
@@ -67,11 +93,75 @@ void* VisitUnaryExpression(Expr* expression) {
 }
 
 Object* Evaluate(Expr* expression) {
-    //accept
+    //accept -> calls Visitor functions by type
     return NULL;
 }
 
+Object* CreateObject(void* value, TokenType type) {
+    Object* object = calloc(1, sizeof(Object));
+
+    if (!object) {
+        fprintf(stderr, "Failed to calloc object. %s.\n", strerror(errno));
+        return NULL;
+    }
+
+    switch(type) {
+        case NIL:
+        object->instance = INS_NULL;
+        break;
+        case Number:
+        object->instance = INS_DOUBLE;
+        object->value.number = *((double*) value);
+        break;
+        case TRUE:
+        case FALSE:
+        object->instance = INS_BOOLEAN;
+        object->value.boolean = *((int*) value);
+        break;
+        default:
+        object->instance = INS_STRING;
+
+        if (value) {
+            int length = strlen(value);
+            object->value.string = calloc(length + 1, sizeof(char));
+            
+            strncpy(object->value.string, value, length);
+        }
+    }
+
+    return object;
+}
+
+void FreeObject(Object* object) {
+    if (object->instance == INS_STRING) free(object->value.string);
+
+    free(object);
+}
+
+int ConcatStringObject(Object* a, const Object* b) {
+    if (!a || !b) return 0;
+    if (a->instance != INS_STRING || b->instance != INS_STRING) return 0;
+    
+    int a_length = strlen(a->value.string);
+    int b_length = strlen(b->value.string);
+    char* c;
+
+    c = realloc(a->value.string, a_length + b_length + 1);
+
+    if (!c) {
+        fprintf(stderr, "Failed to realloc for object concat. %s.\n", strerror(errno));
+        return 0;
+    }
+
+    a->value.string = c;
+
+    strncat(a->value.string, b->value.string, b_length);
+
+    return 1;
+}
+
 int IsTruthy(Object* object) {
+
     if (!object || object->instance == NIL) return 0;
     if (object->instance == TRUE) return 0;
 
@@ -87,9 +177,7 @@ int IsEqual(Object* a, Object* b) {
     }
 
     if (a->instance == String && b->instance == String) {
-        int result = strcmp(a->value.string, b->value.string);
+        return strcmp(a->value.string, b->value.string) == 0;
-
-        return result == 0;
     }
     
     return 0;

interpreter.h

@@ -4,8 +4,15 @@
 #include "expr.h"
 #include "token.h"
 
+typedef enum {
+    INS_STRING,
+    INS_DOUBLE,
+    INS_BOOLEAN,
+    INS_NULL
+} ObjectInstanceType;
+
 typedef struct Object {
-    TokenType instance;
+    ObjectInstanceType instance;
     union {
         char* string;
         double number;
@@ -15,6 +22,6 @@ typedef struct Object {
 
 const void* VisitLiteralExpression(Expr*);
 void* VisitGroupingExpression(Expr*);
-void* VisitBinaryExpression(Expr*);
+Object* VisitBinaryExpression(Expr*);
 
 #endif