1 files changed, 29 insertions, 2 deletions
diff --git a/clox/src/vm.c b/clox/src/vm.c
index df9f490..fae0092 100644
--- a/clox/src/vm.c
+++ b/clox/src/vm.c
@@ -1,9 +1,12 @@
 #include <stdarg.h>
 #include <stdio.h>
+#include <string.h>
 
 #include "common.h"
 #include "compiler.h"
 #include "debug.h"
+#include "memory.h"
+#include "object.h"
 #include "vm.h"
 
 VM vm;
@@ -43,6 +46,20 @@ static bool isFalsey(Value value) {
   return IS_NIL(value) || (IS_BOOL(value) && !AS_BOOL(value));
 }
 
+static void concatenate() {
+  ObjString *b = AS_STRING(pop());
+  ObjString *a = AS_STRING(pop());
+
+  int length = a->length + b->length;
+  char *chars = ALLOCATE(char, length + 1);
+  memcpy(chars, a->chars, a->length);
+  memcpy(chars + a->length, b->chars, b->length);
+  chars[length] = '\0';
+
+  ObjString *result = takeString(chars, length);
+  push(OBJ_VAL(result));
+}
+
 static InterpretResult run() {
 #define READ_BYTE() (*vm.ip++)
 #define READ_CONSTANT() (vm.chunk->constants.values[READ_BYTE()])
@@ -96,9 +113,19 @@ static InterpretResult run() {
     case OP_LESS:
       BINARY_OP(BOOL_VAL, <);
       break;
-    case OP_ADD:
-      BINARY_OP(NUMBER_VAL, +);
+    case OP_ADD: {
+      if (IS_STRING(peek(0)) && IS_STRING(peek(1))) {
+        concatenate();
+      } else if (IS_NUMBER(peek(0)) && IS_NUMBER(peek(1))) {
+        double b = AS_NUMBER(pop());
+        double a = AS_NUMBER(pop());
+        push(NUMBER_VAL(a + b));
+      } else {
+        runtimeError("Operands must be two numbers or two strings.");
+        return INTERPRET_RUNTIME_ERROR;
+      }
       break;
+    }
     case OP_SUBTRACT:
       BINARY_OP(NUMBER_VAL, -);
       break;