Allow void return type

backend_wat.go

@@ -338,6 +338,10 @@ func compileFunctionWAT(function ParsedFunction) (string, error) {
 		returnTypes = function.ReturnType.Value.(TupleType).Types
 	}
 
+	if function.ReturnType.Type == Type_Void {
+		returnTypes = []Type{}
+	}
+
 	for _, t := range returnTypes {
 		funcWAT += "\t(result " + getWATType(t) + ")\n"
 	}

example/add.lang

@@ -2,6 +2,14 @@ u64 add(u8 a, u8 b) {
 	return add(a - 1u8, a);
 }
 
+u64 add2(u64 a, u64 b) {
+	return a + b;
+}
+
+void a() {
+
+}
+
 (u8, u8) doNothing(u8 a, u8 b) {
 	return a, b;
 }