add branching

1 files changed, 15 insertions, 0 deletions

diff --git a/src/lang/js-lang/builtin/builtin.ts b/src/lang/js-lang/builtin/builtin.ts
index dde91b6..d54c439 100644
--- a/src/lang/js-lang/builtin/builtin.ts
+++ b/src/lang/js-lang/builtin/builtin.ts
@@ -31,9 +31,24 @@ export const V_BUILTIN_Mul: BUILTIN = (args) => {
   );
 };
 
+export const V_BUILTIN_IfElse: BUILTIN = (args) => {
+  if (args.length !== 3) {
+    throw new Error(`Invalid args for "if": ${JSON.stringify(args)}`);
+  }
+
+  const [cond, trueVal, falseVal] = args;
+
+  if (typeof cond !== "boolean") {
+    throw new Error(`Condition value ${JSON.stringify(cond)} is not a boolean`);
+  }
+
+  return cond ? trueVal : falseVal;
+};
+
 export const nameToBUILTIN: Record<string, BUILTIN> = {
   arr: V_BUILTIN_Arr,
   tostring: V_BUILTIN_ToString,
   add: V_BUILTIN_Add,
   mul: V_BUILTIN_Mul,
+  "?": V_BUILTIN_IfElse,
 };