add createFn

1 files changed, 39 insertions, 0 deletions

diff --git a/src/lang/js-lang/builtin/builtin.ts b/src/lang/js-lang/builtin/builtin.ts
new file mode 100644
index 0000000..dde91b6
--- /dev/null
+++ b/src/lang/js-lang/builtin/builtin.ts
@@ -0,0 +1,39 @@
+type BUILTIN = (args: any[]) => any;
+
+export const V_BUILTIN_Arr: BUILTIN = (args) => args;
+
+// FIXME actually implement this properly
+export const V_BUILTIN_ToString: BUILTIN = (args) =>
+  args.length === 1 ? JSON.stringify(args[0]) : JSON.stringify(args);
+
+export const V_BUILTIN_Add: BUILTIN = (args) => {
+  if (args.every((arg) => ["string", "number"].includes(typeof arg))) {
+    return args.reduce(
+      (acc, cur) => acc + cur,
+      typeof args[0] === "string" ? "" : 0
+    );
+  }
+
+  throw new Error(`Cannot add operands ${JSON.stringify(args, undefined, 2)}`);
+};
+
+export const V_BUILTIN_Mul: BUILTIN = (args) => {
+  if (args.every((arg) => typeof arg === "number") && args.length === 2) {
+    return args.reduce((acc, cur) => acc * cur, 1);
+  }
+
+  throw new Error(
+    `Can only multiply [number, number], but got ${JSON.stringify(
+      args,
+      undefined,
+      2
+    )}`
+  );
+};
+
+export const nameToBUILTIN: Record<string, BUILTIN> = {
+  arr: V_BUILTIN_Arr,
+  tostring: V_BUILTIN_ToString,
+  add: V_BUILTIN_Add,
+  mul: V_BUILTIN_Mul,
+};