1 files changed, 102 insertions, 0 deletions
diff --git a/src/lang/ts-lang/core/eval.ts b/src/lang/ts-lang/core/eval.ts
new file mode 100644
index 0000000..5f22299
--- /dev/null
+++ b/src/lang/ts-lang/core/eval.ts
@@ -0,0 +1,102 @@
+import {
+  BUILTIN_Add,
+  BUILTIN_Arr,
+  BUILTIN_Mul,
+  BUILTIN_ToString,
+  SBUILTIN_Call,
+  SBUILTIN_Map,
+} from "../builtin";
+import { ToString } from "../util";
+import { ASTNode, EmptyStackFrame, NodeType, StackFrame } from "./common";
+
+export type SENTINEL_NO_BUILTIN = "__NO_BUILTIN__";
+export type MapBuiltins<
+  Node extends ASTNode,
+  Frame extends StackFrame
+> = GetEvaluatedChildren<Node, Frame> extends infer Args extends readonly any[]
+  ? Node["name"] extends "call"
+    ? SBUILTIN_Call<Node, Frame>
+    : Node["name"] extends "map"
+    ? SBUILTIN_Map<Node, Frame>
+    : Node["name"] extends "tostring"
+    ? BUILTIN_ToString<Args>
+    : Node["name"] extends "arr"
+    ? BUILTIN_Arr<Args>
+    : Node["name"] extends "add"
+    ? BUILTIN_Add<Args>
+    : Node["name"] extends "mul"
+    ? BUILTIN_Mul<Args>
+    : SENTINEL_NO_BUILTIN
+  : never;
+
+export type EvalError<T extends string> = `Eval error: ${T}`;
+
+export type FindInStack<
+  Frame extends StackFrame,
+  NameToFind
+> = NameToFind extends keyof Frame["bindings"]
+  ? Frame["bindings"][NameToFind]
+  : Frame["parent"] extends null
+  ? EvalError<`Can't find name "${ToString<NameToFind>}" on the stack`>
+  : FindInStack<Frame["parent"], NameToFind>;
+
+export type FnPrim<
+  Args extends readonly ASTNode[] = readonly ASTNode[],
+  Fn extends ASTNode = ASTNode
+> = { args: Args; fn: Fn };
+
+export type HandleFn<Node extends ASTNode> = Node["children"] extends [
+  ...infer Args extends ASTNode[],
+  infer Fn extends ASTNode
+]
+  ? FnPrim<Args, Fn>
+  : // error?
+    never;
+
+// any[] was propertykey
+export type MapZip<
+  Args extends readonly ASTNode[],
+  Values extends readonly any[]
+> = {
+  [Idx in Exclude<
+    keyof Args,
+    keyof any[]
+  > as Args[Idx] extends infer Node extends ASTNode
+    ? Node["name"]
+    : never]: Idx extends keyof Values ? Values[Idx] : never;
+};
+
+export type CallFn<
+  Fn extends FnPrim,
+  Values extends readonly any[],
+  Frame extends StackFrame
+> = _Evaluate<Fn["fn"], StackFrame<MapZip<Fn["args"], Values>, Frame>>;
+
+export type _Evaluate<
+  Node extends ASTNode,
+  Frame extends StackFrame
+> = Node["type"] extends NodeType.INT
+  ? Node["value"]
+  : Node["type"] extends NodeType.EXT
+  ? // special builtin
+    Node["name"] extends "fn"
+    ? HandleFn<Node>
+    : MapBuiltins<Node, Frame> extends infer BI
+    ? BI extends SENTINEL_NO_BUILTIN
+      ? FindInStack<Frame, Node["name"]>
+      : BI
+    : never
+  : EvalError<`Unhandled node type ${Node["type"]}`>;
+
+export type GetEvaluatedChildren<
+  Node extends ASTNode,
+  Frame extends StackFrame
+> = Node["children"] extends infer Children extends readonly ASTNode[]
+  ? {
+      [Idx in keyof Children]: Children[Idx] extends ASTNode
+        ? _Evaluate<Children[Idx], Frame>
+        : never;
+    }
+  : never;
+
+export type Evaluate<Node extends ASTNode> = _Evaluate<Node, EmptyStackFrame>;