Reorg

src/lang/eval/value.ts

@@ -0,0 +1,73 @@
+import { Expr, FieldName, ProductPattern, Tag, VariableName } from "../expr";
+import { ThrownRuntimeError } from "./error";
+
+export type Value =
+  | { tag: "string", value: string }
+  | { tag: "number", value: number }
+  | { tag: "tag", tag_name: Tag  }
+  | { tag: "tagged", tag_name: Tag, value: Value }
+  | { tag: "tuple", values: Value[] }
+  | { tag: "record", fields: Map<FieldName, Value> }
+  | { tag: "closure", closure: Closure }
+
+export type ValueTag =
+  | "string"
+  | "number"
+  | "tag"
+  | "tagged"
+  | "tuple"
+  | "record"
+  | "closure"
+
+// Used as a Stack of frames. Basically a linked list.
+export type Env =
+  | { tag: "nil" }
+  | { tag: "frame", frame: EnvFrame, parent: Env }
+
+export type EnvFrame = Map<VariableName, Value>;
+
+export type Closure = {
+  env: Env,
+  parameters: ProductPattern[],
+  body: Expr,
+}
+
+export namespace Value {
+  export const string = (value: string): Value => ({ tag: "string", value });
+  export const number = (value: number): Value => ({ tag: "number", value });
+  export const tag = (tag_name: Tag): Value => ({ tag: "tag", tag_name });
+  export const tagged = (tag_name: Tag, value: Value): Value => ({ tag: "tagged", tag_name, value });
+  export const tuple = (values: Value[]): Value => ({ tag: "tuple", values });
+  export const record = (fields: Map<FieldName, Value>): Value => ({ tag: "record", fields });
+  export const closure = (closure: Closure): Value => ({ tag: "closure", closure });
+}
+
+export namespace Env {
+  export function nil(): Env {
+    return { tag: "nil" };
+  }
+  
+  export function push_frame(env: Env, frame: EnvFrame): Env {
+    return { tag: "frame", frame, parent: env };
+  }
+
+  // may throw `ThrownRuntimeError`
+  export function lookup(env: Env, var_name: VariableName): Value {
+    let cur = env;
+    while (cur.tag !== "nil") {
+      if (cur.frame.has(var_name)) {
+        return cur.frame.get(var_name)!;
+      }
+      cur = cur.parent;
+    }
+    throw ThrownRuntimeError.error({
+      tag: "VariableLookupFailure",
+      name: var_name,
+    });
+  }
+
+  export function frame_insert_mut(frame: EnvFrame, var_name: VariableName, value: Value) {
+     frame.set(var_name, value);
+  }
+}
+