Exports evaluateTagged's result type by name

changelog.d/pts-r69a.md

@@ -0,0 +1,3 @@
+### Added
+
+- `ProjectedEvaluation` on the `./tagged` subpath names what `evaluateTagged` answers; it is the main entry point's `EvaluateResult` without the `ParseError` arm, so every value of it is also an `EvaluateResult`, and no answer changes.

src/tagged.ts

@@ -44,6 +44,15 @@ import { isPlainMap, setKey } from "./maps.js";
 import { DEPTH_LIMIT, enterContainer, type PlaceCount, visitPlace } from "./nesting.js";
 import { Duration, Float, PDate, PDateTime, toHost, Undefined, type Value } from "./values.js";
 
+/**
+ * What `evaluateTagged` answers, named on this subpath so a host can write it.
+ * The main entry point's `EvaluateResult` is this type with a `ParseError` arm
+ * added, the arm a source text fails on; this entry point takes no source
+ * text, so it answers none, and every value of this type is also an
+ * `EvaluateResult`.
+ */
+export type { ProjectedEvaluation };
+
 /**
  * Why a text could not be decoded. `"depth_limit_exceeded"` is a text whose
  * brackets and braces nest past the depth limit this package declares.

test/export-surface.json

@@ -74,6 +74,7 @@
     "DecodeResult",
     "EncodeReason",
     "EncodeResult",
+    "ProjectedEvaluation",
     "TaggedEvaluateOptions",
     "TaggedExecution",
     "decodeTagged",

test/tagged.test.ts

@@ -1,12 +1,13 @@
 import { describe, expect, it } from "vitest";
-import { compileProgram, type EvaluateOptions } from "../src/index.js";
+import { compileProgram, type EvaluateOptions, type EvaluateResult } from "../src/index.js";
 import {
   type DecodeReason,
   decodeTagged,
   type EncodeReason,
   encodeTagged,
   evaluateTagged,
   executeTagged,
+  type ProjectedEvaluation,
   type TaggedEvaluateOptions,
   type TaggedExecution,
 } from "../src/tagged.js";
@@ -713,6 +714,18 @@ describe("evaluateTagged", () => {
     expect(outcome.error.type).toBe("UndefinedVariableError");
   });
 
+  // The answer has a name on this subpath, so a host holding one writes its
+  // type rather than reading it off the function, and the same value is one
+  // member of what the main entry point's `evaluate` answers. Sabotage:
+  // dropping the type's re-export from the subpath turns the export-surface
+  // pin red on its assertion and the typecheck stage red on this import.
+  it("answers the subpath's own evaluation result type", () => {
+    const outcome: ProjectedEvaluation = evaluateTagged([["load", "holds"]], { holds: 1 });
+    expect(outcome).toEqual({ ok: true, value: 1 });
+    const widened: EvaluateResult = outcome;
+    expect(widened).toBe(outcome);
+  });
+
   it("takes an options object written for the main entry point too", () => {
     const shared: EvaluateOptions = { onUnbound: "error" };
     const options: TaggedEvaluateOptions = { ...shared, tagged: true };