Fix multiple-value-bind for single value forms

A form like f(values, 1, 2, 3)

doesn't actually need to call values so we can't just use it as a
continuation. We need to wrap everything with mvbind to check if
values is called or not.

  mvbind(values => f(values, 1, 2, 3), (x,y)=>...)

packages/delisp-core/__tests__/eval.ts

@@ -143,7 +143,7 @@ describe("Evaluation", () => {
     });
 
     it("multiple-value-bind can catch forms with a single value transparently", () => {
-      expect(evaluateString(`(multiple-value-bind (x) 3 x)`)).toBe(3);
+      expect(evaluateString(`(multiple-value-bind (x) 3 (+ x 1))`)).toBe(4);
     });
 
     it("multiple-value-bind can catch forms with a multiple values", () => {

packages/delisp-core/src/compiler.ts

@@ -387,11 +387,7 @@ function compileMultipleValueBind(
     compileBody(expr.node.body, newenv, multipleValues)
   );
 
-  return {
-    type: "CallExpression",
-    callee: form,
-    arguments: [continuation]
-  };
+  return primitiveCall("mvbind", form, continuation);
 }
 
 function compileUnknown(
@@ -532,7 +528,8 @@ function compileRuntimeUtils(
     "primaryValue",
     "values",
     "mvbind",
-    "bindPrimaryValue"
+    "bindPrimaryValue",
+    "mvbind"
   ]);
 }
 

packages/delisp-core/src/eval.ts

@@ -16,7 +16,8 @@ import {
   snd,
   values,
   primaryValue,
-  bindPrimaryValue
+  bindPrimaryValue,
+  mvbind
 } from "@delisp/runtime";
 
 export function createContext() {
@@ -31,7 +32,8 @@ export function createContext() {
     snd,
     values,
     primaryValue,
-    bindPrimaryValue
+    bindPrimaryValue,
+    mvbind
   };
   vm.createContext(sandbox);
   return sandbox;

packages/delisp-runtime/src/index.ts

@@ -72,3 +72,23 @@ export const values = primaryValue;
 export function bindPrimaryValue(fn: Function): Function {
   return (...args: unknown[]) => fn(primaryValue, ...args);
 }
+
+export function mvbind(
+  form: (values: any, ...args: any[]) => any,
+  cont: (...results: any[]) => any
+) {
+  let valuesCalled = false;
+
+  const values = (...results: any[]) => {
+    valuesCalled = true;
+    return cont(...results);
+  };
+
+  const result = form(values);
+
+  if (valuesCalled) {
+    return result;
+  } else {
+    return values(result);
+  }
+}