fix typing for #ap method

CHANGELOG.md

@@ -2,7 +2,7 @@ CHANGELOG
 =========
 
 ## HEAD (Unreleased)
-_(none)_
+* Fix typing for `#ap`
 
 ---
 

src/lib/randomator.spec.ts

@@ -109,7 +109,8 @@ describe('Randomator', () => {
 
   test('#ap', () => {
     const r$ = ab$.map(_ => _.toUpperCase());
-    expect(r$.ap('c')).toMatch(/C/);
+    const v = r$.ap('c');
+    expect(v).toMatch(/C/);
   });
 
   test('#ap throws on unmapped randomator', () => {

src/lib/randomator.test-d.ts

@@ -49,3 +49,12 @@ expectType<number>(j$());
 // toArray
 const k = e$.toArray(5);
 expectType<number[]>(k);
+
+// switchMap
+const l$ = e$.map(n => n + n);
+const m$ = l$.switchMap(a$);
+expectType<string>(m$());
+
+// ap
+const n = l$.ap(10);
+expectType<number>(n);

src/lib/randomator.ts

@@ -88,7 +88,7 @@ export class Randomator<T = unknown> extends Function implements Iterator<T> {
    * @param value A value
    * @returns
    */
-  ap<U>(value: unknown): U {
+  ap(value: unknown): T {
     const mapping = this[MappingFunction];
     if (!mapping) {
       throw new Error('ap can only be called on a mapped Randomator');