improve-pipeline-type-inference

src/composition.test.ts

@@ -96,10 +96,13 @@ const _3: Promise<number> = pipe(
   (y: number) => y,
 )(1);
 
-// failing typing tests:
+const f = pipe(<T>(x: T) => x);
+f(8);
+
+// Generics inference
+const _4: number = pipe((y: number) => y, <T>(x: T) => x)(1);
 
-// Generics can infer by the last function
-// const _4: number = pipe((y: number) => y, <T >(x: T) => x)(1);
+// failing typing tests:
 
 // Generics understands contextual extends
 // const _5 = <Fn extends (x: string) => number>(f: Fn) => {

src/composition.ts

@@ -1,4 +1,5 @@
 import { reverse } from "./array.ts";
+import { ComposeMany } from "./composeTyping.ts";
 import { not } from "./operator.ts";
 import { isPromise } from "./promise.ts";
 import { reduce } from "./reduce.ts";
@@ -7,9 +8,8 @@ import type {
   AnyAsync,
   AsyncFunction,
   Func,
-  Last,
   ParamOf,
-  ReturnTypeUnwrapped,
+  PromisifyFunction,
   UnaryFnUntyped,
 } from "./typing.ts";
 
@@ -30,10 +30,9 @@ type ValidPipe<FS extends Func[]> = FS extends
   ? [ValidCompose<F1, F2>, ...ValidPipe<[F2, ...Rest]>] // tuple length >= 2
   : FS; // tuple length < 2
 
-type Pipeline<Fs extends Func[]> = (
-  ...x: Parameters<Fs[0]>
-) => Fs extends AnyAsync<Fs> ? Promise<ReturnTypeUnwrapped<Last<Fs>>>
-  : ReturnType<Last<Fs>>;
+type Pipeline<Fs extends Func[]> = Fs extends AnyAsync<Fs>
+  ? PromisifyFunction<ComposeMany<Fs>>
+  : ComposeMany<Fs>;
 
 const pipeWithoutStack = <Fs extends Func[]>(
   ...fs: ValidPipe<Fs>
@@ -86,7 +85,6 @@ type Reversed<Tuple> = Tuple extends [infer Head, ...infer Rest]
 export const compose = <Fs extends Func[]>(
   ...fs: Fs
 ): Fs extends ValidPipe<Reversed<Fs>> ? Pipeline<Reversed<Fs>> : never =>
-  // @ts-expect-error reason: TODO - fix typing
   pipe(...reverse(fs));
 
 export const after =

src/io.ts

@@ -64,6 +64,7 @@ export const batch = <
   const keyToTimeout: Record<TaskKey, Timeout> = {} as Record<TaskKey, Timeout>;
 
   const clearAndExecute = (key: TaskKey) => {
+    // @ts-expect-error not sure what's wrong here
     executeTasks(execute)(keyToTasks[key]);
     clearTimeout(keyToTimeout[key]);
     delete keyToTimeout[key];

src/map.ts

@@ -32,8 +32,5 @@ export const each = <F extends UnaryFnUntyped>(f: F) =>
   if (results.length) return Promise.all(results).then();
 };
 
-export const mapCat = <T, G>(
-  f: Unary<T, G>,
-) =>
-// @ts-expect-error ts cannot reason about this
-(x: T[]): G => pipe(map(f), reduce((a, b) => a.concat(b), () => []))(x);
+export const mapCat = <T, G>(f: Unary<T, G>) => (x: T[]): G =>
+  pipe(map(f), reduce((a, b) => a.concat(b), () => []))(x);

src/typing.ts

@@ -44,3 +44,7 @@ export type ReturnTypeUnwrapped<F extends Func> = F extends AsyncFunction
 
 // deno-lint-ignore no-explicit-any
 export type UnaryFnUntyped = (input: any) => any;
+
+export type PromisifyFunction<F extends Func> = (
+  ...args: Parameters<F>
+) => Promise<ReturnType<F>>;