fix: fix up type definitions for R.flatMap and AR.flatMap

Author: mobily

__tests__/Result/flatMap.test.ts

@@ -1,7 +1,28 @@
+import { expectType } from 'ts-expect'
 import { pipe, R } from '../..'
 
+class Error1 extends Error {}
+class Error2 extends Error {}
+
 describe('flatMap', () => {
   it('returns Error', () => {
+    expectType<R.Result<string, Error1 | Error2>>(
+      pipe(
+        R.fromNullable('test', new Error1()),
+        R.flatMap(value => {
+          return Math.random() < 0.5 ? R.Ok(value) : R.Error(new Error2())
+        }),
+      ),
+    )
+    expectType<R.Result<string, Error1>>(
+      pipe(
+        R.fromNullable('test', new Error1()),
+        R.flatMap(value => {
+          return Math.random() < 0.5 ? R.Ok(value) : R.Error(new Error1())
+        }),
+      ),
+    )
+
     expect(
       pipe(
         R.fromNullable('value', 'this is bad'),

src/AsyncResult/AsyncResult.ts

@@ -10,7 +10,7 @@ export declare function make<A, B = globalThis.Error>(
 export declare function flatMap<A, B, C, D = B>(
   promise: AsyncResult<A, B>,
   mapFn: (value: A) => AsyncResult<C, D>,
-): AsyncResult<C, D>
+): AsyncResult<C, B | D>
 
 export declare function fold<A, B, C, D = B>(
   promise: AsyncResult<A, B>,

src/AsyncResult/index.ts

@@ -23,10 +23,10 @@ export declare function map<A, B, C>(
 export declare function flatMap<A, B, C, D = B>(
   promise: AsyncResult<A, B>,
   mapFn: (value: A) => AsyncResult<C, D>,
-): AsyncResult<C, D>
+): AsyncResult<C, B | D>
 export declare function flatMap<A, B, C, D = B>(
   mapFn: (value: A) => AsyncResult<C, D>,
-): (promise: AsyncResult<A, B>) => AsyncResult<C, D>
+): (promise: AsyncResult<A, B>) => AsyncResult<C, B | D>
 export declare function fold<A, B, C, D = B>(
   promise: AsyncResult<A, B>,
   mapFn: (value: A) => Result<C, D>,

src/Result/Result.ts

@@ -46,7 +46,7 @@ export declare function fromPromise<A>(
 export declare function flatMap<A, B, C, D = B>(
   result: Result<A, B>,
   mapFn: (value: A) => Result<C, D>,
-): Result<C, D>
+): Result<C, B | D>
 export declare function map<A, B, C>(
   result: Result<A, B>,
   mapFn: (value: A) => C,

src/Result/index.ts

@@ -99,11 +99,11 @@ export declare function mapWithDefault<A, B, C>(
 export declare function flatMap<A, B, C, D = B>(
   result: Result<A, B>,
   mapFn: (value: A) => Result<C, D>,
-): Result<C, D>
+): Result<C, B | D>
 
 export declare function flatMap<A, B, C, D = B>(
   mapFn: (value: A) => Result<C, D>,
-): (result: Result<A, B>) => Result<C, D>
+): (result: Result<A, B>) => Result<C, B | D>
 
 /** Returns `value` if `result` is `Ok(value)`, otherwise, throws an exception. */