feat: reducers

BREAKING CHANGE: countInIterable, everyInIterable and someInIterable have been removed, use
reduceIterable instead

README.md

@@ -64,6 +64,12 @@ How-to:
 
 - **Get a flag indicating if the element is the first element:** `zipIterables(firstIterable, yourIterable)` (returns an iterable of `[boolean, <element>]`).
 
+- **Count elements in an iterable:**: `applyPipe(yourIterable, reduceIterable(countReducer, 0))`.
+
+- **Check if every element in an iterable is true:** `applyPipe(yourIterableOfBooleans, reduceIterable(andReducer, true))` (iteration will not continue unnecessarily because of how [`reduceIterable`](https://github.com/ivan7237d/antiutils/blob/master/src/internal/iterable/reduceIterable.ts) and [`andReducer`](https://github.com/ivan7237d/antiutils/blob/master/src/internal/reducer/andReducer.ts) are defined).
+
+- **Check if some elements in an iterable are true:** `applyPipe(yourIterableOfBooleans, reduceIterable(orReducer, false))`.
+
 - **Find the first element matching a predicate:** `applyPipe(yourIterable, filter(yourPredicate), firstInIterable)`.
 
 - **Yield values while a condition holds:**
@@ -75,7 +81,7 @@ How-to:
   );
   ```
 
-  (yields `1`, `2`, see [`scanIterable`](https://github.com/ivan7237d/antiutils/blob/master/src/internal/iterable/scanIterable.ts) and [`reduceIterable`](https://github.com/ivan7237d/antiutils/blob/master/src/internal/iterable/reduceIterable.ts)).
+  (yields `1`, `2`, see [`scanIterable`](https://github.com/ivan7237d/antiutils/blob/master/src/internal/iterable/scanIterable.ts)).
 
 - **Also yield the value that broke the condition:**
 
@@ -114,6 +120,12 @@ It [provides](https://github.com/ivan7237d/antiutils/tree/master/src/internal/co
 
 It also provides implementations of `EqualFunction` for objects, iterables, maps, and sets, and a function [`deepEqual`](https://github.com/ivan7237d/antiutils/blob/master/src/internal/deepEqual.ts) that recursively delegates to those functions depending on the object type.
 
+## Reducers
+
+The library exports a type `Reducer` which is like a regular reducer, but can return `undefined` to stop the iteration short, and which is used by functions [`reduceIterable`](https://github.com/ivan7237d/antiutils/blob/master/src/internal/iterable/reduceIterable.ts) and [`scanIterable`](https://github.com/ivan7237d/antiutils/blob/master/src/internal/iterable/scanIterable.ts).
+
+The library includes [basic implementations of this type](https://github.com/ivan7237d/antiutils/blob/master/src/internal/reducer), all of which except the boolean ones (`andReducer` and `orReducer`) can also be used with arrays and observables.
+
 ## Lenses
 
 First let's talk about how we define a lens. When building React components, it's convenient to work with a type which we'll call `StateView`, a combination of a value and a setter:

src/internal/reducer/andReducer.test.ts

@@ -0,0 +1,10 @@
+import { applyPipe } from '../applyPipe';
+import { reduceIterable } from '../iterable/reduceIterable';
+import { andReducer } from './andReducer';
+
+it('works', () => {
+  expect(applyPipe([true, true], reduceIterable(andReducer))).toEqual(true);
+  expect(applyPipe([true, false], reduceIterable(andReducer))).toEqual(false);
+  expect(applyPipe([false, true], reduceIterable(andReducer))).toEqual(false);
+  expect(applyPipe([false, false], reduceIterable(andReducer))).toEqual(false);
+});

src/internal/reducer/andReducer.ts

@@ -0,0 +1,2 @@
+export const andReducer = (accumulator: boolean, value: boolean) =>
+  accumulator ? value : undefined;

src/internal/reducer/countReducer.test.ts

@@ -0,0 +1,7 @@
+import { applyPipe } from '../applyPipe';
+import { reduceIterable } from '../iterable/reduceIterable';
+import { countReducer } from './countReducer';
+
+it('works', () => {
+  expect(applyPipe([1, 2], reduceIterable(countReducer))).toEqual(2);
+});

src/internal/reducer/countReducer.ts

@@ -0,0 +1 @@
+export const countReducer = (accumulator: number) => accumulator + 1;

src/internal/reducer/maxReducer.test.ts

@@ -0,0 +1,7 @@
+import { applyPipe } from '../applyPipe';
+import { reduceIterable } from '../iterable/reduceIterable';
+import { maxReducer } from './maxReducer';
+
+it('works', () => {
+  expect(applyPipe([1, 2], reduceIterable(maxReducer))).toEqual(2);
+});

src/internal/reducer/maxReducer.ts

@@ -0,0 +1,2 @@
+export const maxReducer = (accumulator: number, value: number) =>
+  Math.max(accumulator, value);

src/internal/reducer/minReducer.test.ts

@@ -0,0 +1,7 @@
+import { applyPipe } from '../applyPipe';
+import { reduceIterable } from '../iterable/reduceIterable';
+import { minReducer } from './minReducer';
+
+it('works', () => {
+  expect(applyPipe([1, 2], reduceIterable(minReducer))).toEqual(1);
+});

src/internal/reducer/minReducer.ts

@@ -0,0 +1,2 @@
+export const minReducer = (accumulator: number, value: number) =>
+  Math.min(accumulator, value);

src/internal/reducer/orReducer.test.ts

@@ -0,0 +1,10 @@
+import { applyPipe } from '../applyPipe';
+import { reduceIterable } from '../iterable/reduceIterable';
+import { orReducer } from './orReducer';
+
+it('works', () => {
+  expect(applyPipe([true, true], reduceIterable(orReducer))).toEqual(true);
+  expect(applyPipe([true, false], reduceIterable(orReducer))).toEqual(true);
+  expect(applyPipe([false, true], reduceIterable(orReducer))).toEqual(true);
+  expect(applyPipe([false, false], reduceIterable(orReducer))).toEqual(false);
+});

src/internal/reducer/orReducer.ts

@@ -0,0 +1,2 @@
+export const orReducer = (accumulator: boolean, value: boolean) =>
+  accumulator ? undefined : value;

src/internal/reducer/sumReducer.test.ts

@@ -0,0 +1,7 @@
+import { applyPipe } from '../applyPipe';
+import { reduceIterable } from '../iterable/reduceIterable';
+import { sumReducer } from './sumReducer';
+
+it('works', () => {
+  expect(applyPipe([1, 2], reduceIterable(sumReducer))).toEqual(3);
+});

src/internal/reducer/sumReducer.ts

@@ -0,0 +1,2 @@
+export const sumReducer = (accumulator: number, value: number) =>
+  accumulator + value;