Add Tuple support: _1, _2

CHANGELOG.md

@@ -13,6 +13,13 @@
 **Note**: Gaps between patch versions are faulty/broken releases. **Note**: A feature tagged as Experimental is in a
 high state of flux, you're at risk of it changing without notice.
 
+# 2.4.0
+
+- **New Feature**
+  - `Tuple`
+    - add `_1` constructor (@toastal)
+    - add `_2` constructor (@toastal)
+
 # 2.3.11
 
 - **Bug Fix**

package.json

@@ -1,6 +1,6 @@
 {
   "name": "monocle-ts",
-  "version": "2.3.11",
+  "version": "2.4.0",
   "description": "A porting of scala monocle library to TypeScript",
   "main": "lib/index.js",
   "module": "es6/index.js",

src/Tuple.ts

@@ -0,0 +1,24 @@
+/**
+ * @since 2.4.0
+ */
+import { fst, snd, map, mapLeft } from 'fp-ts/lib/Tuple'
+import { constant } from 'fp-ts/lib/function'
+import { Lens } from '.'
+
+// TODO on fp-ts upgrade: map → mapFst
+const one = new Lens<[any, any], any>(fst, (x) => map(constant(x)))
+
+/**
+ * @category constructor
+ * @since 2.4.0
+ */
+export const _1 = <A, B>(): Lens<[A, B], A> => one
+
+// TODO on fp-ts upgrade: mapLeft → mapSnd
+const two = new Lens<[any, any], any>(snd, (y) => mapLeft(constant(y)))
+
+/**
+ * @category constructor
+ * @since 2.4.0
+ */
+export const _2 = <A, B>(): Lens<[A, B], B> => two

test/Tuple.ts

@@ -0,0 +1,17 @@
+import * as assert from 'assert'
+import { _1, _2 } from '../src/Tuple'
+import * as U from './util'
+
+describe('Tuple', () => {
+  const mock: [number, string] = [1, 'a']
+
+  it('gets', () => {
+    assert.strictEqual(_1().get(mock), 1)
+    assert.strictEqual(_2().get(mock), 'a')
+  })
+
+  it('sets', () => {
+    U.deepStrictEqual(_1().set(2)(mock), [2, 'a'])
+    U.deepStrictEqual(_2().set('b')(mock), [1, 'b'])
+  })
+})