New Feature: add Char, closes #12

README.md

@@ -76,13 +76,15 @@ For the `Prism` type, see the [monocle-ts](https://github.com/gcanti/monocle-ts)
 
 ## Builtin refinements
 
+- `Char`
 - `Integer`
 - `Negative`
 - `NegativeInteger`
 - `NonNegative`
 - `NonNegativeInteger`
 - `NonPositive`
 - `NonPositiveInteger`
+- `NonEmptyString`
 - `NonZero`
 - `NonZeroInteger`
 - `Positive`

src/Char.ts

@@ -0,0 +1,9 @@
+import { Prism } from 'monocle-ts'
+import { Newtype, prism, URIOf } from './'
+import { NonEmptyString } from './NonEmptyString'
+
+export interface Char extends Newtype<URIOf<NonEmptyString> & { readonly Length: 1 }, string> {}
+
+export const isChar = (s: string) => s.length === 1
+
+export const prismChar: Prism<string, Char> = prism<Char>(isChar)

test/Char.ts

@@ -0,0 +1,11 @@
+import * as assert from 'assert'
+import { none, some } from 'fp-ts/lib/Option'
+import { prismChar } from '../src/Char'
+
+describe('Char', () => {
+  it('prismChar', () => {
+    assert.deepEqual(prismChar.getOption('a'), some('a'))
+    assert.deepEqual(prismChar.getOption('ab'), none)
+    assert.deepEqual(prismChar.getOption(''), none)
+  })
+})

test/NontEmptyString.ts

@@ -5,6 +5,7 @@ import { prismNonEmptyString } from '../src/NonEmptyString'
 describe('NonEmptyString', () => {
   it('prismNonEmptyString', () => {
     assert.deepEqual(prismNonEmptyString.getOption('a'), some('a'))
+    assert.deepEqual(prismNonEmptyString.getOption('ab'), some('ab'))
     assert.deepEqual(prismNonEmptyString.getOption(''), none)
   })
 })