From 7c25859b53db6cdfa0d00afa2501977aa8cb5515 Mon Sep 17 00:00:00 2001
From: gcanti <giulio.canti@gmail.com>
Date: Wed, 5 Jun 2019 17:34:26 +0200
Subject: [PATCH] add isNonEmpty

---
 docs/modules/Array.ts.md | 15 ++++++++++++++-
 src/Array.ts             | 13 +++++++++++--
 test/Array.ts            |  8 +++++++-
 3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/docs/modules/Array.ts.md b/docs/modules/Array.ts.md
index 9f3c26490..6e6fb1e15 100644
--- a/docs/modules/Array.ts.md
+++ b/docs/modules/Array.ts.md
@@ -45,6 +45,7 @@ Adapted from https://github.com/purescript/purescript-arrays
 - [insertAt (function)](#insertat-function)
 - [intersection (function)](#intersection-function)
 - [isEmpty (function)](#isempty-function)
+- [isNonEmpty (function)](#isnonempty-function)
 - [isOutOfBound (function)](#isoutofbound-function)
 - [last (function)](#last-function)
 - [lefts (function)](#lefts-function)
@@ -138,7 +139,7 @@ value and the rest of the array.
 **Signature**
 
 ```ts
-export function chop<A, B>(f: (as: Array<A>) => [B, Array<A>]): (as: Array<A>) => Array<B> { ... }
+export function chop<A, B>(f: (as: NonEmptyArray<A>) => [B, Array<A>]): (as: Array<A>) => Array<B> { ... }
 ```
 
 **Example**
@@ -790,6 +791,18 @@ assert.strictEqual(isEmpty([]), true)
 
 Added in v2.0.0
 
+# isNonEmpty (function)
+
+Test whether an array is non empty narrowing down the type to `NonEmptyArray<A>`
+
+**Signature**
+
+```ts
+export function isNonEmpty<A>(as: Array<A>): as is NonEmptyArray<A> { ... }
+```
+
+Added in v2.0.0
+
 # isOutOfBound (function)
 
 Test whether an array contains a particular index
diff --git a/src/Array.ts b/src/Array.ts
index 52d72e941..a7707a692 100644
--- a/src/Array.ts
+++ b/src/Array.ts
@@ -301,6 +301,15 @@ export function isEmpty<A>(as: Array<A>): boolean {
   return as.length === 0
 }
 
+/**
+ * Test whether an array is non empty narrowing down the type to `NonEmptyArray<A>`
+ *
+ * @since 2.0.0
+ */
+export function isNonEmpty<A>(as: Array<A>): as is NonEmptyArray<A> {
+  return as.length > 0
+}
+
 /**
  * Test whether an array contains a particular index
  *
@@ -1113,11 +1122,11 @@ export function sortBy<A>(ords: Array<Ord<A>>): (as: Array<A>) => Array<A> {
  *
  * @since 2.0.0
  */
-export function chop<A, B>(f: (as: Array<A>) => [B, Array<A>]): (as: Array<A>) => Array<B> {
+export function chop<A, B>(f: (as: NonEmptyArray<A>) => [B, Array<A>]): (as: Array<A>) => Array<B> {
   return as => {
     const result: Array<B> = []
     let cs: Array<A> = as
-    while (cs.length > 0) {
+    while (isNonEmpty(cs)) {
       const [b, c] = f(cs)
       result.push(b)
       cs = c
diff --git a/test/Array.ts b/test/Array.ts
index 93f065d65..739bff51f 100644
--- a/test/Array.ts
+++ b/test/Array.ts
@@ -56,7 +56,8 @@ import {
   findLastMap,
   getShow,
   reverse,
-  getEq
+  getEq,
+  isNonEmpty
 } from '../src/Array'
 import { left, right } from '../src/Either'
 import { fold as foldMonoid, monoidSum, monoidString } from '../src/Monoid'
@@ -152,6 +153,11 @@ describe('Array', () => {
     assert.strictEqual(isEmpty([]), true)
   })
 
+  it('isNotEmpty', () => {
+    assert.strictEqual(isNonEmpty(as), true)
+    assert.strictEqual(isNonEmpty([]), false)
+  })
+
   it('cons', () => {
     assert.deepStrictEqual(cons(0, as), [0, 1, 2, 3])
     assert.deepStrictEqual(cons([1], [[2]]), [[1], [2]])