Add startsWith and endsWith

Author: triallax

src/Data/String/CodeUnits.js

@@ -116,3 +116,15 @@ exports.splitAt = function (i) {
     return { before: s.substring(0, i), after: s.substring(i) };
   };
 };
+
+exports.startsWith = function (pattern) {
+  return function (s) {
+    return s.startsWith(pattern);
+  }
+}
+
+exports.endsWith = function (pattern) {
+  return function (s) {
+    return s.endsWith(pattern);
+  }
+}

src/Data/String/CodeUnits.purs

@@ -22,6 +22,8 @@ module Data.String.CodeUnits
   , dropWhile
   , slice
   , splitAt
+  , startsWith
+  , endsWith
   ) where
 
 import Prelude
@@ -343,3 +345,19 @@ foreign import _slice :: Int -> Int -> String -> String
 -- | splitAt i s == {before: take i s, after: drop i s}
 -- | ```
 foreign import splitAt :: Int -> String -> { before :: String, after :: String }
+
+-- | Checks whether the given string starts with the pattern.
+-- |
+-- | ```purescript
+-- | startsWith (Pattern "foo") "foobar" == true
+-- | startsWith (Pattern "bar") "foobar" == false
+-- | ```
+foreign import startsWith :: Pattern -> String -> Boolean
+
+-- | Checks whether the given string ends with the pattern.
+-- |
+-- | ```purescript
+-- | endsWith (Pattern "bar") "foobar" == true
+-- | endsWith (Pattern "foo") "foobar" == false
+-- | ```
+foreign import endsWith :: Pattern -> String -> Boolean

test/Test/Data/String/CodeUnits.purs

@@ -510,3 +510,17 @@ testStringCodeUnits = do
     { actual: SCU.slice 3 1000 "purescript"
     , expected: Nothing -- e > l
     }
+
+  log "startsWith"
+  assert $ SCU.startsWith (Pattern "foo") "foobar"
+  assert $ SCU.startsWith (Pattern "foo") "foo"
+  assert $ SCU.startsWith (Pattern "") ""
+  assert $ SCU.startsWith (Pattern "") "foo"
+  assert $ not $ SCU.startsWith (Pattern "foo") ""
+
+  log "endsWith"
+  assert $ SCU.endsWith (Pattern "bar") "foobar"
+  assert $ SCU.endsWith (Pattern "bar") "bar"
+  assert $ SCU.endsWith (Pattern "") ""
+  assert $ SCU.endsWith (Pattern "") "bar"
+  assert $ not $ SCU.endsWith (Pattern "bar") ""