Add stripSuffix

Author: hdgarrood

docs/Data/String.md

@@ -89,6 +89,17 @@ string left after removing it, as a Just value. Otherwise, return Nothing.
 * `stripPrefix "http:" "http://purescript.org" == Just "//purescript.org"`
 * `stripPrefix "http:" "https://purescript.org" == Nothing`
 
+#### `stripSuffix`
+
+``` purescript
+stripSuffix :: String -> String -> Maybe String
+```
+
+If the string ends with the given suffix, return the portion of the
+string left after removing it, as a Just value. Otherwise, return Nothing.
+* `stripSuffix ".exe" "psc.exe" == Just "psc"`
+* `stripSuffix ".exe" "psc" == Nothing`
+
 #### `fromCharArray`
 
 ``` purescript
@@ -198,8 +209,9 @@ of the string for which the predicate holds.
 split :: String -> String -> Array String
 ```
 
-Returns the substrings of the first string separated along occurences
-of the second string.
+Returns the substrings of the second string separated along occurences
+of the first string.
+* `split " " "hello world" == ["hello", "world"]`
 
 #### `toCharArray`
 

src/Data/String.purs

@@ -24,6 +24,7 @@ module Data.String
   , drop
   , dropWhile
   , stripPrefix
+  , stripSuffix
   , split
   , toCharArray
   , toLower
@@ -105,6 +106,18 @@ stripPrefix prefix str =
     Just 0 -> Just $ drop (length prefix) str
     _      -> Nothing
 
+-- | If the string ends with the given suffix, return the portion of the
+-- | string left after removing it, as a Just value. Otherwise, return Nothing.
+-- | * `stripSuffix ".exe" "psc.exe" == Just "psc"`
+-- | * `stripSuffix ".exe" "psc" == Nothing`
+stripSuffix :: String -> String -> Maybe String
+stripSuffix suffix str =
+  case lastIndexOf suffix str of
+    Just x | x == length str - length suffix ->
+      Just $ take x str
+    _ ->
+      Nothing
+
 -- | Converts an array of characters into a string.
 foreign import fromCharArray :: Array Char -> String