Add prisms for working with prefixed and suffixed text

CHANGELOG.markdown

@@ -5,6 +5,8 @@
 * Allow building with GHC 9.2.
 * Define `_CharTyLit` in `Language.Haskell.TH.Lens` when building with
   `template-haskell-2.18` or later.
+* Add prisms for working with text with prefixes or suffices in
+  `Data.Text.Strict.Lens` and `Data.Text.Lazy.Lens`
 
 5.0.1 [2021.02.24]
 ------------------

src/Data/Text/Lazy/Lens.hs

@@ -1,6 +1,7 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE RankNTypes #-}
 #if __GLASGOW_HASKELL__ >= 710
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE ViewPatterns #-}
@@ -17,6 +18,7 @@
 ----------------------------------------------------------------------------
 module Data.Text.Lazy.Lens
   ( packed, unpacked
+  , prefixed, suffixed
   , _Text
   , text
   , builder
@@ -82,6 +84,34 @@ unpacked :: Iso' Text String
 unpacked = iso Text.unpack Text.pack
 {-# INLINE unpacked #-}
 
+-- | A 'Prism' stripping a prefix from a text when used as a 'Traversal', or
+-- prepending that prefix when run backwards:
+--
+-- >>> "preview" ^? prefixed "pre"
+-- Just "view"
+--
+-- >>> "review" ^? prefixed "pre"
+-- Nothing
+--
+-- >>> prefixed "pre" # "amble"
+-- "preamble"
+prefixed :: Text -> Prism' Text Text
+prefixed p = prism' (p <>) (Text.stripPrefix p)
+
+-- | A 'Prism' stripping a suffix from a text when used as a 'Traversal', or
+-- appending that suffix when run backwards:
+--
+-- >>> "review" ^? suffixed "view"
+-- Just "re"
+--
+-- >>> "review" ^? suffixed "tire"
+-- Nothing
+--
+-- >>> suffixed ".o" # "hello"
+-- "hello.o"
+suffixed :: Text -> Prism' Text Text
+suffixed q = prism' (<> q) (Text.stripSuffix q)
+
 -- | This is an alias for 'unpacked' that makes it clearer how to use it with @('#')@.
 --
 -- @

src/Data/Text/Strict/Lens.hs

@@ -1,5 +1,6 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE RankNTypes #-}
 #if __GLASGOW_HASKELL__ >= 710
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE ViewPatterns #-}
@@ -16,6 +17,7 @@
 ----------------------------------------------------------------------------
 module Data.Text.Strict.Lens
   ( packed, unpacked
+  , prefixed, suffixed
   , builder
   , text
   , utf8
@@ -84,6 +86,34 @@ unpacked :: Iso' Text String
 unpacked = iso Strict.unpack Strict.pack
 {-# INLINE unpacked #-}
 
+-- | A 'Prism' stripping a prefix from a text when used as a 'Traversal', or
+-- prepending that prefix when run backwards:
+--
+-- >>> "preview" ^? prefixed "pre"
+-- Just "view"
+--
+-- >>> "review" ^? prefixed "pre"
+-- Nothing
+--
+-- >>> prefixed "pre" # "amble"
+-- "preamble"
+prefixed :: Text -> Prism' Text Text
+prefixed p = prism' (p <>) (Strict.stripPrefix p)
+
+-- | A 'Prism' stripping a suffix from a text when used as a 'Traversal', or
+-- appending that suffix when run backwards:
+--
+-- >>> "review" ^? suffixed "view"
+-- Just "re"
+--
+-- >>> "review" ^? suffixed "tire"
+-- Nothing
+--
+-- >>> suffixed ".o" # "hello"
+-- "hello.o"
+suffixed :: Text -> Prism' Text Text
+suffixed q = prism' (<> q) (Strict.stripSuffix q)
+
 -- | This is an alias for 'unpacked' that makes it more obvious how to use it with '#'
 --
 -- >> _Text # "hello" -- :: Text

tests/properties.hs

@@ -32,7 +32,7 @@ import Test.QuickCheck
 import Test.Framework
 import Test.Framework.Providers.QuickCheck2
 import Data.Char (isAlphaNum, isAscii, toUpper)
-import Data.Text.Strict.Lens
+import qualified Data.Text.Strict.Lens as Text
 import Data.List.Lens
 import GHC.Exts (Constraint)
 import Numeric (showHex, showOct, showSigned)
@@ -86,7 +86,7 @@ prop__Just                           = isPrism (_Just :: Prism' (Maybe Int) Int)
 prop_prefixed s                      = isPrism (prefixed s :: Prism' String String)
 
 -- Data.Text.Lens
-prop_text s                          = s^.packed.from packed == s
+prop_text s                          = s^.Text.packed.from Text.packed == s
 --prop_text                           = isIso packed
 
 -- Numeric.Lens