Add decamelize function

Text/Inflections.hs

@@ -1,12 +1,17 @@
 module Text.Inflections
     ( dasherize
-    , transliterate
-    , transliterateCustom
+
+    , decamelize
+    , decamelizeCustom
 
     , defaultMap
 
     , parameterize
-    , parameterizeCustom )
+    , parameterizeCustom
+
+    , transliterate
+    , transliterateCustom
+    )
 where
 
 import Data.Char (isAscii)
@@ -18,6 +23,9 @@ import Text.Inflections.Parameterize ( Transliterations
                                      , parameterize
                                      , parameterizeCustom )
 
+import Text.Inflections.Decamelize ( decamelize
+                                    , decamelizeCustom )
+
 -- |Replaces underscores with dashes in the string.
 dasherize :: String -> String
 dasherize = map (\c -> if c == ' ' then '-' else c)

Text/Inflections/Decamelize.hs

@@ -0,0 +1,20 @@
+module Text.Inflections.Decamelize (decamelize, decamelizeCustom) where
+
+import Text.Inflections.Parse.CamelCase (Word(..), parser)
+import Text.Parsec (ParseError, parse)
+import Data.Char (toLower)
+import Data.List (intercalate)
+
+decamelize :: String -> Either ParseError String
+decamelize s = decamelizeCustom [] s
+
+decamelizeCustom :: [String] -> String -> Either ParseError String
+decamelizeCustom acronyms s =
+  case parse (parser acronyms) "(unknown)" s of
+    Left errs -> Left errs
+    Right res -> Right $ intercalate "_" $ map toDowncasedString res
+
+toDowncasedString :: Word -> String
+toDowncasedString w = map toLower $ wordToS w
+  where wordToS (Word s)    = s
+        wordToS (Acronym s) = s

inflections.cabal

@@ -24,6 +24,7 @@ library
                        , Text.Inflections.Parse.Parameterizable
   other-modules:         Text.Inflections.Data
                        , Text.Inflections.Parameterize
+                       , Text.Inflections.Decamelize
   ghc-options:         -Wall
   build-depends:       base >=4.5 && <4.7, parsec, containers
   default-language:    Haskell2010

test/Text/Inflections/Parse/CamelCaseTest.hs

@@ -28,8 +28,8 @@ tests = [testGroup "parsing"
         ]
 
 fromRight :: Either a b -> b
-fromRight (Left _)  = error
-                      "Either.Unwrap.fromRight: Argument takes form 'Left _'"
+fromRight (Left _)  =
+    error "Either.Unwrap.fromRight: Argument takes form 'Left _'"
 fromRight (Right x) = x
 
 test_lowerCamelCase = fromRight (parse (parser []) "" "testThis") @?=