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| -rw-r--r-- | Utility/Tense.hs | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/Utility/Tense.hs b/Utility/Tense.hs new file mode 100644 index 000000000..135a90af2 --- /dev/null +++ b/Utility/Tense.hs @@ -0,0 +1,57 @@ +{- Past and present tense text. + - + - Copyright 2012 Joey Hess <joey@kitenet.net> + - + - Licensed under the GNU GPL version 3 or higher. + -} + +{-# LANGUAGE OverloadedStrings #-} + +module Utility.Tense where + +import qualified Data.Text as T +import Data.Text (Text) +import GHC.Exts( IsString(..) ) + +data Tense = Present | Past + deriving (Eq) + +data TenseChunk = Tensed Text Text | UnTensed Text + deriving (Eq, Ord, Show) + +newtype TenseText = TenseText [TenseChunk] + deriving (Eq, Ord) + +{- Allows OverloadedStrings to be used, to build UnTensed chunks. -} +instance IsString TenseChunk where + fromString = UnTensed . T.pack + +{- Allows OverloadedStrings to be used, to provide UnTensed TenseText. -} +instance IsString TenseText where + fromString s = TenseText [fromString s] + +renderTense :: Tense -> TenseText -> Text +renderTense tense (TenseText chunks) = T.concat $ map render chunks + where + render (Tensed present past) + | tense == Present = present + | otherwise = past + render (UnTensed s) = s + +{- Builds up a TenseText, separating chunks with spaces. + - + - However, rather than just intersperse new chunks for the spaces, + - the spaces are appended to the end of the chunks. + -} +tenseWords :: [TenseChunk] -> TenseText +tenseWords = TenseText . go [] + where + go c [] = reverse c + go c (w:[]) = reverse (w:c) + go c ((UnTensed w):ws) = go (UnTensed (addspace w) : c) ws + go c ((Tensed w1 w2):ws) = + go (Tensed (addspace w1) (addspace w2) : c) ws + addspace w = T.append w " " + +unTensed :: Text -> TenseText +unTensed t = TenseText [UnTensed t] |