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{- 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]
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