57 lines
1.5 KiB
Haskell
57 lines
1.5 KiB
Haskell
{- Past and present tense text.
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-
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- Copyright 2012 Joey Hess <joey@kitenet.net>
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-
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- License: BSD-2-clause
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-}
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{-# LANGUAGE OverloadedStrings #-}
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module Utility.Tense where
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import qualified Data.Text as T
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import Data.Text (Text)
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import GHC.Exts( IsString(..) )
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data Tense = Present | Past
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deriving (Eq)
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data TenseChunk = Tensed Text Text | UnTensed Text
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deriving (Eq, Ord, Show)
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newtype TenseText = TenseText [TenseChunk]
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deriving (Eq, Ord)
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{- Allows OverloadedStrings to be used, to build UnTensed chunks. -}
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instance IsString TenseChunk where
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fromString = UnTensed . T.pack
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{- Allows OverloadedStrings to be used, to provide UnTensed TenseText. -}
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instance IsString TenseText where
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fromString s = TenseText [fromString s]
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renderTense :: Tense -> TenseText -> Text
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renderTense tense (TenseText chunks) = T.concat $ map render chunks
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where
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render (Tensed present past)
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| tense == Present = present
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| otherwise = past
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render (UnTensed s) = s
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{- Builds up a TenseText, separating chunks with spaces.
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-
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- However, rather than just intersperse new chunks for the spaces,
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- the spaces are appended to the end of the chunks.
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-}
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tenseWords :: [TenseChunk] -> TenseText
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tenseWords = TenseText . go []
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where
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go c [] = reverse c
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go c (w:[]) = reverse (w:c)
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go c ((UnTensed w):ws) = go (UnTensed (addspace w) : c) ws
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go c ((Tensed w1 w2):ws) =
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go (Tensed (addspace w1) (addspace w2) : c) ws
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addspace w = T.append w " "
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unTensed :: Text -> TenseText
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unTensed t = TenseText [UnTensed t]
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