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T.P.Readers.LaTeX.Parsing: Monoid and Semigroup instances for TokStream.

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John MacFarlane 2022-03-12 10:23:25 -08:00
parent 6abcde0bf7
commit f9a4e049c5
1 changed files with 8 additions and 0 deletions
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src/Text/Pandoc/Readers/LaTeX/Parsing.hs
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@ -251,6 +251,14 @@ instance Default LaTeXState where
data TokStream = TokStream !Bool [Tok]
deriving (Show)
instance Semigroup TokStream where
(TokStream exp1 ts1) <> (TokStream exp2 ts2) =
TokStream (if null ts1 then exp2 else exp1) (ts1 <> ts2)
instance Monoid TokStream where
mempty = TokStream False mempty
mappend = (<>)
instance Monad m => Stream TokStream m Tok where
uncons (TokStream _ []) = return Nothing
uncons (TokStream _ (t:ts)) = return $ Just (t, TokStream False ts)