lhs2tex-1.21: src/Auxiliaries.lhs
%-------------------------------= --------------------------------------------
\subsection{Auxiliaries}
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%if codeOnly || showModuleHeader
> module Auxiliaries ( module Auxiliaries )
> where
>
> import Data.Char ( isSpace )
> import Control.Arrow ( (>>>), Kleisli(..) )
> import qualified Control.Arrow as A
%endif
> infixr 5 {-"\;"-} <| -- same fixity as `|:|'
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\subsubsection{Operations on chars}
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> unNL :: Char -> Char
> unNL '\n' = ' '
> unNL c = c
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\subsubsection{Operations on lists}
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> splitOn :: (Char -> Bool) -> String -> [String]
> splitOn p s = case dropWhile p s of
> "" -> []
> s' -> w : splitOn p s''
> where (w,s'') = break p s'
> rtake :: Int -> [a] -> [a]
> rtake n = reverse . take n . reverse
> inverse :: [(a, b)] -> [(b, a)]
> inverse bs = [ (b, a) | (a, b) <- bs ]
> merge :: (Ord a) => [a] -> [a] -> [a]
> merge [] bs = bs
> merge as@(_a : _) [] = as
> merge as@(a : as') bs@(b : bs')
> | a <= b = a : merge as' bs
> | otherwise = b : merge as bs'
%{
%format (sub (a) (b)) = "{" a "}_{" b "}"
The call |breakAfter p [sub a 1,..,sub a n]| yields |([sub a 1,..,sub a
i], [sub a (i+1),..,sub a n])| such that |p (sub a i) = True| and |p
(sub a j) = False| for |j < i|.
%}
> breakAfter :: (a -> Bool) -> [a] -> ([a], [a])
> breakAfter _p [] = ([], [])
> breakAfter p (a : as)
> | p a = ([a], as)
> | otherwise = a <| breakAfter p as
> breaks :: ([a] -> Bool) -> [a] -> ([a], [a])
> breaks _p [] = ([], [])
> breaks p as@(a : as')
> | p as = ([], as)
> | otherwise = a <| breaks p as'
> -- isPrefix :: (Eq a) => [a] -> [a] -> Bool
> -- p `isPrefix` as = p == take (length p) as
> withoutSpaces :: String -> String
> withoutSpaces s = filter (not . isSpace) s
> group :: Int -> [a] -> [[a]]
> group n = repSplit (repeat n) >>> takeWhile (not . null)
> repSplit :: [Int] -> [a] -> [[a]]
> repSplit [] _xs = []
> repSplit (n : ns) xs = ys : repSplit ns zs
> where (ys, zs) = splitAt n xs
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\subsubsection{Monad utilities}
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> lift :: (Monad m) => (a -> b) -> (a -> m b)
> lift f a = return (f a)
> (***) :: (Monad m) => (a -> m a') -> (b -> m b') -> (a, b) -> m (a', b')
> f *** g = runKleisli (Kleisli f A.*** Kleisli g)
> fromRight :: Either a b -> b
> fromRight (Left _) = error "fromRight"
> fromRight (Right b) = b
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\subsubsection{Miscellaneous}
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Some useful type abbreviations.
> type LineNo = Int
> type Message = String
> type Exc = (Message, String)
Reverse Composition.
> (<|) :: a -> ([a], b) -> ([a], b)
> a <| (as, b) = (a : as, b)
>
> impossible :: String -> a
> impossible name = error ("The `impossible' happened in \""
> ++ name ++ "\"")