src/Tools/Haskell/Library.hs

more formal references;

{- generated by Isabelle -}

{-  Title:      Tools/Haskell/Library.hs
    Author:     Makarius
    LICENSE:    BSD 3-clause (Isabelle)

Basic library of Isabelle idioms.

See also "$ISABELLE_HOME/src/Pure/General/basics.ML", "$ISABELLE_HOME/src/Pure/library.ML".
-}

module Isabelle.Library (
  (|>), (|->), (#>), (#->),

  the, the_default,

  fold, fold_rev, single, map_index, get_index,

  quote, trim_line)
where

import Data.Maybe


{- functions -}

(|>) :: a -> (a -> b) -> b
x |> f = f x

(|->) :: (a, b) -> (a -> b -> c) -> c
(x, y) |-> f = f x y

(#>) :: (a -> b) -> (b -> c) -> a -> c
(f #> g) x = x |> f |> g

(#->) :: (a -> (c, b)) -> (c -> b -> d) -> a -> d
(f #-> g) x  = x |> f |-> g


{- options -}

the :: Maybe a -> a
the (Just x) = x
the Nothing = error "the Nothing"

the_default :: a -> Maybe a -> a
the_default x Nothing = x
the_default _ (Just y) = y


{- lists -}

fold :: (a -> b -> b) -> [a] -> b -> b
fold _ [] y = y
fold f (x : xs) y = fold f xs (f x y)

fold_rev :: (a -> b -> b) -> [a] -> b -> b
fold_rev _ [] y = y
fold_rev f (x : xs) y = f x (fold_rev f xs y)

single :: a -> [a]
single x = [x]

map_index :: ((Int, a) -> b) -> [a] -> [b]
map_index f = map_aux 0
  where
    map_aux _ [] = []
    map_aux i (x : xs) = f (i, x) : map_aux (i + 1) xs

get_index :: (a -> Maybe b) -> [a] -> Maybe (Int, b)
get_index f = get_aux 0
  where
    get_aux _ [] = Nothing
    get_aux i (x : xs) =
      case f x of
        Nothing -> get_aux (i + 1) xs
        Just y -> Just (i, y)


{- strings -}

quote :: String -> String
quote s = "\"" ++ s ++ "\""

trim_line :: String -> String
trim_line line =
  case reverse line of
    '\n' : '\r' : rest -> reverse rest
    '\n' : rest -> reverse rest
    _ -> line