BasePrelude

This module reexports most of the definitions from the "base" package, which are meant to be imported unqualified.

For details check out the source.

Reimplementations of functions presented in versions of "base" newer than 4.6

Data.Bool

bool :: a -> a -> Bool -> a

Case analysis for the Bool type. bool a b p evaluates to a when p is False, and evaluates to b when p is True.

Data.Function

(&) :: a -> (a -> b) -> b infixl 1

& is a reverse application operator. This provides notational convenience. Its precedence is one higher than that of the forward application operator $, which allows & to be nested in $.

Data.Functor

($>) :: Functor f => f a -> b -> f b infixl 4

Flipped version of <$.

Data.List

isSubsequenceOf :: Eq a => [a] -> [a] -> Bool

The isSubsequenceOf function takes two lists and returns True if the first list is a subsequence of the second list.

isSubsequenceOf x y is equivalent to elem x (subsequences y).

Examples

>>> isSubsequenceOf "GHC" "The Glorious Haskell Compiler"
True
>>> isSubsequenceOf ['a','d'..'z'] ['a'..'z']
True
>>> isSubsequenceOf [1..10] [10,9..0]
False

sortOn :: Ord b => (a -> b) -> [a] -> [a]

Sort a list by comparing the results of a key function applied to each element. sortOn f is equivalent to sortBy . comparing f, but has the performance advantage of only evaluating f once for each element in the input list. This is called the decorate-sort-undecorate paradigm, or Schwartzian transform.

uncons :: [a] -> Maybe (a, [a])

Decompose a list into its head and tail. If the list is empty, returns Nothing. If the list is non-empty, returns Just (x, xs), where x is the head of the list and xs its tail.

Debug.Trace

traceShowId :: Show a => a -> a

Like traceShow but returns the shown value instead of a third value.

traceM :: Monad m => String -> m ()

Like trace but returning unit in an arbitrary monad. Allows for convenient use in do-notation. Note that the application of trace is not an action in the monad, as traceIO is in the IO monad.

... = do
  x <- ...
  traceM $ "x: " ++ show x
  y <- ...
  traceM $ "y: " ++ show y

traceShowM :: (Show a, Monad m) => a -> m ()

Like traceM, but uses show on the argument to convert it to a String.

... = do
  x <- ...
  traceShowM $ x
  y <- ...
  traceShowM $ x + y