ghc-7.10.2: The GHC API

Safe HaskellNone
LanguageHaskell2010

Util

Contents

Description

Highly random utility functions

Synopsis

Flags dependent on the compiler build

General list processing

zipEqual :: String -> [a] -> [b] -> [(a, b)]

zipWithEqual :: String -> (a -> b -> c) -> [a] -> [b] -> [c]

zipWith3Equal :: String -> (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]

zipWith4Equal :: String -> (a -> b -> c -> d -> e) -> [a] -> [b] -> [c] -> [d] -> [e]

zipLazy :: [a] -> [b] -> [(a, b)]

zipLazy is a kind of zip that is lazy in the second list (observe the ~)

stretchZipWith :: (a -> Bool) -> b -> (a -> b -> c) -> [a] -> [b] -> [c]

stretchZipWith p z f xs ys stretches ys by inserting z in the places where p returns True

zipWithAndUnzip :: (a -> b -> (c, d)) -> [a] -> [b] -> ([c], [d])

filterByList :: [Bool] -> [a] -> [a]

filterByList takes a list of Bools and a list of some elements and filters out these elements for which the corresponding value in the list of Bools is False. This function does not check whether the lists have equal length.

unzipWith :: (a -> b -> c) -> [(a, b)] -> [c]

mapFst :: (a -> c) -> [(a, b)] -> [(c, b)]

mapSnd :: (b -> c) -> [(a, b)] -> [(a, c)]

chkAppend :: [a] -> [a] -> [a]

mapAndUnzip :: (a -> (b, c)) -> [a] -> ([b], [c])

mapAndUnzip3 :: (a -> (b, c, d)) -> [a] -> ([b], [c], [d])

mapAccumL2 :: (s1 -> s2 -> a -> (s1, s2, b)) -> s1 -> s2 -> [a] -> (s1, s2, [b])

nOfThem :: Int -> a -> [a]

filterOut :: (a -> Bool) -> [a] -> [a]

Like filter, only it reverses the sense of the test

partitionWith :: (a -> Either b c) -> [a] -> ([b], [c])

Uses a function to determine which of two output lists an input element should join

splitEithers :: [Either a b] -> ([a], [b])

Teases a list of Eithers apart into two lists

dropWhileEndLE :: (a -> Bool) -> [a] -> [a]

foldl1' :: (a -> a -> a) -> [a] -> a Source

A strict version of foldl1

foldl2 :: (acc -> a -> b -> acc) -> acc -> [a] -> [b] -> acc

count :: (a -> Bool) -> [a] -> Int

all2 :: (a -> b -> Bool) -> [a] -> [b] -> Bool

lengthExceeds :: [a] -> Int -> Bool

(lengthExceeds xs n) = (length xs > n)

lengthIs :: [a] -> Int -> Bool

lengthAtLeast :: [a] -> Int -> Bool

atLength :: ([a] -> b) -> (Int -> b) -> [a] -> Int -> b

atLength atLen atEnd ls n unravels list ls to position n. Precisely:

 atLength atLenPred atEndPred ls n
  | n < 0         = atLenPred n
  | length ls < n = atEndPred (n - length ls)
  | otherwise     = atLenPred (drop n ls)

equalLength :: [a] -> [b] -> Bool

compareLength :: [a] -> [b] -> Ordering

leLength :: [a] -> [b] -> Bool

True if length xs <= length ys

isSingleton :: [a] -> Bool

only :: [a] -> a

singleton :: a -> [a]

notNull :: [a] -> Bool

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

isIn :: Eq a => String -> a -> [a] -> Bool

isn'tIn :: Eq a => String -> a -> [a] -> Bool

Tuples

fstOf3 :: (a, b, c) -> a

sndOf3 :: (a, b, c) -> b

thirdOf3 :: (a, b, c) -> c

firstM :: Monad m => (a -> m c) -> (a, b) -> m (c, b)

first3M :: Monad m => (a -> m d) -> (a, b, c) -> m (d, b, c)

third3 :: (c -> d) -> (a, b, c) -> (a, b, d)

uncurry3 :: (a -> b -> c -> d) -> (a, b, c) -> d

List operations controlled by another list

takeList :: [b] -> [a] -> [a]

dropList :: [b] -> [a] -> [a]

splitAtList :: [b] -> [a] -> ([a], [a])

split :: Char -> String -> [String]

dropTail :: Int -> [a] -> [a]

For loop

nTimes :: Int -> (a -> a) -> a -> a

Compose a function with itself n times. (nth rather than twice)

Sorting

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

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

nubSort :: Ord a => [a] -> [a]

Comparisons

eqListBy :: (a -> a -> Bool) -> [a] -> [a] -> Bool

eqMaybeBy :: (a -> a -> Bool) -> Maybe a -> Maybe a -> Bool

thenCmp :: Ordering -> Ordering -> Ordering infixr 9

cmpList :: (a -> a -> Ordering) -> [a] -> [a] -> Ordering

(<&&>) :: Applicative f => f Bool -> f Bool -> f Bool infixr 3

(<||>) :: Applicative f => f Bool -> f Bool -> f Bool infixr 2

Edit distance

fuzzyLookup :: String -> [(String, a)] -> [a]

Search for possible matches to the users input in the given list, returning a small number of ranked results

Transitive closures

transitiveClosure :: (a -> [a]) -> (a -> a -> Bool) -> [a] -> [a]

Strictness

seqList :: [a] -> b -> b

Module names

Argument processing

Floating point

read helpers

maybeRead :: Read a => String -> Maybe a

IO-ish utilities

global :: a -> IORef a

consIORef :: IORef [a] -> a -> IO ()

globalM :: IO a -> IORef a

Filenames and paths

type Suffix = String

data Direction

Constructors

Forwards 
Backwards 

Utils for defining Data instances

mkNoRepType :: String -> DataType Source

Constructs a non-representation for a non-representable type

Utils for printing C code

Hashing

hashString :: String -> Int32

A sample hash function for Strings. We keep multiplying by the golden ratio and adding. The implementation is:

hashString = foldl' f golden
  where f m c = fromIntegral (ord c) * magic + hashInt32 m
        magic = 0xdeadbeef

Where hashInt32 works just as hashInt shown above.

Knuth argues that repeated multiplication by the golden ratio will minimize gaps in the hash space, and thus it's a good choice for combining together multiple keys to form one.

Here we know that individual characters c are often small, and this produces frequent collisions if we use ord c alone. A particular problem are the shorter low ASCII and ISO-8859-1 character strings. We pre-multiply by a magic twiddle factor to obtain a good distribution. In fact, given the following test:

testp :: Int32 -> Int
testp k = (n - ) . length . group . sort . map hs . take n $ ls
  where ls = [] : [c : l | l <- ls, c <- ['\0'..'\xff']]
        hs = foldl' f golden
        f m c = fromIntegral (ord c) * k + hashInt32 m
        n = 100000

We discover that testp magic = 0.