ghc-7.10.2: The GHC API

Safe Haskell | None
Language | Haskell2010

Util

Contents

- Flags dependent on the compiler build
- General list processing
- Tuples
- List operations controlled by another list
- For loop
- Sorting
- Comparisons
- Edit distance
- Transitive closures
- Strictness
- Module names
- Argument processing
- Floating point
- read helpers
- IO-ish utilities
- Filenames and paths
- Utils for defining Data instances
- Utils for printing C code
- Hashing

Description

Highly random utility functions

Synopsis

- ghciSupported :: Bool
- debugIsOn :: Bool
- ncgDebugIsOn :: Bool
- ghciTablesNextToCode :: Bool
- isWindowsHost :: Bool
- isDarwinHost :: Bool
- 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)]
- stretchZipWith :: (a -> Bool) -> b -> (a -> b -> c) -> [a] -> [b] -> [c]
- zipWithAndUnzip :: (a -> b -> (c, d)) -> [a] -> [b] -> ([c], [d])
- filterByList :: [Bool] -> [a] -> [a]
- 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]
- partitionWith :: (a -> Either b c) -> [a] -> ([b], [c])
- splitEithers :: [Either a b] -> ([a], [b])
- dropWhileEndLE :: (a -> Bool) -> [a] -> [a]
- foldl1' :: (a -> a -> a) -> [a] -> a
- 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
- lengthIs :: [a] -> Int -> Bool
- lengthAtLeast :: [a] -> Int -> Bool
- listLengthCmp :: [a] -> Int -> Ordering
- atLength :: ([a] -> b) -> (Int -> b) -> [a] -> Int -> b
- equalLength :: [a] -> [b] -> Bool
- compareLength :: [a] -> [b] -> Ordering
- leLength :: [a] -> [b] -> Bool
- 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
- 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
- takeList :: [b] -> [a] -> [a]
- dropList :: [b] -> [a] -> [a]
- splitAtList :: [b] -> [a] -> ([a], [a])
- split :: Char -> String -> [String]
- dropTail :: Int -> [a] -> [a]
- nTimes :: Int -> (a -> a) -> a -> a
- sortWith :: Ord b => (a -> b) -> [a] -> [a]
- minWith :: Ord b => (a -> b) -> [a] -> a
- nubSort :: Ord a => [a] -> [a]
- isEqual :: Ordering -> Bool
- eqListBy :: (a -> a -> Bool) -> [a] -> [a] -> Bool
- eqMaybeBy :: (a -> a -> Bool) -> Maybe a -> Maybe a -> Bool
- thenCmp :: Ordering -> Ordering -> Ordering
- cmpList :: (a -> a -> Ordering) -> [a] -> [a] -> Ordering
- removeSpaces :: String -> String
- (<&&>) :: Applicative f => f Bool -> f Bool -> f Bool
- (<||>) :: Applicative f => f Bool -> f Bool -> f Bool
- fuzzyMatch :: String -> [String] -> [String]
- fuzzyLookup :: String -> [(String, a)] -> [a]
- transitiveClosure :: (a -> [a]) -> (a -> a -> Bool) -> [a] -> [a]
- seqList :: [a] -> b -> b
- looksLikeModuleName :: String -> Bool
- getCmd :: String -> Either String (String, String)
- toCmdArgs :: String -> Either String (String, [String])
- toArgs :: String -> Either String [String]
- readRational :: String -> Rational
- maybeRead :: Read a => String -> Maybe a
- maybeReadFuzzy :: Read a => String -> Maybe a
- doesDirNameExist :: FilePath -> IO Bool
- getModificationUTCTime :: FilePath -> IO UTCTime
- modificationTimeIfExists :: FilePath -> IO (Maybe UTCTime)
- global :: a -> IORef a
- consIORef :: IORef [a] -> a -> IO ()
- globalM :: IO a -> IORef a
- type Suffix = String
- splitLongestPrefix :: String -> (Char -> Bool) -> (String, String)
- escapeSpaces :: String -> String
- data Direction
  - = Forwards
  - | Backwards
- reslash :: Direction -> FilePath -> FilePath
- makeRelativeTo :: FilePath -> FilePath -> FilePath
- abstractConstr :: String -> Constr
- abstractDataType :: String -> DataType
- mkNoRepType :: String -> DataType
- charToC :: Word8 -> String
- hashString :: String -> Int32

# Flags dependent on the compiler build

ghciSupported :: Bool

debugIsOn :: Bool

ncgDebugIsOn :: Bool

ghciTablesNextToCode :: Bool

isWindowsHost :: Bool

isDarwinHost :: Bool

# 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 `Either`s 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

listLengthCmp :: [a] -> Int -> Ordering

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

isEqual :: Ordering -> Bool

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

removeSpaces :: String -> String

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

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

# Edit distance

fuzzyMatch :: String -> [String] -> [String]

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

looksLikeModuleName :: String -> Bool

# Argument processing

getCmd :: String -> Either String (String, String)

toCmdArgs :: String -> Either String (String, [String])

toArgs :: String -> Either String [String]

# Floating point

readRational :: String -> Rational

# read helpers

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

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

# IO-ish utilities

doesDirNameExist :: FilePath -> IO Bool

getModificationUTCTime :: FilePath -> IO UTCTime

modificationTimeIfExists :: FilePath -> IO (Maybe UTCTime)

global :: a -> IORef a

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

globalM :: IO a -> IORef a

# Filenames and paths

type Suffix = String

splitLongestPrefix :: String -> (Char -> Bool) -> (String, String)

escapeSpaces :: String -> String

data Direction

Constructors

Forwards |
Backwards |

reslash :: Direction -> FilePath -> FilePath

makeRelativeTo :: FilePath -> FilePath -> FilePath

# Utils for defining Data instances

abstractConstr :: String -> Constr

abstractDataType :: String -> DataType

mkNoRepType :: String -> DataType Source

Constructs a non-representation for a non-representable type

# Utils for printing C code

charToC :: Word8 -> String

# 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.