Safe Haskell | Ignore |
---|---|
Language | GHC2021 |
GHC.Utils.Misc
Contents
- Miscellaneous higher-order functions
- General list processing
- Tuples
- List operations controlled by another list
- Sorting
- Comparisons
- Edit distance
- Transitive closures
- Strictness
- Module names
- Integers
- Floating point
- IO-ish utilities
- Filenames and paths
- Utils for defining Data instances
- Utils for printing C code
- Hashing
- Call stacks
Description
Highly random utility functions
Synopsis
- applyWhen :: Bool -> (a -> a) -> a -> a
- nTimes :: Int -> (a -> a) -> a -> a
- const2 :: a -> b -> c -> a
- zipEqual :: HasDebugCallStack => String -> [a] -> [b] -> [(a, b)]
- zipWithEqual :: HasDebugCallStack => String -> (a -> b -> c) -> [a] -> [b] -> [c]
- zipWith3Equal :: HasDebugCallStack => String -> (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]
- zipWith4Equal :: HasDebugCallStack => String -> (a -> b -> c -> d -> e) -> [a] -> [b] -> [c] -> [d] -> [e]
- stretchZipWith :: (a -> Bool) -> b -> (a -> b -> c) -> [a] -> [b] -> [c]
- zipWithAndUnzip :: (a -> b -> (c, d)) -> [a] -> [b] -> ([c], [d])
- zipAndUnzip :: [a] -> [b] -> ([a], [b])
- filterByList :: [Bool] -> [a] -> [a]
- filterByLists :: [Bool] -> [a] -> [a] -> [a]
- partitionByList :: [Bool] -> [a] -> ([a], [a])
- unzipWith :: (a -> b -> c) -> [(a, b)] -> [c]
- mapFst :: Functor f => (a -> c) -> f (a, b) -> f (c, b)
- mapSnd :: Functor f => (b -> c) -> f (a, b) -> f (a, c)
- chkAppend :: [a] -> [a] -> [a]
- mapAndUnzip :: (a -> (b, c)) -> [a] -> ([b], [c])
- mapAndUnzip3 :: (a -> (b, c, d)) -> [a] -> ([b], [c], [d])
- mapAndUnzip4 :: (a -> (b, c, d, e)) -> [a] -> ([b], [c], [d], [e])
- filterOut :: (a -> Bool) -> [a] -> [a]
- partitionWith :: (a -> Either b c) -> [a] -> ([b], [c])
- partitionWithM :: Monad m => (a -> m (Either b c)) -> [a] -> m ([b], [c])
- dropWhileEndLE :: (a -> Bool) -> [a] -> [a]
- spanEnd :: (a -> Bool) -> [a] -> ([a], [a])
- last2 :: [a] -> Maybe (a, a)
- lastMaybe :: [a] -> Maybe a
- onJust :: b -> Maybe a -> (a -> b) -> b
- foldl1' :: HasCallStack => (a -> a -> a) -> [a] -> a
- foldl2 :: (acc -> a -> b -> acc) -> acc -> [a] -> [b] -> acc
- count :: (a -> Bool) -> [a] -> Int
- countWhile :: (a -> Bool) -> [a] -> Int
- all2 :: (a -> b -> Bool) -> [a] -> [b] -> Bool
- lengthExceeds :: [a] -> Int -> Bool
- lengthIs :: [a] -> Int -> Bool
- lengthIsNot :: [a] -> Int -> Bool
- lengthAtLeast :: [a] -> Int -> Bool
- lengthAtMost :: [a] -> Int -> Bool
- lengthLessThan :: [a] -> Int -> Bool
- listLengthCmp :: [a] -> Int -> Ordering
- atLength :: ([a] -> b) -> b -> [a] -> Int -> b
- equalLength :: [a] -> [b] -> Bool
- compareLength :: [a] -> [b] -> Ordering
- leLength :: [a] -> [b] -> Bool
- ltLength :: [a] -> [b] -> Bool
- isSingleton :: [a] -> Bool
- only :: [a] -> a
- expectOnly :: HasCallStack => String -> [a] -> a
- singleton :: a -> [a]
- notNull :: Foldable f => f a -> Bool
- expectNonEmpty :: HasCallStack => String -> [a] -> NonEmpty a
- snocView :: [a] -> Maybe ([a], a)
- holes :: [a] -> [(a, [a])]
- changeLast :: [a] -> a -> [a]
- whenNonEmpty :: Applicative m => [a] -> (NonEmpty a -> m ()) -> m ()
- mergeListsBy :: (a -> a -> Ordering) -> [[a]] -> [a]
- isSortedBy :: (a -> a -> Ordering) -> [a] -> Bool
- mapMaybe' :: Foldable f => (a -> Maybe b) -> f a -> [b]
- fstOf3 :: (a, b, c) -> a
- sndOf3 :: (a, b, c) -> b
- thdOf3 :: (a, b, c) -> c
- fstOf4 :: (a, b, c, d) -> a
- sndOf4 :: (a, b, c, d) -> b
- fst3 :: (a -> d) -> (a, b, c) -> (d, b, c)
- snd3 :: (b -> d) -> (a, b, c) -> (a, d, 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]
- capitalise :: String -> String
- sortWith :: Ord b => (a -> b) -> [a] -> [a]
- minWith :: Ord b => (a -> b) -> [a] -> a
- nubSort :: Ord a => [a] -> [a]
- ordNub :: Ord a => [a] -> [a]
- ordNubOn :: Ord b => (a -> b) -> [a] -> [a]
- isEqual :: Ordering -> Bool
- 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
- strictMap :: (a -> b) -> [a] -> [b]
- strictZipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
- strictZipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]
- looksLikeModuleName :: String -> Bool
- looksLikePackageName :: String -> Bool
- exactLog2 :: Integer -> Maybe Integer
- readRational :: String -> Rational
- readSignificandExponentPair :: String -> (Integer, Integer)
- readHexRational :: String -> Rational
- readHexSignificandExponentPair :: String -> (Integer, Integer)
- doesDirNameExist :: FilePath -> IO Bool
- getModificationUTCTime :: FilePath -> IO UTCTime
- modificationTimeIfExists :: FilePath -> IO (Maybe UTCTime)
- fileHashIfExists :: FilePath -> IO (Maybe Fingerprint)
- withAtomicRename :: MonadIO m => FilePath -> (FilePath -> m a) -> m a
- type Suffix = String
- splitLongestPrefix :: String -> (Char -> Bool) -> (String, String)
- escapeSpaces :: String -> String
- data Direction
- reslash :: Direction -> FilePath -> FilePath
- makeRelativeTo :: FilePath -> FilePath -> FilePath
- abstractConstr :: String -> Constr
- abstractDataType :: String -> DataType
- mkNoRepType :: String -> DataType
- charToC :: Word8 -> String
- hashString :: String -> Int32
- type HasCallStack = ?callStack :: CallStack
- type HasDebugCallStack = ()
Miscellaneous higher-order functions
General list processing
zipEqual :: HasDebugCallStack => String -> [a] -> [b] -> [(a, b)] #
zipWithEqual :: HasDebugCallStack => String -> (a -> b -> c) -> [a] -> [b] -> [c] #
zipWith3Equal :: HasDebugCallStack => String -> (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d] #
zipWith4Equal :: HasDebugCallStack => String -> (a -> b -> c -> d -> e) -> [a] -> [b] -> [c] -> [d] -> [e] #
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]) #
zipAndUnzip :: [a] -> [b] -> ([a], [b]) #
This has the effect of making the two lists have equal length by dropping the tail of the longer one.
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.
filterByLists :: [Bool] -> [a] -> [a] -> [a] #
filterByLists
takes a list of Bools and two lists as input, and
outputs a new list consisting of elements from the last two input lists. For
each Bool in the list, if it is True
, then it takes an element from the
former list. If it is False
, it takes an element from the latter list.
The elements taken correspond to the index of the Bool in its list.
For example:
filterByLists [True, False, True, False] "abcd" "wxyz" = "axcz"
This function does not check whether the lists have equal length.
partitionByList :: [Bool] -> [a] -> ([a], [a]) #
partitionByList
takes a list of Bools and a list of some elements and
partitions the list according to the list of Bools. Elements corresponding
to True
go to the left; elements corresponding to False
go to the right.
For example, partitionByList [True, False, True] [1,2,3] == ([1,3], [2])
This function does not check whether the lists have equal
length; when one list runs out, the function stops.
mapAndUnzip :: (a -> (b, c)) -> [a] -> ([b], [c]) #
mapAndUnzip3 :: (a -> (b, c, d)) -> [a] -> ([b], [c], [d]) #
mapAndUnzip4 :: (a -> (b, c, d, e)) -> [a] -> ([b], [c], [d], [e]) #
partitionWith :: (a -> Either b c) -> [a] -> ([b], [c]) #
Uses a function to determine which of two output lists an input element should join
partitionWithM :: Monad m => (a -> m (Either b c)) -> [a] -> m ([b], [c]) #
Monadic version of partitionWith
dropWhileEndLE :: (a -> Bool) -> [a] -> [a] #
spanEnd :: (a -> Bool) -> [a] -> ([a], [a]) #
spanEnd p l == reverse (span p (reverse l))
. The first list
returns actually comes after the second list (when you look at the
input list).
onJust :: b -> Maybe a -> (a -> b) -> b #
onJust x m f
applies f to the value inside the Just or returns the default.
foldl1' :: HasCallStack => (a -> a -> a) -> [a] -> a #
A strict version of foldl1
.
countWhile :: (a -> Bool) -> [a] -> Int #
lengthExceeds :: [a] -> Int -> Bool #
(lengthExceeds xs n) = (length xs > n)
lengthIsNot :: [a] -> Int -> Bool #
(lengthIsNot xs n) = (length xs /= n)
lengthAtLeast :: [a] -> Int -> Bool #
(lengthAtLeast xs n) = (length xs >= n)
lengthAtMost :: [a] -> Int -> Bool #
(lengthAtMost xs n) = (length xs <= n)
lengthLessThan :: [a] -> Int -> Bool #
(lengthLessThan xs n) == (length xs < n)
listLengthCmp :: [a] -> Int -> Ordering #
atLength :: ([a] -> b) -> b -> [a] -> Int -> b #
atLength atLen atEnd ls n
unravels list ls
to position n
. Precisely:
atLength atLenPred atEndPred ls n | n < 0 = atLenPred ls | length ls < n = atEndPred (n - length ls) | otherwise = atLenPred (drop n ls)
equalLength :: [a] -> [b] -> Bool #
True if length xs == length ys
compareLength :: [a] -> [b] -> Ordering #
isSingleton :: [a] -> Bool #
Utility function to go from a singleton list to it's element.
Wether or not the argument is a singleton list is only checked in debug builds.
expectOnly :: HasCallStack => String -> [a] -> a #
Extract the single element of a list and panic with the given message if
there are more elements or the list was empty.
Like expectJust
, but for lists.
expectNonEmpty :: HasCallStack => String -> [a] -> NonEmpty a #
Like expectJust msg . nonEmpty
; a better alternative to fromList
.
snocView :: [a] -> Maybe ([a], a) #
Split a list into its last element and the initial part of the list.
snocView xs = Just (init xs, last xs)
for non-empty lists.
snocView xs = Nothing
otherwise.
Unless both parts of the result are guaranteed to be used
prefer separate calls to last
+ init
.
If you are guaranteed to use both, this will
be more efficient.
Compute all the ways of removing a single element from a list.
holes [1,2,3] = [(1, [2,3]), (2, [1,3]), (3, [1,2])]
changeLast :: [a] -> a -> [a] #
Replace the last element of a list with another element.
whenNonEmpty :: Applicative m => [a] -> (NonEmpty a -> m ()) -> m () #
mergeListsBy :: (a -> a -> Ordering) -> [[a]] -> [a] #
Merge an unsorted list of sorted lists, for example:
mergeListsBy compare [ [2,5,15], [1,10,100] ] = [1,2,5,10,15,100]
\( O(n \log{} k) \)
isSortedBy :: (a -> a -> Ordering) -> [a] -> Bool #
Tuples
List operations controlled by another list
splitAtList :: [b] -> [a] -> ([a], [a]) #
Given two lists xs and ys, return `splitAt (length xs) ys`.
capitalise :: String -> String #
Convert a word to title case by capitalising the first letter
Sorting
sortWith :: Ord b => (a -> b) -> [a] -> [a] #
The sortWith
function sorts a list of elements using the
user supplied function to project something out of each element
In general if the user supplied function is expensive to compute then
you should probably be using sortOn
, as it only needs
to compute it once for each element. sortWith
, on the other hand
must compute the mapping function for every comparison that it performs.
ordNubOn :: Ord b => (a -> b) -> [a] -> [a] #
Remove duplicates but keep elements in order. O(n * log n)
Comparisons
removeSpaces :: String -> String #
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
strictZipWith :: (a -> b -> c) -> [a] -> [b] -> [c] #
strictZipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d] #
Module names
looksLikeModuleName :: String -> Bool #
looksLikePackageName :: String -> Bool #
Integers
Floating point
readRational :: String -> Rational #
readSignificandExponentPair :: String -> (Integer, Integer) #
Parse a string into a significand and exponent. A trivial example might be: ghci> readSignificandExponentPair "1E2" (1,2) In a more complex case we might return a exponent different than that which the user wrote. This is needed in order to use a Integer significand. ghci> readSignificandExponentPair "-1.11E5" (-111,3)
readHexRational :: String -> Rational #
readHexSignificandExponentPair :: String -> (Integer, Integer) #
Parse a string into a significand and exponent according to the "Hexadecimal Floats in Haskell" proposal. A trivial example might be: ghci> readHexSignificandExponentPair "0x1p+1" (1,1) Behaves similar to readSignificandExponentPair but the base is 16 and numbers are given in hexadecimal: ghci> readHexSignificandExponentPair "0xAp-4" (10,-4) ghci> readHexSignificandExponentPair "0x1.2p3" (18,-1)
IO-ish utilities
doesDirNameExist :: FilePath -> IO Bool #
getModificationUTCTime :: FilePath -> IO UTCTime #
fileHashIfExists :: FilePath -> IO (Maybe Fingerprint) #
withAtomicRename :: MonadIO m => FilePath -> (FilePath -> m a) -> m a #
Filenames and paths
escapeSpaces :: String -> String #
makeRelativeTo :: FilePath -> FilePath -> FilePath #
Utils for defining Data instances
abstractConstr :: String -> Constr #
abstractDataType :: String -> DataType #
mkNoRepType :: String -> DataType #
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.
Call stacks
type HasCallStack = ?callStack :: CallStack #
Request a CallStack.
NOTE: The implicit parameter ?callStack :: CallStack
is an
implementation detail and should not be considered part of the
CallStack
API, we may decide to change the implementation in the
future.
@since base-4.9.0.0
type HasDebugCallStack = () #
A call stack constraint, but only when isDebugOn
.