Safe Haskell	Safe
Language	Haskell98

Safe

Contents

New functions
Safe wrappers

Description

A module wrapping Prelude/Data.List functions that can throw exceptions, such as head and !!. Each unsafe function has up to four variants, e.g. with tail:

tail :: [a] -> [a], raises an error on tail [].
tailMay :: [a] -> Maybe [a], turns errors into Nothing.
tailDef :: [a] -> [a] -> [a], takes a default to return on errors.
tailNote :: String -> [a] -> [a], takes an extra argument which supplements the error message.
tailSafe :: [a] -> [a], returns some sensible default if possible, [] in the case of tail.

This module also introduces some new functions, documented at the top of the module.

Synopsis

New functions

abort :: String -> a Source

Synonym for error. Used for instances where the program has decided to exit because of invalid user input, or the user pressed quit etc. This function allows error to be reserved for programmer errors.

at :: [a] -> Int -> a Source

Synonym for !!, but includes more information in the error message.

lookupJust :: Eq a => a -> [(a, b)] -> b Source

lookupJust key = fromJust . lookup key

findJust :: (a -> Bool) -> [a] -> a Source

findJust op = fromJust . find op

elemIndexJust :: Eq a => a -> [a] -> Int Source

elemIndexJust op = fromJust . elemIndex op

findIndexJust :: (a -> Bool) -> [a] -> Int Source

findIndexJust op = fromJust . findIndex op

Safe wrappers

tailMay :: [a] -> Maybe [a] Source

tailMay [] = Nothing
tailMay [1,3,4] = Just [3,4]

tailDef :: [a] -> [a] -> [a] Source

tailDef [12] [] = [12]
tailDef [12] [1,3,4] = [3,4]

tailNote :: String -> [a] -> [a] Source

tailNote "help me" [] = error "Safe.tailNote [], help me"
tailNote "help me" [1,3,4] = [3,4]

tailSafe :: [a] -> [a] Source

tailSafe [] = []
tailSafe [1,3,4] = [3,4]

initMay :: [a] -> Maybe [a] Source

initDef :: [a] -> [a] -> [a] Source

initNote :: String -> [a] -> [a] Source

initSafe :: [a] -> [a] Source

headMay :: [a] -> Maybe a Source

headDef :: a -> [a] -> a Source

headNote :: String -> [a] -> a Source

lastMay :: [a] -> Maybe a Source

lastDef :: a -> [a] -> a Source

lastNote :: String -> [a] -> a Source

minimumMay :: Ord a => [a] -> Maybe a Source

minimumDef :: Ord a => a -> [a] -> a Source

minimumNote :: Ord a => String -> [a] -> a Source

maximumMay :: Ord a => [a] -> Maybe a Source

maximumDef :: Ord a => a -> [a] -> a Source

maximumNote :: Ord a => String -> [a] -> a Source

minimumByMay :: (a -> a -> Ordering) -> [a] -> Maybe a Source

minimumByDef :: a -> (a -> a -> Ordering) -> [a] -> a Source

minimumByNote :: String -> (a -> a -> Ordering) -> [a] -> a Source

maximumByMay :: (a -> a -> Ordering) -> [a] -> Maybe a Source

maximumByDef :: a -> (a -> a -> Ordering) -> [a] -> a Source

maximumByNote :: String -> (a -> a -> Ordering) -> [a] -> a Source

foldr1May :: (a -> a -> a) -> [a] -> Maybe a Source

foldr1Def :: a -> (a -> a -> a) -> [a] -> a Source

foldr1Note :: String -> (a -> a -> a) -> [a] -> a Source

foldl1May :: (a -> a -> a) -> [a] -> Maybe a Source

foldl1Def :: a -> (a -> a -> a) -> [a] -> a Source

foldl1Note :: String -> (a -> a -> a) -> [a] -> a Source

foldl1May' :: (a -> a -> a) -> [a] -> Maybe a Source

foldl1Def' :: a -> (a -> a -> a) -> [a] -> a Source

foldl1Note' :: String -> (a -> a -> a) -> [a] -> a Source

scanl1May :: (a -> a -> a) -> [a] -> Maybe [a] Source

scanl1Def :: [a] -> (a -> a -> a) -> [a] -> [a] Source

scanl1Note :: String -> (a -> a -> a) -> [a] -> [a] Source

scanr1May :: (a -> a -> a) -> [a] -> Maybe [a] Source

scanr1Def :: [a] -> (a -> a -> a) -> [a] -> [a] Source

scanr1Note :: String -> (a -> a -> a) -> [a] -> [a] Source

fromJustDef :: a -> Maybe a -> a Source

An alternative name for fromMaybe, to fit the naming scheme of this package. Generally using fromMaybe directly would be considered better style.

fromJustNote :: String -> Maybe a -> a Source

assertNote :: String -> Bool -> a -> a Source

atMay :: [a] -> Int -> Maybe a Source

atDef :: a -> [a] -> Int -> a Source

atNote :: String -> [a] -> Int -> a Source

readMay :: Read a => String -> Maybe a Source

readDef :: Read a => a -> String -> a Source

readNote :: Read a => String -> String -> a Source

lookupJustDef :: Eq a => b -> a -> [(a, b)] -> b Source

lookupJustNote :: Eq a => String -> a -> [(a, b)] -> b Source

findJustDef :: a -> (a -> Bool) -> [a] -> a Source

findJustNote :: String -> (a -> Bool) -> [a] -> a Source

elemIndexJustDef :: Eq a => Int -> a -> [a] -> Int Source

elemIndexJustNote :: Eq a => String -> a -> [a] -> Int Source

findIndexJustDef :: Int -> (a -> Bool) -> [a] -> Int Source

findIndexJustNote :: String -> (a -> Bool) -> [a] -> Int Source

toEnumMay :: (Enum a, Bounded a) => Int -> Maybe a Source

toEnumDef :: (Enum a, Bounded a) => a -> Int -> a Source

toEnumNote :: (Enum a, Bounded a) => String -> Int -> a Source

toEnumSafe :: (Enum a, Bounded a) => Int -> a Source