| safe-0.2: Library for safe (pattern match free) functions | Contents | Index |
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Safe | Portability | portable | Stability | in-progress | Maintainer | http://www.cs.york.ac.uk/~ndm/ |
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Description |
A library for safe functions, based on standard functions that may crash.
For more details see http://www-users.cs.york.ac.uk/~ndm/safe/
In general, each unsafe function has up to 4 forms.
Since tail has all the possible forms, it is fully documented.
The others all follow the same pattern.
- Note, takes an extra argument which supplements the error message, tailNote
- Def, take an extra argument to give when a crash would otherwise happen, tailDef
- May, wraps the result in a Maybe, tailMay
- Safe, returns a default type if possible, tailSafe
This library also introduces three brand new functions:
- at - synonym for (!!)
- lookupJust - defined as lookupJust k = fromJust . lookup k
- abort - same as error, but different intended meaning
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Synopsis |
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Documentation |
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tailDef :: [a] -> [a] -> [a] |
tailDef [12] [] = [12]
tailDef [12] [1,3,4] = [3,4]
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tailMay :: [a] -> Maybe [a] |
tailMay [] = Nothing
tailMay [1,3,4] = Just [3,4]
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tailNote :: String -> [a] -> [a] |
tail "help me" [] = error "Pattern match failure, tail [], help me"
tail "help me" [1,3,4] = [3,4]
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tailSafe :: [a] -> [a] |
tailSafe [] = []
tailSafe [1,3,4] = [3,4]
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initDef :: [a] -> [a] -> [a] |
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initMay :: [a] -> Maybe [a] |
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initNote :: String -> [a] -> [a] |
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initSafe :: [a] -> [a] |
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headDef :: a -> [a] -> a |
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headMay :: [a] -> Maybe a |
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headNote :: String -> [a] -> a |
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lastDef :: a -> [a] -> a |
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lastMay :: [a] -> Maybe a |
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lastNote :: String -> [a] -> a |
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minimumDef :: Ord a => a -> [a] -> a |
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minimumMay :: Ord a => [a] -> Maybe a |
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minimumNote :: Ord a => String -> [a] -> a |
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maximumDef :: Ord a => a -> [a] -> a |
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maximumMay :: Ord a => [a] -> Maybe a |
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maximumNote :: Ord a => String -> [a] -> a |
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foldr1Def :: a -> (a -> a -> a) -> [a] -> a |
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foldr1May :: (a -> a -> a) -> [a] -> Maybe a |
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foldr1Note :: String -> (a -> a -> a) -> [a] -> a |
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foldl1Def :: a -> (a -> a -> a) -> [a] -> a |
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foldl1May :: (a -> a -> a) -> [a] -> Maybe a |
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foldl1Note :: String -> (a -> a -> a) -> [a] -> a |
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fromJustDef :: a -> Maybe a -> a |
See fromMaybe
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fromJustNote :: String -> Maybe a -> a |
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assertNote :: String -> Bool -> a -> a |
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at :: [a] -> Int -> a |
Same as (!!), but better error message
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atDef :: a -> [a] -> Int -> a |
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atMay :: [a] -> Int -> Maybe a |
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atNote :: String -> [a] -> Int -> a |
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readDef :: Read a => a -> String -> a |
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readMay :: Read a => String -> Maybe a |
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readNote :: Read a => String -> String -> a |
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lookupJust :: Eq a => a -> [(a, b)] -> b |
lookupJust key = fromJust . lookup key
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lookupJustDef :: Eq a => b -> a -> [(a, b)] -> b |
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lookupJustNote :: Eq a => String -> a -> [(a, b)] -> b |
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abort :: String -> a |
Exactly the same as error. Use this for instances where the program
has decided to exit because of invalid user input, or the user pressed
quit etc. This allows error to be reserved for genuine coding mistakes.
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