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implementation module StdMaybe
// ********************************************************************************
// Clean StdLib library module, version 1.0
// ********************************************************************************
from StdFunc import :: St;
from StdOverloaded import class ==(..);
:: Maybe x
= Just x
| Nothing
isJust :: !(Maybe .x) -> Bool
isJust Nothing = False
isJust _ = True
isNothing :: !(Maybe .x) -> Bool
isNothing Nothing = True
isNothing _ = False
u_isJust :: !u:(Maybe .x) -> (!Bool, !u:Maybe .x)
u_isJust nothing=:Nothing
= (False, nothing)
u_isJust just
= (True, just)
u_isNothing :: !u:(Maybe .x) -> (!Bool, !u:Maybe .x)
u_isNothing nothing=:Nothing
= (True, nothing)
u_isNothing just
= (False,just)
fromJust :: !(Maybe .x) -> .x
fromJust (Just x) = x
accMaybe :: .(St .x .a) !u:(Maybe .x) -> (!Maybe .a,!u:Maybe .x)
accMaybe f (Just x)
# (a,x) = f x
= (Just a,Just x)
accMaybe _ nothing
= (Nothing,nothing)
mapMaybe :: .(.x -> .y) !(Maybe .x) -> Maybe .y
mapMaybe f (Just x) = Just (f x)
mapMaybe _ nothing = Nothing
instance == (Maybe x) | == x where
(==) Nothing maybe = case maybe of
Nothing -> True
just -> False
(==) (Just a) maybe = case maybe of
Just b -> a==b
nothing -> False
maybeToList :: !(Maybe .a) -> [.a];
maybeToList Nothing = []
maybeToList (Just a) = [a]
listToMaybe :: ![.a] -> .Maybe .a;
listToMaybe [] = Nothing
listToMaybe [a:_] = Just a
catMaybes :: ![Maybe .a] -> .[.a];
catMaybes ms = [ m \\ Just m <- ms ]
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