Haskell Language Lists Filtering with `filter`
Example
Given a list:
li = [1,2,3,4,5]
we can filter a list with a predicate using filter :: (a -> Bool) -> [a] -> [a]:
filter (== 1) li -- [1]
filter (even) li -- [2,4]
filter (odd) li -- [1,3,5]
-- Something slightly more complicated
comfy i = notTooLarge && isEven
where
notTooLarge = (i + 1) < 5
isEven = even i
filter comfy li -- [2]
Of course it's not just about numbers:
data Gender = Male | Female deriving Show
data Person = Person String Gender Int deriving Show
onlyLadies :: [Person] -> Person
onlyLadies x = filter isFemale x
where
isFemale (Person _ Female _) = True
isFemale _ = False
onlyLadies [(Person "Alex" Male 31),(Person "Ellie" Female 29)]
-- [Person "Ellie" Female 29]
