CODEWITHSUNDEEP
functionhaskellpattern-matching
user2999349
user2999349

Reputation: 879

Haskell function patterns 'otherwise'

Is there a way I can create a function with multiple definitions for different patterns including one that is executed when no of the other function's statements patterns are matched?

E.g.:

someFunc (pattern1) = def1
someFunc (pattern2) = def2
someFunc (<otherwise/all other possible values>) = def3

Or if this is not possible, how can it be achieved?

Thanks in advance!

Best regards, Skyfe.

Upvotes: 0

Views: 547

Answers (1)

bheklilr
bheklilr

Reputation: 54058

You can use the wildcard match _:

isJust :: Maybe a -> Bool
-- Here we don't care about what's inside the `Just`
isJust (Just _) = True
-- Here we don't care what it is, it's not a `Just` so return `False`
isJust _ = False

For clarification, patterns are tried in the order you define them, so the above function is not equivalent to

isJust _ = False
isJust (Just _) = True

because the _ pattern is matched first. What the compiler is actually doing is turning this into a case statement internally, so the first function would be equivalent to

isJust x = case x of
    Just _ -> True
    _      -> False

and as we know from every other programming language that has ever existed, case statements are tried in order.

Upvotes: 6

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