Compose function with two arguments

Asked Jun 01 '16 at 15:31

Active Jun 01 '16 at 15:31

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I ran into something that threw me off today. I was trying to define a function equivalent to Data.Text.commonPrefixes that throws away everything but the prefix.

The following works:

commonPrefix :: Text -> Text -> Maybe Text
commonPrefix a b = fmap firstTriple $ Text.commonPrefixes a b

firstTriple :: (a, b, c) -> a
firstTriple (a, _, _) = a

I originally tried doing it like this, which doesn't work:

commonPrefix :: Text -> Text -> Maybe Text
commonPrefix = fmap firstTriple . Text.commonPrefixes

Is there a way to define this function as a composition?

asked Jun 01 '16 at 15:31

Sean Clark Hess

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`(fmap firstTriple .) . Text.commonPrefixes` ? – karakfa Jun 01 '16 at 15:45
It looks like `fmap (fmap firstTriple) . Text.commonPrefixes` works too. Thanks everyone! – Sean Clark Hess Jun 01 '16 at 17:28

Compose function with two arguments

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