Uncurry
My last post had me thinking of some of the ways the function uncurry is useful in Haskell. Let’s first look at the type:
uncurry :: (a -> b -> c) -> (a, b) -> cUsually the results are obvious, transforming a given function by simply taking a couple of its arguments and replacing them with a single tuple argument. But sometimes we can get something a bit more interesting:
uncurry (flip (,)) :: (a, b) -> (b, a)— swap tuple elements around.uncurry (flip (,)) ("hello", "world") ==> ("world", "hello")uncurry ($) :: (a -> b, a) -> b— function application within a tuple; second element applied to the first.uncurry ($) ((+3), 4) ==> 7uncurry const :: (a, b) -> a— oops! we’ve un-optimized ourselves back to the equivalent offst.uncurry (flip const) :: (a, b) -> b— and we can duplicatesndby adding a flip.map . uncurry :: (a -> b -> c) -> [(a, b)] -> [c]— apply function over a list, getting arguments from within tuples in that list.(map . uncurry) (+) [(1,1), (2,3), (5,10)] ==> [2,5,15]
So basically, uncurry is a heavy-duty higher-order tool for working with tuples.
