Haskell :: Recursion for List of Tuples -


i mapping tuple , managed make work single tuple (a, a). when i've changed tuple [[(a, a)]], says "couldn't match expected type of [(a, a)] (a, a).

    maptuple :: (a -> b) -> [[(a, a)]] -> [(b, b)]     maptuple f [] = []     maptuple f ((a1, a2) : xs) = (f a1, f a2) : maptuple f xs      myfunc :: int -> int     myfunc xk = xk + 1       mytup = [[(1,2),(5,6),(9,10)]] :: [[(int, int)]]     test = maptuple myfunc mytup

couldn't break error yet. missing here. in advance help.

of course maptuple won't work when change type [[(a,a)]] because ((a1, a2) : xs) still has type [(a,a)].

if want apply maptuple list of lists of tuples rather list of tuples don't need change maptuple @ all.

let's @ types second: maptuple (before changed it) had type (a -> b) -> [(a,a)] -> [(b,b)]

partially applying maptuple myfunc [(a,a)] -> [(b,b)]

from comments want function takes [[(1,1),(2,2)],[(3,3)]] :: [[(a,a)]] , returns [[(2,2),(3,3)],[(4,4)]] :: [[(b,b)]]

so want take partial function , apply every [(a,a)] in [[(a,a)]] [[(b,b)]].

so overall want function type: ([(a,a)] -> [(b,b)]) -> [[(a,a)]] -> [[(b,b)]]

this can simplify (a -> b) -> [a] -> [b]. there function us! regular old map.

so using old maptuple type (a -> b) -> [(a, a)] -> [(b, b)] correct result following:

test = map (maptuple myfunc) mytup

hopefully makes sense, if not feel free ask clarification :)


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