haskell - How to define 'special' behavior for composite function in `.hs` file? -

composition normal in haskell, know can define special behavior of composite function, says

prelude> (floor . sqrt) (10^55) 3162277660168379365112938496 prelude> let (floor . sqrt) n | n < 2 = n | otherwise = head $ dropwhile (\x -> x^2 > n) $ iterate (\x -> (x + n `div` x) `div` 2) (n `div` 2) prelude> (floor . sqrt) (10^55) 3162277660168379331998893544 

the result special define function correct (because of floating point error in first one).

now want same inside .hs file, like

(floor . sqrt) n     | n < 2 = n     | otherwise = head $ dropwhile (\x -> x^2 > n)                        $ iterate (\x -> (x + n `div` x) `div` 2) (n `div` 2)  main =     print $ (floor . sqrt) (10^55) 

this time ghc yelling @ me

ambiguous occurrence `.' refer either `main..', defined @ me.hs:1:8                       or `prelude..',                          imported `prelude' @ me.hs:1:1                          (and defined in `ghc.base') 

so possible define function in .hs file? (define inside main let okey, however).

first of all, example in ghci not defining special composition of floor , sqrt. instead, it's defining operator (.) takes 3 arguments named floor, sqrt, , n , hides existing standard function named (.).

you apply new function standard library functions floor , sqrt, become parameters same names in new (.) function.

the error because top-level definition not automatically hide existing definition, , anyway that's not want do.

now, can define entirely new function (hopefully own name, in groovy's answer) specialized floor . sqrt function, there's no way in haskell define specialized version of existing functions.

what might thinking of, , possible, using compiler pragma rewrite rules in ghc automatically replace specific expressions equivalent, improved versions. should careful rewritten form gives same answer replaces, though. otherwise you're risking baffling debugging sessions.