newbie2009 wrote:
I am a newbie. Consider this code:
square x = x * x add3 x y z = x + y + z add x y = x + y composition5 x = (square . add3) x composition6 x y = (square . add3) x y
1) What arguments can i pass to composition5? Please give an example of calling it. 2) What arguments can i pass to composition6? Please give an example of calling it. 3) How can I write the function "add" to take any number of arguments? I would like to call it either as "add 1 2" or "add 1 2 3" etc
Thank you.
for (1) and (2) you can ask haskell what the types are, Prelude> :t composition5 composition5 :: (Num (a -> a -> a), Num a) => a -> a -> a -> a Prelude> :t composition6 composition6 :: (Num (a -> a -> a), Num a) => a -> a -> a -> a This is a worry, it wants binary operation to be a number but it is not! There must be an error in the program. Let us try and fix by changing them to composition5 x = (square . add x) composition6 x y = (square . add3 x y) y now we see: Prelude> :t composition5 composition5 :: (Num a) => a -> a -> a Prelude> :t composition6 composition6 :: (Num a) => a -> a -> a which is reasonable, Prelude> composition5 1 2 9 Prelude> composition6 3 4 121 As for question 3, one would be better to take a list of numbers and to add [1,2,3] instead of add 1 2 3. (Something similar to add 1 2 3 is possible in a couple different way (have a go without using any typeclasses!) but more advanced than one should like to bother with at this point). add [] = 0 add (x:xs) = x + add xs would be fine anyway. -- View this message in context: http://old.nabble.com/Function-composition-questions-from-a-newbie-tp2657020... Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.