haskelloperatorsdot-operator

Dot-operator in haskell

I have a function, that uses the Dot-operator. Now I want to write it without the dot. How can I do this?

all p = and . map p

Is this right?

all p = and (map p)

I get these errors:

4.hs:8:13:
    Couldn't match expected type `[Bool]'
                with actual type `[a0] -> [b0]'
    In the return type of a call of `map'
    Probable cause: `map' is applied to too few arguments
    In the first argument of `and', namely `(map p)'
    In the expression: and (map p)
Solution

  • Look at the definition of (.):

    f . g  =  \ x -> f (g x)

    Expanding this gives

    and . (map p)  =  \x -> and ((map p) x)

    or

    all p x  =  and (map p x)