Question

This is my code:

type HoraAtendimento = (String, Int, Int)  htmlHAtendimento :: [HoraAtendimento] -> Html htmlHAtendimento [] = toHtml '' htmlHAtendimento ((da,hia,hfa):[]) = toHtml da +++ 'feira '                                      +++                                      show hia +++ 'h - ' +++ show hfa +++ 'h' htmlHAtendimento ((da,hia,hfa):r) = toHtml da +++ 'feira '                                     +++                                     show hia +++ 'h - ' +++ show hfa +++ 'h, '                                     +++                                     htmlHAtendimento r 

I’m looking for a way to use the map function and get rid of this recursive function. Is that possible and if so, how do I do it?

Answer 1

Look at the type of map. It is (a -> b) -> [a] -> [b]. That doesn’t look like your type, which is [a] -> b. That’s not a map, that’s a fold.

The higher-order function you want to look at is foldr. See Hoogle.

Something like…

htmlHAtendimento :: [HoraAtendimento] -> Html htmlHAtendimento [] = toHtml '' htmlHAtendimento l = foldr1 (+++) $ intersperse ', ' $ map f l   where f (da, hia, hfa) = toHtml da                            +++ 'feira '                            +++ show hia                            +++ 'h - '                            +++ show hfa                            +++ 'h' 

I don’t know if that’s correct, but that’s in the right direction.