Haskell apply single value to a list of functions
haskell
Solution
You can use the `$` operator, which stands for function application.
> map ($ 3) [(+3), (*4), (+1)]
[6,12,4]
This basically expands to `[(+3) $ 3, (*4) $ 3, (+1) $ 3]`, which is just function application.
Problem
For an assignment I am working on a list of functions `[Int -> Int]` (eg. `[(+3), (*4), (+1)]` ) and I would like to apply a single `Int` to each of them, in turn creating a list of results `[Int]` I already searched a lot, but I am unable to find a way to do such an operation. Using `map` does not work as I would expect. The related error is this: ``` ERROR - Cannot infer instance *** Instance : Num ((Label -> Label) -> a) ``` As requested the code: ``` data Tree = Node (Label -> Label) Label [Tree] type Label = Int testTree = Node (+1) 3 [ Node (+1) 5 [], Node (+1) 4 [Node (+1) 1 [], Node (+2) 7 []]] listify :: Tree -> [(Label -> Label)] listify t = [(getNodeFunction t)] ++ concat(map (listify) (getSubTrees t)) *Main> map (\f -> f 7) (listify testTree) ``` this actually works. Had a piece of faulty code in the file still, sorry for the fuss.