Map list of functions on list in Haskell

Question

I have a problem with implementing FP (Backus) interpreter in Haskell. FP functions look like this: ``` [+,*]:<2,3> ``` should result with ``` <+:<2,3>, *:<2,3>> -> <5,6> ``` meaning that every function from list on left side should be performed on every every element of a list on a right side. What I understand is that I need something similar to "map" function, but map applies one function on a list, and I need list of functions on a list of values. Thank you in advance! :-) EDIT: Since I wasn't precise, here is my code that doesn't work: ``` apply :: [String] -> [Integer] -> [Integer] apply fs v = [((apply_f f x) | f <- fs | x <- v)] apply_f :: String -> [Integer] -> [Integer] apply_f "+" v = [(sum v)] apply_f "*" v = [(product v)] ``` I can't figure out why... :-( EDIT 2: Sorry, I was too tired from working all day on this. Problem is that I don't need second pipe, just first one: ``` apply fs v = [ apply_f f v | f <- fs ] ``` Now, everything works just fine, thank you very much!…

Accepted Answer

Do you want something like this?

```
[f x | f <- [(+3),(*2)], x <- [1..2]]
```

Output:

```
[4,5,2,4]
```

EDIT:

So something like this?

```
[[f x | f <- [(+3),(*2)]] | x <- [1..2]]
[[4,2],[5,4]]
```

Map list of functions on list in Haskell

Solution

Problem