Mapping an element to a list of functions in Haskell-CodePudding

The Prelude function map in Haskell applies a function to a list of inputs:

map :: (a -> b) -> [a] -> [b]

If we would like to apply an element to a list of functions, we could do this with recursion:

functionMap :: a -> [a -> b] -> [b]
functionMap element functions = case functions of
  []   -> []
  x:xs -> x element : functionMap element xs

How could we simplify the above recursion with higher order functions, such as foldl, foldr or map, if it is possible?

CodePudding user response：

You can map over the functions and apply each to element:

functionMap :: a -> [a -> b] -> [b]
functionMap element functions = map (\f -> f element) functions

This can be shortened using the $ operator to:

functionMap :: a -> [a -> b] -> [b]
functionMap element functions = map ($ element) functions

or just:

functionMap :: a -> [a -> b] -> [b]
functionMap element = map ($ element)

(also: functionMap = map . flip id)