CODEWITHSUNDEEP
listhaskell
user2879704
user2879704

Reputation:

Pass multiple arguments to map's func argument

In python, with list comprehension, i can pass multiple arguments to a map function's function argument as,

  const = 2 
  def divide(x,y):
    return x/y
  [divide(x, const) for x in [2,4,6,8]]

How can i do the same in haskell using map function?

Something like this,

func x y = x/y

map (func x 2) [2 4 6 8]

I think, it can be done using function currying, but not sure about the correct way?

Upvotes: 3

Views: 2515

Answers (1)

Random Dev
Random Dev

Reputation: 52280

using sections

you can use a section like this:

Prelude> let func x y = x / y
Prelude> map (`func` 2) [2,4,6,8]
[1.0,2.0,3.0,4.0]

see when you write a function in backticks you make it into an operator - then you can plug in values to the left or to the right to (for x or y here).

If you wanted to substitute for x then you could have used normal partial application as well:

Prelude> map (func 24) [2,4,6,8]
[12.0,6.0,4.0,3.0]

which is the same as

Prelude> map (24 `func`) [2,4,6,8]
[12.0,6.0,4.0,3.0]

using a lambda

of course if you don't like this at all you can always use lambda's:

Prelude> map (\x -> func x 2) [2,4,6,8]
[1.0,2.0,3.0,4.0]

using list-comprehension

or you can do the same as you did in Python (use a list comprehension):

Prelude> [ func x 2 | x <- [2,4,6,8] ]
[1.0,2.0,3.0,4.0]

ok I think right now I can think of no other (easy) ones ;)

using partial application with flip

flip and partial application (I think a bit less readable - but I find it kind of funny ;):

Prelude> map (flip f 2) [2,4,6,8]
[1.0,2.0,3.0,4.0]

remark / div

as you only dealt with Ints here you probably would want to use div instead of (/):

Prelude> map (`div` 2) [2,4,6,8]
[1,2,3,4]

Upvotes: 8

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