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So I have been using F# for a while and studying a bit of Haskell on the side and I have realized I could rewrite the exact same function one of three different ways.

Either with implicit currying, explicit currying, or with lambda expressions.

//lambdas
let add'  =  fun x -> fun y -> x + y

//explicit currying
let add' x  =     
   let subFunction y = 
      x + y                    
   subFunction   

//implicit currying
let add' x y = x + y

All of these have the signature int -> int -> int. All of them do the same thing.

Which one should I use in which case?

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2  
The one that is most readable and shortest. –  svick Mar 2 at 13:36

1 Answer 1

up vote 5 down vote accepted

In the situations similar to the one you've described you should always use the third option, or, better yet, just let add' = (+) (but beware of Monomorhism Restriction). I see no sense in the other two definitions you have provided.

However, it's common to use nested functions in a way similar to your second example if the nested function takes auxiliary arguments, such as an accumulator in tail-recursive functions.

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Yes I was aware of the (+) option, but I did not list it because it was only applicable when converting an infix operator to a function. –  Alexander Ryan Baggett Mar 2 at 10:08
4  
I would disagree. Compare this: sum xs = fold (+) xs and this: sum = fold (+). In the second case, you have a (partially applied) function on the right hand side, so it is similar to the let add = (+). –  M-x Mar 2 at 10:16

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