OCAML function in parameter of another function

Question

I'm trying to pass a function as parameter to another function but I get an error at compilation.

Error: This function has type 'a -> 'a -> int
       It is applied to too many arguments; maybe you forgot a `;'.

My code is:

let sort to_do my_list =
        let rec change to_do my_list verify newlist = match my_list with
                | Empty -> if verify = newlist then newlist else
                           change to_do newlist newlist Empty
                | Item (elem, next) -> change to_do my_list verify (compare to_do elem newlist)
        in
        change to_do my_list my_list Empty
;;

let rec compare to_do elem my_list = match my_list with
        | Empty -> (elem, my_list)
        | Item (elem1, Empty) -> if to_do elem elem1 > 0 then Item (elem, elem1) else
                                  Item (elem1, elem)
        | Item (elem1, next) -> compare to_do elem next
;;

Can you include the definition of the type with Empty and Item variants? — Étienne Millon
– Étienne Millon, Commented Mar 30, 2017 at 9:04

Étienne Millon · Accepted Answer · 2017-03-30 09:06:10Z

2

In sort, you are referring to a function named compare. Since the other function compare is below, that will be resolved to Pervasives.compare : 'a -> 'a -> int (which takes two values and compare them).

Moving your compare function above sort may fix the problem.

answered Mar 30, 2017 at 9:06

Étienne Millon

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Félix Grellard · Accepted Answer · 2017-03-31 09:14:57Z

For the person interesting my final code is :

 let rec comp to_do elem my_list memlist = match my_list with
         | Empty -> Item (elem, memlist)
         | Item (elem1, Empty) -> if to_do elem1 elem > 0 then Item (elem, memlist) else
                                  rev (Item (elem, (rev memlist)))
         | Item (elem1, next) -> comp to_do elem next memlist
 ;;                                                                                                                                                                                           

 let sort to_do my_list =
         let rec change to_do my_list verify newlist = match my_list with
                 | Empty -> if verify = newlist then newlist else
                            change to_do newlist newlist Empty
                 | Item (elem, next) -> change to_do next verify (comp to_do elem newlist newlist)
         in
         change to_do my_list my_list Empty
 ;;

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