CODEWITHSUNDEEP
sml
user1756555
user1756555

Reputation: 31

Anonymous function in ml

I've to write a anonymous function that take a list of integer and two functions f and g.The function apply f on the even int in the list and apply g on the odd int. finally the function return the sum of all computed values..f(x)=2x,g(x)=x*x

my code is

val f = fn x => 2 * x;
val g = fn x => x * x;

fun s [] f g = []
 | s L f g =
   let 
     val n = hd(L) mod 2;
   in
    fn n => case n of
   0 => f(hd(L)) + s tl(L) f g
 | x => g(hd(L)) + s tl(L) f g
   end;

what is wrong??

Upvotes: 3

Views: 1077

Answers (1)

pad
pad

Reputation: 41290

First, you should put parentheses around tl(L) so the invoke of s (tl(L)) f g is parsed correctly. Second, the return type of the function is int so the base case [] should return 0 and the inductive case shouldn't have fn n => (because n is already defined by val).

I refactored the function using pattern matching instead of hd, tl and put the frequent changing argument as the last one:

fun sum f g [] = 0
 | sum f g (x::xs) =
   let 
     val n = x mod 2
   in
     case n of
       0 => f x + sum f g xs
     | _ => g x + sum f g xs
   end;

Upvotes: 2

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