Hello, I am wondering how to map functions in sml or Metalanguage. I would like

Question

Hello, I am wondering how to map functions in sml or Metalanguage. I would like to apply the concatanation function toevery element like this

map (op :: )      (which doesn't work)

I was thinking I could do something like this...

fun xa (a, b)= a::b;

fun mm(a) = map xa;

but I get a wierd error
- mm [[1,2,3], [8, 9 , 10], [23]];
stdIn:54.1-54.32 Warning: type vars not generalized because of
   value restriction are instantiated to dummy types(X1,X2,...)
val it = fn : (?.X1 * ?.X1 list) list -> ?.X1 list list
- mm ([1,2,3], [8, 9 , 10], [23]);
stdIn:55.1-55.32 Warning: type vars not generalized because of
   value restriction are instantiated to dummy types(X1,X2,...)
val it = fn : (?.X1 * ?.X1 list) list -> ?.X1 list list

Any ideas about how to go about doing this?

Thanks in advance for any input.

Explanation / Answer

//Hope this will helpyou.

- fun map f = fn[] => []  | (x::xs) => f x ::map f xs; val map = fn : ('a -> 'b) -> 'a list -> 'b list - f([1,2,3]); val it = [2,3] : int list - - fun map f = fn[] => []  | (x::xs) => f x ::map f xs; val map = fn : ('a -> 'b) -> 'a list -> 'b list - f([1,2,3]); val it = [2,3] : int list -

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