[Swift-devel] Call function.

[Mihael Hategan]

On Fri, 2011-08-12 at 16:39 +0000, Ben Clifford wrote:
> What would be needed to write 'map' in swift(script) for use as a library 
> function by other swift code? (rather than writing it in karajan or java)
> 
> It might look something like this: (standby for bleeding eyes on the first 
> line)
> 
> (X out[]) map( (X)f(Y), Y inp[]) {
>   foreach v,i in inp {
>     out[i] = f(v);  // or equivalently out[i] = f( inp[i] );
>   }
> }
> 
> The above adds syntax for passing a function f which takes a value of type 
> Y and returns a value of type X. f is invoked by juxtaposition rather than 
> by an explicit call, though I think that is irrelevant for this message.
> 
> But for map to work for arbitrary 1-d arrays, X and Y need to be type 
> variables of some kind, not actual concrete types.
> 
> We haven't discussed that at all in this thread, but I think it would be 
> needed to do the above kind of thing. That's nothing particularly fancy 
> though its another shift away from fortran-era types - C++ templates, java 
> generics can both express this in some form, as can haskell.
> 
> Comments?
> 

True, but we can still cover a lot of cases with:

type mrfile;
type kv {
  string key;
  mrfile value;
}

(kv[] intermediate) map_((kv[] r) proc(string key, mrfile value), kv[]
input) {
   ...
}

(mrfile[string][] out2) collect_(kv[] intermediate) {
  ...
}

(mrfile[] result) reduce_((mrfile[]) proc(mrfile[string]),
mrfile[string][]) {
  ...
}

I agree though. A full treatment of the issue would require type
parameters.

Mihael