[mercury-users] Can this be done better?

Richard O'Keefe ok at cs.otago.ac.nz
Tue Jan 31 12:47:50 AEDT 2012

On 31/01/2012, at 4:09 AM, Michael Richter wrote:
>    main(!IO) :-
>        Forward = [math.sin, math.cos, (func(X) = math.ln(X))],
>        Reverse = [math.asin, math.acos, (func(X) = math.exp(X))],
>        Results = list.map_corresponding(
>           (func(F, R) = compose(R, F, 0.5)), Forward, Reverse),
>        io.write_list(Results, ", ", io.write_float, !IO),
>        io.write_string("\n", !IO).
> THIS is awesome, however!  There's a lot of stuff in the standard library, but the documentation is … a wee bit terse.  I completely overlooked that one.

When I had a similar problem some time back, map_corresponding is what I went
looking for.  I was *expecting* it to be called zipWith (as in Haskell's List
module) or map (as in SML's ListPair module, or Quintus Prolog's 'lists' one).
map2 looked pretty close, but had the wrong modes.

Haskell has a nice feature:  you can look up a function in the core libraries
by giving its type signature.  Visit http://www.haskell.org/hoogle/
and type
	(a -> b -> c) -> [a] -> [b] -> [c]
into the search box.  It should be possible to adapt this to Mercury.

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