[m-users.] if/then/else griping.

[Mark Brown]

Hi,

On Mon, Jul 22, 2019 at 4:16 PM Julian Fondren <jfondren at minimaltype.com> wrote:
>    % Mercury stdlib seems to have settled on this style.
>    % the initial 'if' looks unbalanced vs. the rest of the code.
>    daytype(D) = R :-
>        ( if D = wednesday then
>            R = "humpday"
>        else if (D = sunday; D = saturday) then
>            R = "weekend"
>        else
>            R = "workday"
>        ).

It's the parentheses that are vertically aligned, which I personally
prefer as it is the matching parenthesis that my editor highlights,
not the keyword.

> Maybe this is untrue, but my assumption for a while was that
> if/then/else was added to Mercury in the first place because people
> learning Mercury complained about formatting problems with the
> Prolog-style conditionals. This is odd as the new syntax retains any
> problem you'd have with the old syntax,

If one of your assumptions seems odd, perhaps that is telling you something? :-)

The semantics of Mercury's if-then-else is the same as NU-Prolog's
if-then-else (as opposed to the form written with "->" and ";"), which
is why I think the "if-then-else" spelling is preferred.

Mark