This was prompted by the 'minor annoyances thread'. A big annoyance
for me is the recurring `_ {}` at the end of alt patterns that fall
through. A worse form is `_ { fail "this is a bug"; }` (alt already
fails when not matching, with a line number reference to the alt that
blew up, so this kind of `fail` statements mostly just muddle up the
code).
Instead, I propose:
// This one falls through without failing
alt myoption pass {
some(x) { do_something_with(x); }
}
// This one explicitly says that is is non-exhaustive, and that
// it will fail for bad input
alt myoption fail {
some(x) { ... }
}
Normal alt would be required to be exhaustive, and give a compile-time
error if it isn't. This is more self-documenting (you're explicitly
annotating what you're trying to do when writing a non-exhaustive
alt), and somewhat more succinct.
I'm not terribly attached to those keywords (`pass` and `fail`), would
happily hear alternatives.
Best,
Marijn
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