Elvish: Map explosion and rest options

[xiaq]

Use $%m to explode a map, like how you use $@a to explode a list.

~> fn f [&foo=bar &lorem=ipsum]{ echo $foo $lorem }
~> m = [&foo=qux &lorem=dolar]
~> f $%m
qux dolar
~> put [$%m k=v]
[&foo=bar &lorem=ipsum &k=v]

Rest option:

~> fn f [%opts]{ echo $opts }
~> f &foo=bar &lorem=ipsum
[&foo=bar &lorem=ipsum]

[ghost]

why use % and not @ as well to keep consistency?

[xiaq]

You need a different sigil in the lambda parameter list to disambiguate rest argument and rest option.

You also need it to disambiguate between [$@li] and [$%m] since Elvish uses [] for both lists and maps.

[ghost]

But like kind-of $li and kind-of $m should be different so it should be possible for the implementation to do the right thing?

[xiaq]

In lambda signatures @li and %m are declarations, so you cannot know their types.

In other cases, yes it's doable by looking at the type dynamically, but I tend towards having more static information.

[kwshi]

I tentatively suggest a @@ operator, a la Python's * for lists vs ** for maps. It feels more consistent/easy to remember than %, IMO.

[xiaq]

The choice of % is in analogy to Perl's hash sigil.

[zzamboni]

As a former Perl-head, I thoroughly endorse the choice of % 😃