Underscore Variables

[eignnx]

The underscore _ is a valid variable name, but it doesn't mean the same as in prolog:

?- [1, 2] = [_|_].
    true.

-- {1 2} = {_ .._}
    - [false]

It ought to do the prolog thing i.e. spawn a fresh variable each time it's mentioned.

[eignnx]

Also I want [Key._] to be equivalent to [key _] cause that lets you silence singleton variable warnings easily.