Document comma-separated conditions in language FAQ

[lucaswerkmeister]

The Language design Frequently Asked Questions¹ should cover our syntax of comma-separated conditions

if (exists a, nonempty b)

since newcomers will naturally want to write

if (exists a && nonempty b)

This could be added to the existing section Prefix form for is Type, exists, and nonempty (with a generalized title), or a new section below it. I vote for the former – I think that

• the prefix form of these conditions,
• the need for comma-separating them (ambiguity of exists x = a && b), and
• the existence of and difference to their postfix forms, which do not need commas

should better be explained in a single section.

I can take a stab at this tomorrow.

¹ which, aside, would look much better as Language Design Frequently Asked Questions

[lucaswerkmeister]

That section needs an update in general. This “confusing unsupported syntax”

if (!person is Employee) { ... } //confusing unsupported syntax

is actually supported. And of course it talks about how the postfix form doesn’t work when in fact it is available.

[ePaul]

@lucaswerkmeister While if(! person is Employee){ ... } is valid syntax, it doesn't narrow down the type of person (what the whole point of conditions vs. expressions is). Maybe this is what was meant with the comment?