How to include braces only when "more than one"

[asmaloney]

I have something like the following:

Foo  *foo   `parser:"( @@ "`
FooList []*foo `parser:"| '{' @@+ '}')"`

This works, but it's a bit messy to handle the Foo and FooList cases later on - I would prefer to just work with a FooList.

Is there a way to allow "one foo without braces BUT require braces if there is more than one"?

I tried what seems to be the obvious:

FooList []*foo `parser:"@@ | '{' @@+ '}'"`

but that doesn't work. I assume because @@ won't map to a slice.

[alecthomas]

That construct definitely does work, so there must be some other issue. It could be ambiguity in your grammar. Try putting the '{' case first so there's no lookahead required.

[alecthomas]

But without an error or way to reproduce I can't be sure.

[asmaloney]

OK, thanks. If that's supposed to work I'll have to work on it some more to see what's going on.

I had tried switching the order as well, but I'm just getting a non-obvious parse error. I'm not sure how collapsing my two (working) patterns into one could result in ambiguity.

[asmaloney]

Ah, well. I was missing parens in the pattern. So it needs to look like this:

FooList []*foo `parser:"( '{' @@+ '} | @@ )'"`

That took far longer than it should have 😄