Runtime crash with simple recursive grammar

[newlandsvalley]

I'm still finding this a wonderful parser. However, I've managed to crash the elm runtime with the error - cannot read property 'ctor' of undefined. I'm simply trying to parse lists of characters between brackets where the brackets can be nested - for example (AB (C D) E F). See this gist - https://gist.github.com/newlandsvalley/96dabd17480609ab4000. If I remove from the grammar the possibility of brackets being nested, the problem goes away.

It's strange because there's no such problem with your Calc example.

I suspect this is an Elm problem rather than a Combine one, but I thought I'd better post it here first.

[Bogdanp]

Elm is eagerly evaluated so in your example slur and slurContent end up creating a circular dependency that gets evaluated as soon as the output JS does, which means one function ends up calling the constructor of the other before the other is defined :). You can get around this using the rec combinator. For example you can rewrite slurContent to

slurContent : Parser Music
slurContent = rec <| \() -> choice [note , slur, spacer]

which should fix your problem.

[newlandsvalley]

Ah, of course - what wonderful support you give. Fixes the problem immediately.

[alech]

I had a very similar issue and the "rec <| () ->" trick solved it for me, too. I was wondering if this could be documented more clearly, for example in the documentation of "rec", since more people might stumble upon this.