zeroOrMore and optional don't seem to work as documented.

[fr-rustyphillips]

Using parboiled_2.12 v2.16

This:

 def TestZero: Rule1[Seq[String]] = rule (
    zeroOrMore(capture("aa"))
  )

and this:

 def TestZero: Rule1[Seq[String]] = rule (
    optional(oneOrMore(capture("aa")))
  )

Both produce this error: Expression of type Rule[HNil, StrictOut] doesn't conform to expected type Parboiled2.Rule1[Seq[String]]

In contrast, this does work:

 def TestZero: Rule1[Seq[String]] = rule (
    oneOrMore(capture("aa"))
  )

According to the docs, this type should work. Is there something different I should be doing for this to work?

[ljleb]

I am using the following class as a workaround for this issue:

implicit final class ArityRule[L](that: () => Rule1[L]) {
    def * : () => Rule1[Seq[L]] = () => rule {
        oneOrMore(that()) | push(Seq.empty[L])
    }

    def ? : () => Rule1[Option[L]] = () => rule {
        that() ~> Some.apply[L] _ | push(None)
    }
}

Please note this declaration uses meta rules: it requires that to be of type () => Rule[_, _] rather than Rule[_, _]. This requirement is stated in the README of parboiled2.

[sirthias]

Your first snippet:

def TestZero: Rule1[Seq[String]] = rule (
    zeroOrMore(capture("aa"))
  )

should compile fine. (It does for me, using Scala 2.12.8)

Your second snippet produces this compile error:

[error] ...: type mismatch;
[error]  found   : org.parboiled2.Rule[shapeless.HNil,Option[scala.collection.immutable.Seq[String]] :: shapeless.HNil]
[error]  required: org.parboiled2.Rule[shapeless.HNil,Seq[String] :: shapeless.HNil]
[error]       optional(oneOrMore(capture("aa")))

which explains the problem quite well, because the optional produces an Option, which your method result type doesn't contain.

How do you manage to have the compiler produce the error you've quoted?

[fr-rustyphillips]

Upon looking deeper, it looks like this problem is actually only one with the Scala plugins for Idea and Eclipse. It seems to actually compile fine.

Considering that basically everything else has worked flawlessly for me, I was under the impression that the tooling and the compiler were actually in sync. The workaround seems to work even when used with an IDE, so I'm probably going to go with that just so that I can continue to use the IDE for debugging purposes.

On Mon, Jun 24, 2019 at 8:38 AM Mathias notifications@github.com wrote:

Your first snippet:

def TestZero: Rule1[Seq[String]] = rule ( zeroOrMore(capture("aa")) )

should compile fine. (It does for me, using Scala 2.12.8)

Your second snippet produces this compile error:

[error] ...: type mismatch; [error] found : org.parboiled2.Rule[shapeless.HNil,Option[scala.collection.immutable.Seq[String]] :: shapeless.HNil] [error] required: org.parboiled2.Rule[shapeless.HNil,Seq[String] :: shapeless.HNil] [error] optional(oneOrMore(capture("aa")))

which explains the problem quite well, because the optional produces an Option, which your method result type doesn't contain.

How do you manage to have the compiler produce the error you've quoted?

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[sirthias]

Ok, thanks for digging up the source of the problem!