Case class, Parser Action and optional combinator

[Vladimir Ivanov]

Hi, I have newbie question about parboiled2.

Having following simple case class and rule definitions:

case class Expr(value: Char)

def Expression = rule { optional(ch('+') | ch('*') ~> (Expr(_: Char))) }

I'm getting following error whenever I try to use `optional`, `zeroOrMore`, `oneOrMore` and `times` combinators with Parser Action to create case class (part of AST):  

[error]  The `optional`, `zeroOrMore`, `oneOrMore` and `times` modifiers can only be used on rules of type `Rule0`, `Rule1[T]` and `Rule[I, O <: I]`!

[error]   def Expression = rule  { optional(ch('+') | ch('*') ~> ((c: Char) => Expr(c))) }

I tried to move optional up in the rule tree or explicitly specify type parameters for Rule type with Shapeless HList (like Rule[Char :: HNil, Expr :: HNil]), but got the same result.

Could someone please help with this problem?

Thanks,

Vladimir

[Alexander Myltsev]

Hi,

You're missing `capture`. Try this one: 

def Expression = rule { optional(capture(CharPredicate("+*"))) ~> ((op: Option[String]) => ???) }

On Monday, 27 July 2015 23:41:04 UTC+3, Vladimir Ivanov wrote:

Hi, I have newbie question about parboiled2.

Having following simple case class and rule definitions:

case class Expr(value: Char)

def Expression = rule { optional(capture(ch('+') | ch('*') ~> (Expr(_: Char))) }

[Vladimir Ivanov]

Hi Alexander,

Many thanks for you reply and explanation! Works like a charm.

Vladimir

вторник, 28 июля 2015 г., 4:57:40 UTC-4 пользователь Alexander Myltsev написал: