How can I correctly parse a String to Parser[Map[String,Any]] in Scala?

Question

Currently reading / working my way through "Programming in Scala, First Edition", specifically Chapter 31: Combinator Parsing

The author is describing how to parse a JSON file and offers the following more advanced tranformations:

def obj: Parser[Map[String, Any]] = // Can be improved
    "{"~repsep(member, ",")~"}" ^^ 
      { case "{"~ms~"}" => Map() ++ ms }

later improved to:

def obj: Parser[Map[String, Any]] =
    "{"~> repsep(member, ",") <~"}" ^^ (Map() ++ _)

However, when I enter such code into my IDE (IntelliJ IDEA 14.03), the compiler rejects it with:

Expression of type JSON.this.type#Parser[Iterable[Any]] doesn't conform to expected type JSON.this.type#Parser[Map[String,Any]]

I can, of course, make this error go away by changing obj's type to Parser[Iterable[Any]], but this doesn't give the desired result.

What is the correct way to do this?

For whatever it is worth, I'm using jdk 1.7.0_71 and sdk 2.11.5

Answer 1

It depends on the parser for "member". I guess you are using a parser like:

def member: Parser[Any]

Like in the example, try to use the member parser:

def member: Parser[(String, Any)] = 
    stringLiteral~":"~value ^^ 
      { case name~":"~value => (name, value) }