Allow dashes in identfiers

[TomTheBear]

I have the case that one of my identifiers contains a -, like type-id. The parser fails because - is not an allowed rune in an identifier.

Example:

func main() {
    vars := map[string]interface{}{"type-id": "4"}
    expr := `type-id == "4"`
    e, err := gval.Full().NewEvaluable(expr)
    if err != nil {
        return
    }
    value, err := e.EvalBool(context.Background(), vars)
    if err != nil {
        return
    }
    fmt.Println(value)
}

I could open a PR, but the fix is so simple: Add the condition (pos > 0 && r == '-') to https://github.com/PaesslerAG/gval/blob/master/parser.go#L33 . The example works, I tested it even for multiple dashes. But I'm new to gval, so I might miss some cases.

[hoani]

I'm a bit late to the party, but it looks like we can do this ourselves now:

  lang := gval.NewLanguage(
    gval.Init(func(ctx context.Context, p *gval.Parser) (gval.Evaluable, error) {
      p.SetIsIdentRuneFunc(func(r rune, pos int) bool {
        return unicode.IsLetter(r) || r == '_' || (pos > 0 && unicode.IsDigit(r)) || (pos > 0 && r == '-')
      })
      return p.ParseExpression(ctx)
    }),
    gval.Full()
  )