@top T { expr* }

expr[@isGroup=Expression] {
  atom |
  ParenExpr { "(" expr ")" }
}

atom { Id | Number }

@tokens {
  Id { "a"+ }
  Number { "1"+ }
  "(" ")"
}

# Adds the group prop

a(1)

==> T(Id[group=Expression],ParenExpr[group=Expression]("(", Number[group=Expression], ")"))
