require "./satisfy"

module Parcom
  # `Token` is a `Parser` that tries to parse a specific token
  # from the input stream.
  class Token(T) < Parser(T, T)
    # Accepts the token that this parser will try to parse.
    def initialize(@expected : T)
      @p = Satisfy(T).new { |x| x == @expected }
    end

    # Tries to parse the specified token from the input stream.
    def parse(tokens : Tokens(T)) : Result(T, T)
      @p.parse(tokens)
    rescue ex : ParserFail
      raise ParserFail.new("Token <#{@expected}>: #{ex.message}")
    end
  end
end