require "./parser.cr"

module Parcom
  # `Sequence` is a `Parser` that combines multiple parsers and
  # tries to parse all of them in succession. If all of the parsers
  # succeed, the values parsed are returned in an array, in the order
  # they were parsed in. If any of the parsers fail,
  # the `Sequence` also fails.
  class Sequence(T, V) < Parser(T, Array(V))
    # Accepts the parsers to use.
    def initialize(@ps : Iterable(Parser(T, V)))
    end

    # Tries each parser in order, and returns their results.
    # Fail if any of the wrapped parsers fail.
    # TODO: this can probably be optimised more for Arrays
    # TODO: might be better to use #zip
    def parse(tokens : Tokens(T)) : Result(T, Array(V))
      parsed = [] of V

      @ps.each do |p|
        r = p.parse(tokens)
        parsed << r.value
        tokens = r.tokens
      end

      Result.new(tokens, parsed)
    rescue ex : ParserFail
      raise ParserFail.new("Sequence: #{ex.message}")
    end
  end
end