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require "./parser.cr"
require "./optional.cr"
require "./map.cr"
module Parcom
# `Recover` is a `Parser` that tries to parse with another parser,
# but does not fail the parser chain if the wrapped parser fails.
# If the wrapped parser fails, a `Recover` will not modify the input
# stream, and return an arbitrary value of type `V` instead.
class Recover(T, V) < Parser(T, V)
@p : Map(T, V?, V)
# Accepts the parser to use, and the default value
# to return if the parser fails.
def initialize(p : Parser(T, V), default : V)
@p = Optional.new(p).map { |x| x.nil? ? default : x }
end
# Tries to parse with the given parser, succeeds with the
# default value instead of failing. This parser does not
# consume input if the wrapped parser fails.
def parse(tokens : Tokens(T)) : Result(T, V)
@p.parse(tokens)
end
end
end
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