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require "./parser.cr"
module Parcom
# `EOF` is a `Parser` succeeds if the input stream is empty.
#
# This parser retuns `nil` when successful because there is no
# other meaningful value to return.
#
# This parser is also one of the few cases where it is ideal to not
# modify or take from the input stream, as it should be empty anyway.
class EOF(T) < Parser(T, Nil)
# Succeeds is the input stream is empty and returns `nil`.
# Raises a `ParserFail` exception when the input is not empty.
def parse(tokens : Tokens(T)) : Result(T, Nil)
if tokens.empty?
Result.new(tokens, nil)
else
raise ParserFail.new("Eof: input was not empty")
end
end
end
end
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