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require "./parser.cr"
require "./any_token.cr"
require "./assert.cr"
module Parcom
# `Satisfy` is a `Parser` that parses a single token
# if that token passes a predefined test, similar
# to `Assert`. This class is effectively a shorthand
# for the following:
# ```
# # These parsers are equivalent.
# letter_assert = Assert.new(AnyToken(Char).new) { |x| x.letter? }
# letter_satisfy = Satisfy(Char).new { |x| x.letter? }
# ```
class Satisfy(T) < Parser(T, T)
@p : Assert(T, T)
# Accepts the `Bool`-returning block containing the test
# to run on the parsed token.
def initialize(&block : T -> Bool)
@p = AnyToken(T).new.assert(&block)
end
# Returns the first token of the input if that
# token passes the test.
def parse(tokens : Tokens(T)) : Result(T, T)
@p.parse(tokens)
rescue ex : ParserFail
raise ParserFail.new("Satisfy: #{ex.message}")
end
end
end
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