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require "./parser.cr"
module Parcom
# `Map` is a `Parser` that tries to parse using another parser,
# and then changing the result of that parser to a different value.
#
# Example:
# ```
# # Where `Digits` is some parser that returns an array of digit characters
# parse_i32 = Digits.new.map { |x| x.join.to_i32 }
# result = parse_i32.parse(Tokens.from_string("1234"))
# result.value # => 1234 (Int32)
# ```
class Map(T, V, U) < Parser(T, U)
# Accepts the parser to use and the function to apply to the result.
def initialize(@p : Parser(T, V), &block : V -> U)
@f = block
end
# Tries to parse with the given parser and applies the
# function to the result if successful.
def parse(tokens : Tokens(T)) : Result(T, U)
result = @p.parse(tokens)
Result.new(result.tokens, @f.call(result.value))
rescue ex : ParserFail
raise ParserFail.new("Map: #{ex.message}")
end
end
end
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