A regular expression for validating floating point numbers

float.rb

DIGITS   = '(\d+)'
EXPONENT = "([eE][+-]?#{DIGITS})"
SUFFIX   = '(f|F|d|D)'

PATTERN = Regexp.union [
                        "#{DIGITS}\\.#{DIGITS}?#{EXPONENT}?#{SUFFIX}?",
                        "\\.#{DIGITS}#{EXPONENT}?#{SUFFIX}?",
                        "#{DIGITS}#{EXPONENT}#{SUFFIX}?",
                        "#{DIGITS}#{EXPONENT}?#{SUFFIX}"
                       ].map { |str| Regexp.new "\\A#{str}\\Z" }