index_gist.rb

      BEG_REGEXP = /\G(?:\
(?# 1:  SPACE   )( +)|\
(?# 2:  NIL     )(NIL)(?=[\x80-\xff(){ \x00-\x1f\x7f%*#{'"'}\\\[\]+])|\
(?# 3:  NUMBER  )(\d+)(?=[\x80-\xff(){ \x00-\x1f\x7f%*#{'"'}\\\[\]+])|\
(?# 4:  ATOM    )([^\x80-\xff(){ \x00-\x1f\x7f%*#{'"'}\\\[\]+]+)|\
(?# 5:  QUOTED  )"((?:[^\x00\r\n"\\]|\\["\\])*)"|\
(?# 6:  LPAR    )(\()|\
(?# 7:  RPAR    )(\))|\
(?# 8:  BSLASH  )(\\)|\
(?# 9:  STAR    )(\*)|\
(?# 10: LBRA    )(\[)|\
(?# 11: RBRA    )(\])|\
(?# 12: LITERAL )\{(\d+)\}\r\n|\
(?# 13: PLUS    )(\+)|\
(?# 14: PERCENT )(%)|\
(?# 15: CRLF    )(\r\n)|\
(?# 16: EOF     )(\z))/ni

# (?# 3:  NUMBER  ) removed - MRI && rbx throws error
# (?# 4:  ATOM    ) removed - MRI && rbx throws error
# (?# 16: EOF     ) removed - both returns 0 (Fixnum)

str = "K"

searched = str.index(BEG_REGEXP)
searched2 = str.index("K")

puts "return value for regex: #{searched}"
puts "return class for regex: #{searched.class}"
puts "return value for string: #{searched2}"
puts "return value for string: #{searched2.class}"