#!./txr
@(next :args)
@#
@# Define option_error exception, subtyped from error
@#
@(defex option_error error)
@#
@# Function for matching option that takes no argument
@#
@(define match_option (text opt_sym))
@  (cases)
@    (skip)
@    text
@    (bind opt_sym "y")
@  (or)
@    (bind opt_sym "n")
@  (end)
@(end)
@#
@# Function for matching option that takes an argument
@#
@(define match_option_arg (text opt_sym arg_sym))
@  (cases)
@    (skip)
@    text
@    arg_sym
@    (bind opt_sym "y")
@  (or)
@    (skip)
@    text
@    (throw option_error `@text requires arg`)
@  (or)
@    (bind opt_sym "n")
@  (end)
@(end)
@#
@# Main query
@#
@(try)
@  (maybe)
@    (match_option_arg "-a" opt_a opt_arg_a)
@  (or)
@    (match_option "-b" opt_b)
@  (or)
@    (match_option "-c" opt_c)
@  (end)
@  (maybe)
@    (bind opt_a "y")
@    (output)
option a was supplied, with argument @opt_arg_a
@    (end)
@  (or)
@    (bind opt_b "y")
@    (output)
option b was supplied
@    (end)
@  (or)
@    (bind opt_c "y")
@    (output)
option c was supplied
@    (end)
@  (end)
@(catch option_error (arg))
@(output)
error: @arg
@(end)
@(end)