Factorial in M4

Welcome to the Factorial in M4 page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

divert(-1)
define(`show_usage',
`Usage: please input a non-negative integer
m4exit(`1')')

dnl is_valid(n)
define(`is_valid', `eval(regexp(`$1', `^\s*-?[0-9]+\s*$') >= 0)')

dnl factorial(n)
define(`factorial', `ifelse(eval(`$1' <= 1), 1, 1, `eval($1 * factorial(decr($1)))')')
divert(0)dnl
ifelse(eval(ARGC < 1 || len(ARGV1) < 1 || !is_valid(ARGV1)), 1, `show_usage()')dnl
ifelse(eval(ARGV1 < 0), 1, `show_usage()', `factorial(ARGV1)')

Factorial in M4 was written by:

• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

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How to Run the Solution

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