.ig
define a recursive macro that prints the recursion level,
then prints the input stack.  Eventually this should break
with an macro-recursion-too-deep error.

This assumes that the action file contains a line like this:
	req dump_stack eol dump-input-stack
(otherwise .dump_stack won't do anything)
..
.cp 0
.nr recursion_level 1 1
.\" define the macro
.de recurse
.tm recursion level is \\n[recursion_level]
.dump_stack
.nr recursion_level \\n[recursion_level]+1 1
.recurse
..
.\" invoke the macro
.recurse
