documentation for the macro "balanced_parentheses"

Checks if parentheses are balanced in non-m4 code

It is defined in the file build.m4.

m4 code:

define(`balanced_parentheses',
`define(`_policy_makefile_increments',`
check_balanced_parentheses:` $(SOURCE_BALANCED)'`'`
patsubst(`',^,
`	')'
'_policy_makefile_increments)dnl
define(`_policy_tests',_policy_tests`\
		check_balanced_parentheses')')