#ifndef L_PAREN
#	define L_PAREN '['
#endif

#ifndef R_PAREN
#	define R_PAREN ']'
#endif

/* psops(1) arguments are flanked by { '[', '\0' } and { ']', '\0' }. Nesting
 * is allowed to facilitate nesting of psops(1) programs. This checks to make
 * sure grouping symbols in args are balanced.
 * args is the argv that was passed to main, incremented (so args[1] is "[").
 * Returns 0 in the events of a syntax error or there being no arguments.
 * Otherwise, returns the number of top-level right grouping arguments
 * (i.e. the number of terms). */
int check_arg(char **args);

/* arg is the location of the argument with the left grouping symbol within
 * argv.
 * Returns the location of the argument with the corresponding left grouping
 * symbol within argv. */
char **corresponding_arg(char **arg);