MKF2
| cond_or_expr '|' cond_and_expr { $$ = MKF2(cx, or, $1, $3); }
| cond_and_expr '&' cond_prefix_expr { $$ = MKF2(cx, and, $1, $3); }
value { $$ = MKF2(loc, val, $1, NULL); }
| value ',' values { $$ = MKF2(loc, val, $1, $3); }