cx_or
lhs = expr_eval(expr->cx_or.left, fn, ctx);
rhs = expr_eval(expr->cx_or.right, fn, ctx);
cx->cx_or.left = left;
cx->cx_or.right = right;
cx->cx_or.left = NULL;
cx->cx_or.right = NULL;
condexpr_destroy(expr->cx_or.left);
condexpr_destroy(expr->cx_or.right);