{"ast_node_type":"variable","tokens":[{"end":71,"kind":"keyword","start":0,"text":"let"}]}
    let int0 = crate::num::codegen_checked_int_binop(fx, bin_op, a, b);
    // c + carry -> c + first intermediate carry or borrow respectively
    let c = int0.value_field(fx, FieldIdx::ZERO);