static AST read_line = L("i", "f",
    let("p",
        A(y, L("read_line1", "i",
            A("i", L("j", "c",
                A(A(eq, "c", '\n'),
                    A(pair, "j", nil),
                    let("res",
                        A("read_line1", "j"),
                        A(pair,
                            A(fst, "res"),
                            A(pair,
                                "c",
                                A(snd, "res")))))))),
            "i"),
        A("f", A(fst, "p"), A(snd, "p"))));