Building Abstractions with Data - Hierarchical Data and the Closure Property - Sequences as Conventional Interfaces - Sequence Operations - accumulate, polynomial, Horner's rule

Structure and Interpretation of Computer Programs: JavaScript Edition
楽天ブックス

開発環境

Structure and Interpretation of Computer Programs: JavaScript Edition(Harold Abelson(著)、Gerald Jay Sussman(著)、Julie Sussman(著)、The MIT Press)のChapter 2(Building Abstractions with Data)、2.2(Hierarchical Data and the Closure Property)、2.2.3(Sequences as Conventional Interfaces)、Sequence Operations、Exercise 2.34の解答を求めてみる。

コード

function stringfy(x) {
    if (is_null(x)) {
        return "null";
    }
    if (is_pair(x)) {
        return "[" + stringfy(head(x)) + ", " + stringfy(tail(x)) + "]";
    }
    return x.toString();
}
function pair(x, y) {
    return [x, y];
}
function head(z) {
    return z[0];
}
function tail(z) {
    return z[1];
}
function is_pair(x) {
    return Array.isArray(x);
}
function is_null(x) {
    return x === null;
}
function list(...args) {
    return args.length === 0 ?
        null :
        pair(args[0], list(...args.slice(1)));
}
function display(x) {
    return console.log(stringfy(x));
}
function accumulate(op, initial, sequence) {
    return is_null(sequence) ?
        initial :
        op(
            head(sequence),
            accumulate(op, initial, tail(sequence))
        );
}
function horner_eval(x, coefficient_sequence) {
    return accumulate(
        (this_coeff, higher_terms) =>
            this_coeff + higher_terms * x,
        0,
        coefficient_sequence
    );
}

display(
    horner_eval(2, list(1, 3, 0, 5, 0, 1))
);

const x = 2;
display(1 + 3 * x + 5 * x ** 3 + x ** 5);

入出力結果(Terminal, Zsh)

% node answer2.34.js
79
79
%