Building Abstractions with Functions - Formulating Abstractions with Higher-Order Functions - Functions as Arguments - accumlate function, recursive process, iterative process
Structure and Interpretation of Computer Programs: JavaScript Edition(Harold Abelson(著)、Gerald Jay Sussman(著)、Julie Sussman(著)、The MIT Press)のChapter 1(Building Abstractions with Functions)、1.3(Formulating Abstractions with Higher-Order Functions)、1.3.1(Functions as Arguments)、Exercise 1.32の解答を求めてみる。
コード
function add(x, y) {
return x + y;
}
function mul(x, y) {
return x * y;
}
function inc(x) {
return x + 1;
}
function identity(x) {
return x;
}
function add2(x) {
return x + 2;
}
function double(x) {
return 2 * x;
}
console.log('a.')
function accumulate_recursive(combiner, null_value, term, a, next, b) {
return a > b ?
null_value :
combiner(
term(a),
accumulate_recursive(combiner, null_value, term, next(a), next, b)
);
}
function sum_recursive(term, a, next, b) {
return accumulate_recursive(add, 0, term, a, next, b);
}
function product_recursive(term, a, next, b) {
return accumulate_recursive(mul, 1, term, a, next, b);
}
console.log(sum_recursive(identity, 1, inc, 10));
console.log(sum_recursive(identity, 1, add2, 10));
console.log(sum_recursive(identity, 2, add2, 10));
console.log();
console.log(sum_recursive(double, 1, inc, 10));
console.log(sum_recursive(double, 1, add2, 10));
console.log(sum_recursive(double, 2, add2, 10));
console.log();
console.log(product_recursive(identity, 1, inc, 10));
console.log(product_recursive(identity, 1, add2, 10));
console.log(product_recursive(identity, 2, add2, 10));
console.log();
console.log(product_recursive(double, 1, inc, 10));
console.log(product_recursive(double, 1, add2, 10));
console.log(product_recursive(double, 2, add2, 10));
console.log();
console.log('b.');
function accumulate(combiner, null_value, term, a, next, b) {
function iter(n, result) {
return n > b ?
result :
iter(next(n), combiner(result, term(n)));
}
return iter(a, null_value);
}
function sum(term, a, next, b) {
return accumulate(add, 0, term, a, next, b);
}
function product(term, a, next, b) {
return accumulate(mul, 1, term, a, next, b);
}
console.log(sum(identity, 1, inc, 10));
console.log(sum(identity, 1, add2, 10));
console.log(sum(identity, 2, add2, 10));
console.log();
console.log(sum(double, 1, inc, 10));
console.log(sum(double, 1, add2, 10));
console.log(sum(double, 2, add2, 10));
console.log();
console.log(product(identity, 1, inc, 10));
console.log(product(identity, 1, add2, 10));
console.log(product(identity, 2, add2, 10));
console.log();
console.log(product(double, 1, inc, 10));
console.log(product(double, 1, add2, 10));
console.log(product(double, 2, add2, 10));
console.log();
入出力結果(Terminal, Zsh)
% node answer1.32.js
a.
55
25
30
110
50
60
3628800
945
3840
3715891200
30240
122880
b.
55
25
30
110
50
60
3628800
945
3840
3715891200
30240
122880
%