Building Abstractions with Data - Symbolic Data - Example: Representing Sets - Sets as unordered lists - duplicates
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)、2.3(Symbolic Data)、2.3.3(Example: Representing Sets)、Sets as unordered lists、Exercise 2.60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)) + "]";
}
if (x === undefined) {
return "undefined";
}
return x.toString();
}
function display(x) {
return console.log(stringfy(x));
}
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 list(...args) {
return args.length === 0 ?
null :
pair(args[0], list(...args.slice(1)));
}
function is_null(x) {
return x === null;
}
function append(list1, list2) {
return is_null(list1) ?
list2 :
pair(head(list1), append(tail(list1), list2));
}
function equal(x, y) {
return is_null(x) && is_null(y)
? is_pair(x) && is_pair(y) && equal(head(x), head(y)) && equal(tail(x), tail(y))
: x === y;
}
function is_element_of_set(x, set) {
return is_null(set)
? false
: equal(x, head(set))
? true
: is_element_of_set(x, tail(set));
}
function adjoin_set(x, set) {
return pair(x, set);
}
function union_set(set1, set2) {
return append(set1, set2);
}
function intersection_set(set1, set2) {
return is_null(set1) || is_null(set2)
? null
: is_element_of_set(head(set1), set2)
? pair(head(set1), intersection_set(tail(set1), set2))
: intersection_set(tail(set1), set2);
}
const set1 = null;
const set2 = list(1, 3, 5, 7, 9);
const set3 = list(2, 4);
const set4 = list(1, 2, 3);
const sets = list(set1, set2, set3, set4);
function iter(sets1, sets2) {
function f(set, sets) {
if (!is_null(sets)) {
const set2 = head(sets);
display("set1");
display(set);
display("set2");
display(set2);
display("union");
display(union_set(set, set2));
display("intersection");
display(intersection_set(set, set2));
f(set, tail(sets));
}
}
if (!is_null(sets1)) {
const set = head(sets1);
f(set, sets2);
iter(tail(sets1), sets2);
}
}
iter(sets, sets);
入出力結果(Terminal, Zsh)
% node answer2.60.js
set1
null
set2
null
union
null
intersection
null
set1
null
set2
[1, [3, [5, [7, [9, null]]]]]
union
[1, [3, [5, [7, [9, null]]]]]
intersection
null
set1
null
set2
[2, [4, null]]
union
[2, [4, null]]
intersection
null
set1
null
set2
[1, [2, [3, null]]]
union
[1, [2, [3, null]]]
intersection
null
set1
[1, [3, [5, [7, [9, null]]]]]
set2
null
union
[1, [3, [5, [7, [9, null]]]]]
intersection
null
set1
[1, [3, [5, [7, [9, null]]]]]
set2
[1, [3, [5, [7, [9, null]]]]]
union
[1, [3, [5, [7, [9, [1, [3, [5, [7, [9, null]]]]]]]]]]
intersection
[1, [3, [5, [7, [9, null]]]]]
set1
[1, [3, [5, [7, [9, null]]]]]
set2
[2, [4, null]]
union
[1, [3, [5, [7, [9, [2, [4, null]]]]]]]
intersection
null
set1
[1, [3, [5, [7, [9, null]]]]]
set2
[1, [2, [3, null]]]
union
[1, [3, [5, [7, [9, [1, [2, [3, null]]]]]]]]
intersection
[1, [3, null]]
set1
[2, [4, null]]
set2
null
union
[2, [4, null]]
intersection
null
set1
[2, [4, null]]
set2
[1, [3, [5, [7, [9, null]]]]]
union
[2, [4, [1, [3, [5, [7, [9, null]]]]]]]
intersection
null
set1
[2, [4, null]]
set2
[2, [4, null]]
union
[2, [4, [2, [4, null]]]]
intersection
[2, [4, null]]
set1
[2, [4, null]]
set2
[1, [2, [3, null]]]
union
[2, [4, [1, [2, [3, null]]]]]
intersection
[2, null]
set1
[1, [2, [3, null]]]
set2
null
union
[1, [2, [3, null]]]
intersection
null
set1
[1, [2, [3, null]]]
set2
[1, [3, [5, [7, [9, null]]]]]
union
[1, [2, [3, [1, [3, [5, [7, [9, null]]]]]]]]
intersection
[1, [3, null]]
set1
[1, [2, [3, null]]]
set2
[2, [4, null]]
union
[1, [2, [3, [2, [4, null]]]]]
intersection
[2, null]
set1
[1, [2, [3, null]]]
set2
[1, [2, [3, null]]]
union
[1, [2, [3, [1, [2, [3, null]]]]]]
intersection
[1, [2, [3, null]]]
%