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@jfairbank /build-list-1.js Secret
Last active Aug 29, 2015

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functional-javascript-lists-1
var list = new Cons(1, new Cons(3, new Cons(42, new Cons(28, Nil))));
var cons = function(head, tail) {
return new Cons(head, tail);
};
var list = cons(1, cons(3, cons(42, cons(28, Nil))));
var Cons = function(head, tail) {
this.head = head;
this.tail = tail;
};
Cons.prototype.isEmpty = false;
fib(4)
fib(3) + fib(2)
fib(2) + fib(1) + fib(1) + fib(0)
fib(1) + fib(0) + 1 + 1 + 0
1 + 0 + 1 + 1 + 0
3
function fib(n) {
if (n < 2) {
return n;
}
var n0 = 0;
var n1 = 1;
var ans = 0;
for (var i = 2; i <= n; i++) {
ans = n0 + n1;
n0 = n1;
n1 = ans;
}
return ans;
}
function fib(n) {
if (n < 2) {
return n;
}
return fib(n - 1) + fib(n - 2);
}
var myList = list(1, 3, 5);
//=> cons(1, cons(3, cons(5, Nil)));
var myOtherList = myList.map(n => n * 3);
//=> cons(3, cons(9, cons(15, Nil)));
var nine = myList.reduce((x, y) => x + y);
//=> 9
var listOfLists = list(list(1), list(2), list(3));
//=> cons(cons(1, Nil), cons(cons(2, Nil), cons(cons(3, Nil), Nil)));
var flattened = listOfLists.map(innerList => innerList.head);
//=> cons(1, cons(2, cons(3, Nil)));
var list = function () {
if (arguments.length === 0) {
return Nil;
}
var head = arguments[0];
var tail = [].slice.call(arguments, 1);
return cons(head, list.apply(null, tail));
};
var list = cons(1, cons(2, cons(3, Nil)));
var double = (n) => n * 2;
map(list, double); // yields:
cons(2, map(cons(2, cons(3, Nil)), double));
cons(2, cons(4, map(cons(3, Nil), double)));
cons(2, cons(4, cons(6, map(Nil, double))));
cons(2, cons(4, cons(6, Nil)));
var list = cons(1, cons(2, cons(3, Nil)));
var double = (n) => n * 2;
list.map(double); // cons(2, cons(4, cons(6, Nil)))
Cons.prototype.map = function(fn) {
return this.reduce((item) => cons(), Nil);
};
var map = function(list, fn) {
if (list.isEmpty) {
return list;
}
return cons(fn(list.head), map(list.tail, fn));
};
var Nil = {
isEmpty: true,
get head() {
throw new Error('Accessing head on empty list.');
},
get tail() {
throw new Error('Accessing tail on empty list.');
}
};
Cons.prototype.map = function (fn) {
var consBuilder = function(memo, value) {
return cons(fn(value), memo);
};
return this.reduceRight(consBuilder, Nil);
};
Cons.prototype.map = function(fn) {
return cons(fn(this.head), this.tail.map(fn));
};
Nil.map = function() {
return this;
};
Cons.prototype.reduce = function(fn, memo) {
return this.tail.reduce(fn, fn(memo, this.head));
};
Nil.reduce = function(fn, memo) {
return memo;
};
Cons.prototype.reduceRight = function(fn, memo) {
return fn(this.tail.reduceRight(fn, memo), this.head);
};
Nil.reduceRight = Nil.reduce;
var list = cons(1, cons(2, cons(3, Nil)));
var add = (x, y) => x + y;
reduce(list, add, 0); //=> 6
var reduce = function(list, fn, memo) {
if (list.isEmpty) {
return memo;
}
return reduce(list.tail, fn, fn(memo, list.head));
};
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