Eloquent Javascript:高阶函数示例 [英] Eloquent Javascript: Higher Order Functions example
问题描述
function reduceAncestors(person, f, defaultValue) {
function valueFor(person) {
if (person == null)
return defaultValue;
else
return f(person, valueFor(byName[person.mother]),
valueFor(byName[person.father]));
}
return valueFor(person);
}
function sharedDNA(person, fromMother, fromFather) {
if (person.name == "Pauwels van Haverbeke")
return 1;
else
return (fromMother + fromFather) / 2;
}
var ph = byName["Philibert Haverbeke"];
console.log(reduceAncestors(ph, sharedDNA, 0) / 4);
// → 0.00049
我在Eloquent Javascript中理解这个例子时遇到了很多麻烦。这是高阶函数章节(第5章)末尾的例子,在Great-Great-Great ...标题下,我没有看到fromMother和fromFather在哪里得到他们的价值观。我认为他们指的是valueFor(byName [person.mother]和valueFor(byName [person.father]),但我不知道valueFor函数是如何或何时从数据中检索实际数字值(请注意,我显然没有在这篇文章中包含数据,也没有包含byName函数。)提前感谢任何帮助!
I am having a lot of trouble understanding this example from Eloquent Javascript. This is the example at the end of the Higher Order Functions Chapter (chpt 5), under the heading "Great-Great-Great..." I don't see where fromMother and fromFather are getting their values. I think that they are referring to valueFor(byName[person.mother] and valueFor(byName[person.father]), but I don't see how or when the "valueFor" functions ever retrieve an actual number value from the data (note that I obviously didn't include the data in this post, nor did I include the byName function). Thanks in advance for any help!
推荐答案
reduceAncestors(ph,sharedDNA,0)/ 4)
将 sharedDNA
函数作为第二个参数传递。
reduceAncestors(ph, sharedDNA, 0) / 4)
passes the sharedDNA
function as the second argument.
它被分配到 f
这里:
function reduceAncestors(person, f, defaultValue)
<$在这里调用c $ c> f :
f(person, valueFor(byName[person.mother]), valueFor(byName[person.father]));
...在那里你可以看到从母亲那里分配给的第二个和第三个参数
和 fromFather
:
… where you can see the second and third arguments which get assigned to fromMother
and fromFather
:
function sharedDNA(person, fromMother, fromFather) {
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