Any difference between First Class Function and High Order Function
I'm wondering whether/what difference between First Class Function and High Order Function.
I read through those two wiki pages and they looks rather similar. If they talking about same, why need two terminologies?
Tried to google but have not found any useful thing.
Answer
There is a difference. When you say that a language has first-class functions, it means that the language treats functions as values – that you can assign a function into a variable, pass it around etc. Higher-order functions are functions that work on other functions, meaning that they take one or more functions as an argument and can also return a function.
The “higher-order” concept can be applied to functions in general, like functions in the mathematical sense. The “first-class” concept only has to do with functions in programming languages. It’s seldom used when referring to a function, such as “a first-class function”. It’s much more common to say that “a language has/hasn’t first-class function support”.
The two things are closely related, as it’s hard to imagine a language with first-class functions that would not also support higher-order functions, and conversely a language with higher-order functions but without first-class function support.