# Task
I often need to find the factorial of a number or the sum of all numbers up to a number when cheating on math tests. To help me with this, your task is to write $F$, a generalized version of those functions:
$$F(n) = 1 * 2 * \space ... \space * (n-1) * n$$
Please note that the operator $ * $ does not necessarily represent multiplication here, but stands for a [commutative](https://en.wikipedia.org/wiki/Commutative_property), [associative](https://en.wikipedia.org/wiki/Associative_property) operator that will be an input to your program/function. This means that $a * b$ is the same as $b * a$, and $a * (b * c)$ is the same as $(a * b) * c$. Its inputs are positive integers, and its outputs are integers.
# Rules
- $n$ will be a positive integer.
- $*$ is a binary function/operator that can be taken in any convenient format, including but not limited to:
- A function object
- A function pointer
- An object with a method with a specific name (e.g. Java's [`BiFunction`](https://docs.oracle.com/javase/8/docs/api/java/util/function/BiFunction.html[]()))
- A string that can be evaluated to get a function
- $*$ is a blackbox function. That means that you will not be able to examine it to see how it works; all you can do is feed it two positive integers and get an integer back.
- The output of your function will be an integer (not necessarily positive).
- This is <a class="badge is-tag">code golf</a>, so shortest code in bytes wins!
# Testcases
```
f | n | F(f, n)
Add | 1 | 1
Add | 5 | 15
Multiply | 1 | 1
Multiply | 5 | 120
XOR | 1 | 1
XOR | 2 | 3
XOR | 5 | 1
XOR | 10 | 11
```
Questions:
- Interesting enough? Is a vanilla factorial better?
- Are the tags okay?
- Needs more testcases?
- Input rules okay?
