变量：传递、存取、变化。函数：传递、执行（结合）、操作。
函数作为参量、变量。
函数调用。
函数运算。
In computer science, function composition (not to be confused with object composition) is an act or mechanism to combine simple functions to build more complicated ones. Like the usual composition of functions in mathematics, the result of each function is passed as the argument of the next, and the result of the last one is the result of the whole.
https://en.wikipedia.org/wiki/Higher-order_function
https://en.wikipedia.org/wiki/Function_composition_(computer_science)