F＃递归函数退出？

Question

I am very new to F# programming. I am looking for an answer as to why the following recursive function will exit when the n=0 condition is reached. Does the "then 1" syntax have a special meaning that equates to EXIT?

let rec factorial n = 
    if n = 0 
    then 1 
    else n * factorial (n - 1)

Answer 1

Functional programming languages are expression oriented , as opposed to statement oriented. This means that everything is an expression that can be evaluated into a value.

The control flow structures, if and match , are also just expressions. The compiler checks that all branches of these expressions return the same type.

If you're familiar with the conditional ternary operator in other languages, F#'s expression if true then 1 else 0 , is equivalent to true ? 1 : 0 true ? 1 : 0 .

Furthermore, the function doesn't "exit" as such. It completes evaluation. Each instance of the function (there will be n + 1 instances) completes evaluation at the end of the if / then / else expression.