Question

I have just started with F# and functional programming. I want to know how I can make a function taking a tuple where I define that the first value have to be a string, instead of the standard int.

Example:

A function which replicates a string, s, n times and returns it. What i have right now is this:

let rec pow2 = function
    | (s:string,0) -> ""
    | (s:string,n) -> s + pow2(s,n-1)

This works, but I think that there is a better way than defining s:string every case.

(I know String.replicate, this is not for the sake of the effect, but learning)

Answer 1

In fact, no type annotations are required here. The "" return value in the the first pattern match is a sufficient enough hint for the compiler:

> let rec pow2 = function
    | (s,0) -> ""
    | (s,n) -> s + pow2(s,n-1);;

val pow2 : string * int -> string