The problem is that you're not defining print as a function but a constant value.

Functions should take at least one unit parameter:

open System

let repeat action count =
    for i in 1..count do
        action ()

let print () =
    printfn "Test"

repeat print 10

In your original code, the side-effect of printing happens only once, at the definition of print.

And there are no warnings as print it is used, but its value is (), which is the value returned by the printfn "test" function call.

let print =
    printfn "Test"

This is a binding. It means that variable print is assigned to result of execution of printfn "Test". Result of execution of printfnt "Test" is a unit (), which leads to following situation: print equals unit

In your loop you just return unit with each iteration, without actually calling anything.

To get desired results you need to change binding into a function:

open System

let repeat action count =
    for i in 1..count do
        action()

let print() =
    printfn "Test"

repeat print 10