F# command line (fsi) doesn't recognize function, compile error, why?

Question

I tried F# under command line, it doesn't recognize function definition

> let ref f n=
-  if(n<=2)then 1
-  else f(n-1)+f(n-2)
- ;;

val ref : f:(int -> int) -> n:int -> int

> printf "%i" (f 10)
- ;;

  printf "%i" (f 10)
  -------------^

stdin(9,14): error FS0039: The value or constructor 'f' is not defined

Question: any error in my program? I copied and pasted the definition and usage of f into visual studio's F# project, it runs OK.

But Why command line fails?

Answer 1

You defined a function named ref, but you're trying to call a function named f. No such function was defined (though your ref function takes a parameter named f), so you can't call it.

You probably intended to define a recursive function f using the rec keyword (with a 'c'), rather than defining a function named ref.

I copied and pasted the definition and usage of f into visual studio's F# project, it runs OK.

That's only possible if your VS project already contains a definition of a function named f.