How to define interdependent functions in F#?

Question

I defined these two functions in F#

let f t = 
   match t with
   |_ when t = 0 -> 1
   |_ -> g t-1

let g t = 1 + (f t)

However, F# compiler didn't accept it. It said that

stdin(9,16): error FS0039: The value or constructor 'f' is not defined

Please help me! Thanks.

Also, if you pasted just that into a blank `fsi` you will get a message about `g` being undefined. It is good to show the correct error message by starting a new `fsi` and rerunning all your code to ensure nothing is left from previous experiments — John Palmer, Sep 02 '13 at 10:47

John Palmer · Accepted Answer · 2013-09-02T10:24:24.280

5

F# supports mutual recusion using the let rec ... and ... syntax. Here is your example

let rec f t = 
   match t with
   |_ when t = 0 -> 1
   |_ -> g t-1

and g t = 1 + (f t)

edited Sep 02 '13 at 10:24

answered Sep 02 '13 at 10:16

John Palmer

1 Answers1