Unable to call a function from recursive f# - f#

Question

trying out F#, learnt a lot today not sure if I am doing this try but I have a pattern match and recursive for some reason I am unable to call this from recursive.
// Define my active recognizer for keywords
let(|MyGirlFriend|Bye|) input =
match input with
|"lonely|"love"|"friendship"
-> MyGirlFriend
|"goodbye"|"bye"|"go"|
-> Bye
|_
-> None
I think the above code that above looks right.
//recursive response function
let rec response (token: string) (str: string) =
match token with
| Bye
-> good_bye_response ()
| RoomLocation
-> sprintf "%s" "Your call is log. Do you wish to quit?"
|_ when token.Contains("yes") -> "good bye" 0
|_ when token.Contains("no") -> answer_response ()
| None when (str.IndexOf(" ") > 0)
-> response (str.Substring(0,str.IndexOf(" ")))
(str.Substring(str.IndexOf(" ")+1))
| None when (str.IndexOf(" ") < 0)
-> response str ""
my function is :
let rec chat () =
if Break = false then
let valueInput = Console.ReadLine()
printf "Helpdesk-BCU Response --> %s \n" (response "" valueInput)
if Break = false then
chat()
else
ChatEnd()
let BCU_response (str: string) =
if (str.IndexOf(" ") > 0) then
response (str.Substring(0,str.IndexOf(" "))) (str.Substring(str.IndexOf("
")+1)) + "\n"
else
response str "" + "\n"
a couple of issues here |_ when token.Contains("yes") -> "goodbye" 0 the zero that is used in F# as an exit on here I get a red line and it states expression should have type string but has type int, I know zero is an int.
so how do I exit the recursive loop?
any sugguestion would be most welcome

Answer 1

It is not entirely clear what part are you struggling with, because there is quite a lot of minor issues in the code. However, a minimal working example that shows how to do the recursion is something like this:
open System
let (|Bye|Other|) input =
match input with
| "goodbye" | "bye" | "go" -> Bye
| _ -> Other
let response (token: string) =
match token with
| Bye -> false, "bye!"
| Other -> true, "sorry, I didn't get that"
let rec chat () =
let input = Console.ReadLine()
let keepRunning, message = response input
printfn ">> %s" message
if keepRunning then chat ()
The response function now also returns a Boolean - if this is true, the chat function calls itself recursively to ask another question. Otherwise, it just returns without asking more questions.