Very basic F# command line UI

basicUI.fs

//Very basic F# command line UI 
//trying to get a global state

open System

let mutable x = "NoUser"

let printPrompt () = 
    printfn "Current State: %s" x
    printf "command:>"

let getCommandLineInput _ =  
    printPrompt ()
    System.Console.ReadLine ()

let writeError value =
    printfn "ERROR - No Match\nYou typed: %s" value

let writeMatch value =
    printfn "Matched: %s" value
 
let processCommandLineInput commandLineInput =
    match commandLineInput with
    | "a" -> writeMatch "a"; x <- "Ivan"
    | "b" -> writeMatch "b"; x <- "Bob" 
    | "c" -> writeMatch "b" 
    | "exit" | "quit" -> Environment.Exit 55
    | _ -> writeError commandLineInput 
    //change to output a 'command'?

//let progLoop () =
//    let commandLineInput = Seq.initInfinite getCommandLineInput
//    Seq.iter processCommandLineInput commandLineInput
    
let progLoop () =
    getCommandLineInput
    |> Seq.initInfinite
    |> Seq.iter processCommandLineInput


[<EntryPoint>]
let main argv = 
    progLoop () 
    0


// big time help from 
// https://www.log4code.com/f-infinite-sequence-to-read-console-input/
// https://dev.to/integerman/creating-a-net-core-3-0-f-console-app-348h
// FoggyFinder -> https://forums.fsharp.org/t/basic-f-console-ui-program-loop/1216?u=ivanrainbolt

You could try something like this:

//Very basic F# command line UI 
//trying to get a global state

open System

let printPrompt state = 
    printfn "Current State: %s" state
    printf "command:>"

let getCommandLineInput state =  
    state |> printPrompt
    let input = Console.ReadLine()
    state, input 

let writeError value =
    value |> printfn "ERROR - No Match\nYou typed: %s" 

let writeMatch value =
    value |> printfn "Matched: %s" 
    
let processCommandLineInput state commandLineInput =
    match commandLineInput with
    | "a"            -> writeMatch("a")
                        Some("Ivan")
    
    | "b"            -> writeMatch("b")
                        Some("Bob")
    
    | "c"            -> writeMatch("b")
                        Some(state)
    
    | "exit"|"quit"  -> None

    | otherwise      -> writeError(otherwise)
                        Some(state)    

let rec progLoop state =
    state
    |>  getCommandLineInput
    ||> processCommandLineInput
    |>  function
        | Some newState -> newState |> progLoop
        | None          -> printfn "See ya!"

[<EntryPoint>]
let main _argv = 
    "NoUser" |> progLoop  
    0

Aaaand I just now saw the post on the fsharp community forums. Ahh, well...happy F#-ing! :)