Demonstration of how non-tailcall warnings could work in F#

tailcall-warnings.fsx

// This code demonstrates how the F# compiler could detect and emit a warning
// for non-tail-recursive calls to help avoid stack overflows.
// In response to: http://fslang.uservoice.com/forums/245727-f-language/suggestions/5663074-enable-a-compiler-warning-when-a-recursive-algorit

module Blah

let foo x =
    printfn "Foo: %x" x

let rec bar x =
    match x with
    | 0 ->
        foo x           // OK: non-tail-recursive call to a function which doesn't share the current stack frame (i.e., 'bar' or 'baz').
        printfn "Zero"
        
    | 1 ->
        bar (x - 1)     // Warning: this call is not tail-recursive
        printfn "Uno"
        baz x           // OK: tail-recursive call.

    | x ->
        printfn "0x%08x" x
        bar (x - 1)     // OK: tail-recursive call.
        
and baz x =
    printfn "Baz!"
    bar (x - 1)         // OK: tail-recursive call.