F# ToString() %A formatting doesnt work on linux with mono

Question

I use the fsharpc compiler installed with mono. And I wanted to override the ToString() method for some of my types. The thing is it all compiles just fine but printf "%A" just gives me the default debug output. So to make absolutly sure i didnt miss something, I wrote a simple test on try.fsharp.org and compiled the same code myself. Still just getting default formatting

So is there something missing from the .net framework or something?

Answer 1

To ensure that printf calls ToString() , use %O format instead of %A :

type MyType =
    {
        MyValue : string
    }
    override __.ToString() = "Hello!"

[<EntryPoint>]
let main argv =  
    let record = { MyValue = "A value" }
    printfn "%A" record   // { MyValue = "A value" }
    printfn "%O" record   // Hello!
    0

See this link for details.