F# on Mono and Windows - discrepancy with simple function

Question

Can someone check my sanity here please. Given this simple function:

let filterOut item l =
  l |> List.filter (fun t -> not (t = item)) 

let f = 
  ["1";"2";"3"]
  |> filterOut "3"

Evaluating the above in FSI produces the following:

1. Xamarin Studio with mono 4.0.3 on Mac OS X

   val f : string list = ["1"]

2. Visual Studio 2013

   val f : string list = ["1"; "2"]

If the input is a list of ints or chars - then it works as expected and both platforms produce identical results. Also if I specify filterOut to only work with strings it correctly produces identical values. Like so:

 let filterOut item l:list<string> =
   l |> List.filter (fun t -> not (t = item)) 

Even the following code with XS on OS X:

let filterOut item l =
  l |> List.filter (fun t -> not (t = item)) 

let f = 
  ["1";"2";"3"]
  |> filterOut "foobar"

outputs:

val f : string list = ["1"]

I have compared the IL between the XS and VS compiled code and they appear identical. So it seems like a runtime discrepancy. If there something going on here with List.Filter and generic comparison with strings on Mono?

EDIT: If I add "inline" to the filterOut function I also get correct results on both platforms (expected output on OS X). Again it seems something is wrong with the generic comparer on the Mono runtime.

Answer 1

(1 month later) Tested on latest Mono 4.2.0 and now works as expected.