let result env =
match env.result, env.return with
| Some x, Some t -> x, t
| Some _, _ -> Wp_parameters.fatal "Result type undefined"
| None ,_ ->
match env.return with
| Some typ ->
let x = D.fresh "result" (Mdata.Vacsl (Ctype typ)) in
env.result <- Some x ; (x, typ)
| None ->
Wp_parameters.fatal "Result type undefined"