Error: The implementation async/cohttp_async.ml
# [...]
#            Request.t IO.t ->
#            (Response.t * [> `Pipe of bytes Async.Std.Pipe.Reader.t ]) IO.t
#        is not included in
#          val call_request :
#            ?interrupt:unit IO.t ->
#            ?body:Body.t -> Request.t -> (Response.t * Body.t) IO.t
#        File "async/cohttp_async.ml", line 195, characters 6-18:
#          Actual declaration