show not working for certain types

[apuccia]

I'm doing a school project in which I have some types annotated with show and other plugins, as an example:

and 'a lvalue_node =
  | AccVar of identifier option * identifier 
  | AccIndex of 'a lvalue * 'a expr (* here also expr derives show, ord, eq *) 
[@@deriving show, ord, eq]

Now, I'm trying to use the corresponding show function but I get the following error:

Error: This expression has type 'a lvalue_node
       but an expression was expected of type Format.formatter -> 'b -> unit

[apuccia]

I solved the problem. Simply I had to pass to show_lvalue_node also the pp_* function of the type parameter used.