I have a library that defines a state monad, then uses it for a parser monad. Now I wanted to extend the parser state with a generic field that would be defined on usage of the library (e.g. for identifier lookup tables).

As this generic "payload" is mostly not used but just carried around, the compiler seems to have a hard time. And if I annotate all my functions with type variables, the computation expression fails because if overly infers the return type of the state monad.

On top of the the compiler keeps on trying to cast my functions arguments to "obj" types when I don't fully annotated them.

My easy way forwards is to give up genericity. But am I missing something about how to use F#? If I could parameterize the module I would just instantiate my library with the "right" generic type. Should I wrap things up with a class? But wouldn't that clash with the use of the compuration expression?

Anybody have a good idea?

FYI I get errors like:

Error 58 This code is not sufficiently generic. The type variable 'C could not be generalized because it would escape its scope.

Error 52 Type mismatch. Expecting a Parser<Env,'a> but given a StateRM.StateR,int,(PErr<obj> * PState<obj>)> The type 'Env' does not match the type 'obj'