[nem-en] void as type parameter

[Elifant]

Hello all.

In parsec library I have type Parser:

type Parser ['s, 't] = 's -> ParseResult['t]

i.e. it is a function which, given the state of type 's, returns result 
which may contain value of type 't.
It works good for parsing strings, characters and so on. By what type 
should 'eof' parser have?
Maybe some dummy type?

I know that 'void' was disabled to be used as type parameter some time 
ago. But I can't find
corresponding discussion. Can you give me a link?