(documentation) who is "responsible for maintaining position" - Stream, token, or both?

[jwaldmann]

it seems to me that haddocks for Text.Parsec are contradictory w.r.t. the semantics of Stream s m t:

• https://hackage.haskell.org/package/parsec-3.1.18.0/docs/Text-Parsec.html#t:Stream "A Stream instance is responsible for maintaining the position within the stream in the stream state s" - indeed, since uncons only sees s

• https://hackage.haskell.org/package/parsec-3.1.18.0/docs/Text-Parsec.html#v:token "The source position of the t should be returned by posFromTok" - but this function's type (t -> SourcePos) does not mention s.

and that can only be solved by

• duplicating the position of the stream into the token? as the following example does, indeed: posFromTok (pos,t) = pos;
• or computing both representations of position independently - but synchronously, which seems fragile.

Forgive me if this is a basic design question, I stumbled on this when I wanted to write a custom Stream instance.