Haskell State monad with tuples as state -


my apologies if question stupid (i'm still quite new monads), couldn't find answer far.

i want store pairs state in state monad. however, if try on simple example of (int, int) (ghci): 

prelude> import control.monad.state prelude control.monad.state> :t :: state int int :: state int int :: state int int prelude control.monad.state> :t :: state (int, int) int  <interactive>:1:1:     no instance (monadstate                        int (statet (int, int)  data.functor.identity.identity))       arising use of ‘get’     in expression: :: state (int, int) int

my questions are:
1. why?
2. how work?

the type of get is

get :: state s s

so if s = (int, int) want

get :: state (int, int) (int, int)

that's all. get returns entire tuple.


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