/ StateT / modify
modify
 1      let Monad = ./../Monad/Type
 2  
 3  in  let StateMonad = ./monad
 4  
 5  in    λ(s : Type)
 6      → λ(m : Type → Type)
 7      → λ(monad : Monad m)
 8      → λ(f : s → s)
 9      →     let bind = (StateMonad s m monad).bind
10        
11        in  bind s {} (./get s m monad) (λ(state : s) → ./put s m monad (f state))