End Map.
Section MonadProofs.
Context {K : Type}.
Context {V : Type}.
Context `{DecEq K}.
Definition St : Type := Map K V.
Definition read (k : K) : State St (option V) :=
bind get (fun st =>
ret (lookup k st)).
Definition write (k : K) (v : V) : State St unit :=
bind get (fun st =>
put (insert k v st)).
Definition write_and_read (k : K) (v : V) : State St (option V) :=
bind (write k v) (fun _ =>
read k).

Theorem write_and_read_correct (k : K) (v : V) (s : St) :
well_formed s ->
fst (write_and_read k v s) = Some v.