Function handler_ty 

pub fn handler_ty() -> Expr

Handler : ∀ {Σ : EffectSig} {A B : Type}, EffectTree Σ A → (A → B) → (∀ op, Σ.arity op → (Σ.result op → B) → B) → B

Effect handler: interprets an effect tree using a pure return case and operation cases.