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Source file indexed_bind.ml

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module type LAWS = sig
  type ('a, 'index) t

  include Indexed_functor.LAWS with type ('a, 'index) t := ('a, 'index) t

  val bind_1 :
    unit -> (((('a, 'index) t, 'index) t, 'index) t, ('a, 'index) t) Law.t

  val bind_2 :
    unit -> ('a -> 'b, (('a, 'index) t, 'index) t -> ('b, 'index) t) Law.t

  val bind_3 :
       unit
    -> ( ('a, 'index) t
       , ('a -> ('b, 'index) t) -> ('b -> ('c, 'index) t) -> ('c, 'index) t )
       Law.t

  val bind_4 :
       unit
    -> ( 'a -> ('b, 'index) t
       ,    ('b -> ('c, 'index) t)
         -> ('c -> ('d, 'index) t)
         -> 'a
         -> ('d, 'index) t )
       Law.t
end

module For (B : Preface_specs.INDEXED_BIND) :
  LAWS with type ('a, 'index) t := ('a, 'index) B.t = struct
  open Law
  open Preface_core.Fun.Infix
  include Indexed_functor.For (B)

  let bind_1 () =
    let lhs x = B.(join % join) x
    and rhs x = B.(join % map join) x in

    law ("join % join" =~ lhs) ("join % map join" =~ rhs)
  ;;

  let bind_2 () =
    let lhs f x = B.(map f % join) x
    and rhs f x = B.(join % map (map f)) x in

    law ("map f % join" =~ lhs) ("join % map (map f)" =~ rhs)
  ;;

  let bind_3 () =
    let lhs x f g = B.(x >>= Infix.(fun y -> f y >>= g))
    and rhs x f g = B.(Infix.(x >>= f) >>= g) in

    law ("x >>= (fun y -> f y >>= g)" =~ lhs) ("(x >>= f) >>= g" =~ rhs)
  ;;

  let bind_4 () =
    let lhs f g h x = B.(Infix.(f >=> g) >=> h) x
    and rhs f g h x = B.(f >=> Infix.(g >=> h)) x in

    law ("(f >=> g) >=> h" =~ lhs) ("f >=> (g >=> h)" =~ rhs)
  ;;
end
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