(** * Type of generators *)

  (* begin GenType *)
  Inductive GenType (A:Type) : Type := MkGen : (nat -> RandomSeed -> A) -> GenType A.(** * Type of generators *)

  (* begin GenType *)
  Inductive GenType (A:Type) : Type := MkGen : (nat -> RandomSeed -> A) -> GenType A.(* end GenType *)
  
  Definition G := GenType.(** * Primitive generator combinators *)
  
  (* begin run *)
  Definition run {A : Type} (g : G A) := match g with MkGen f => f end.(* end run *)
  
  Definition returnGen {A : Type} (x : A) : G A :=
    MkGen (fun _ _ => x).Definition bindGen {A B : Type} (g : G A) (k : A -> G B) : G B :=
    MkGen (fun n r =>
             let (r1,r2) := randomSplit r in
             run (k (run g n r1)) n r2).Definition fmap {A B : Type} (f : A -> B) (g : G A) : G B :=
    MkGen (fun n r => f (run g n r)).Definition apGen {A B} (gf : G (A -> B)) (gg : G A) : G B :=
    bindGen gf (fun f => fmap f gg).Definition sized {A : Type} (f : nat -> G A) : G A :=
    MkGen (fun n r => run (f n) n r).Definition resize {A : Type} (n : nat) (g : G A) : G A :=
    match g with
    | MkGen m => MkGen (fun _ => m n)
    end.Definition promote {A : Type} (m : Rose (G A)) : G (Rose A) :=
    MkGen (fun n r => fmapRose (fun g => run g n r) m).Fixpoint rnds (s : RandomSeed) (n' : nat) : list RandomSeed :=
    match n' with
      | O => nil
      | S n'' =>
        let (s1, s2) := randomSplit s in
        cons s1 (rnds s2 n'')
    end.Fixpoint createRange (n : nat) (acc : list nat) : list nat :=
    match n with
      | O => List.rev (cons O acc)
      | S n' => createRange n' (cons n acc)
    end.Definition choose {A : Type} `{ChoosableFromInterval A} (range : A * A) : G A :=
    MkGen (fun _ r => fst (randomR range r)).Definition sample (A : Type) (g : G A) : list A :=
    match g with
      | MkGen m =>
        let rnd := newRandomSeed in
        let l := List.combine (rnds rnd 20) (createRange 10 nil) in
        List.map (fun (p : RandomSeed * nat) => let (r,n) := p in m n r) l
    end.(* LL : Things that need to be in GenLow because of MkGen *)
  
  Definition variant {A : Type} (p : SplitPath) (g : G A) : G A := 
    match g with 
      | MkGen f => MkGen (fun n r => f n (varySeed p r))
    end.Definition reallyUnsafeDelay {A : Type} : G (G A -> A) :=
    MkGen (fun r n g => (match g with MkGen f => f r n end)).Definition reallyUnsafePromote {r A : Type} (m : r -> G A) : G (r -> A) :=
    (bindGen reallyUnsafeDelay (fun eval => 
                                  returnGen (fun r => eval (m r)))).(* End Things *)

  (** * Semantics of generators *)

  (* Set of outcomes semantics definitions (repeated above) *)
  (* begin semGen *)
  Definition semGenSize {A : Type} (g : G A) (s : nat) : set A := codom (run g s).Definition semGenSizeOpt {A : Type} (g : G (option A)) (s : nat) : set A :=
    somes (semGenSize g s).Definition semGenOpt {A : Type} (g : G (option A)) : set A :=
    somes (semGen g).

Lemma bindGen_aux {A : Type} (g : G A) (n : nat) (r : RandomSeed) : semGen g (run g n r).