(*  Title:      HOL/Imperative_HOL/Heap_Monad.thy

    Author:     John Matthews, Galois Connections; Alexander Krauss, Lukas Bulwahn & Florian Haftmann, TU Muenchen

*)

header {* A monad with a polymorphic heap and primitive reasoning infrastructure *}

theory Heap_Monad

imports

  Heap

  "~~/src/HOL/Library/Monad_Syntax"

  "~~/src/HOL/Library/Code_Natural"

begin

subsection {* The monad *}

subsubsection {* Monad construction *}

text {* Monadic heap actions either produce values

  and transform the heap, or fail *}

datatype 'a Heap = Heap "heap \<Rightarrow> ('a \<times> heap) option"

lemma [code, code del]:

  "(Code_Evaluation.term_of :: 'a::typerep Heap \<Rightarrow> Code_Evaluation.term) = Code_Evaluation.term_of"

  ..

primrec execute :: "'a Heap \<Rightarrow> heap \<Rightarrow> ('a \<times> heap) option" where

  [code del]: "execute (Heap f) = f"

lemma Heap_cases [case_names succeed fail]:

  fixes f and h

  assumes succeed: "\<And>x h'. execute f h = Some (x, h') \<Longrightarrow> P"

  assumes fail: "execute f h = None \<Longrightarrow> P"

  shows P

  using assms by (cases "execute f h") auto

lemma Heap_execute [simp]:

  "Heap (execute f) = f" by (cases f) simp_all

lemma Heap_eqI:

  "(\<And>h. execute f h = execute g h) \<Longrightarrow> f = g"

    by (cases f, cases g) (auto simp: fun_eq_iff)

ML {* structure Execute_Simps = Named_Thms

(

  val name = @{binding execute_simps}

  val description = "simplification rules for execute"

) *}

setup Execute_Simps.setup

lemma execute_Let [execute_simps]:

  "execute (let x = t in f x) = (let x = t in execute (f x))"

  by (simp add: Let_def)

subsubsection {* Specialised lifters *}

definition tap :: "(heap \<Rightarrow> 'a) \<Rightarrow> 'a Heap" where

  [code del]: "tap f = Heap (\<lambda>h. Some (f h, h))"

lemma execute_tap [execute_simps]:

  "execute (tap f) h = Some (f h, h)"

  by (simp add: tap_def)

definition heap :: "(heap \<Rightarrow> 'a \<times> heap) \<Rightarrow> 'a Heap" where

  [code del]: "heap f = Heap (Some \<circ> f)"

lemma execute_heap [execute_simps]:

  "execute (heap f) = Some \<circ> f"

  by (simp add: heap_def)

definition guard :: "(heap \<Rightarrow> bool) \<Rightarrow> (heap \<Rightarrow> 'a \<times> heap) \<Rightarrow> 'a Heap" where

  [code del]: "guard P f = Heap (\<lambda>h. if P h then Some (f h) else None)"

lemma execute_guard [execute_simps]:

  "\<not> P h \<Longrightarrow> execute (guard P f) h = None"

  "P h \<Longrightarrow> execute (guard P f) h = Some (f h)"

  by (simp_all add: guard_def)

subsubsection {* Predicate classifying successful computations *}

definition success :: "'a Heap \<Rightarrow> heap \<Rightarrow> bool" where

  "success f h \<longleftrightarrow> execute f h \<noteq> None"

lemma successI:

  "execute f h \<noteq> None \<Longrightarrow> success f h"

  by (simp add: success_def)

lemma successE:

  assumes "success f h"

  obtains r h' where "r = fst (the (execute c h))"

    and "h' = snd (the (execute c h))"

    and "execute f h \<noteq> None"

  using assms by (simp add: success_def)

ML {* structure Success_Intros = Named_Thms

(

  val name = @{binding success_intros}

  val description = "introduction rules for success"

) *}

setup Success_Intros.setup

lemma success_tapI [success_intros]:

  "success (tap f) h"

  by (rule successI) (simp add: execute_simps)

lemma success_heapI [success_intros]:

  "success (heap f) h"

  by (rule successI) (simp add: execute_simps)

lemma success_guardI [success_intros]:

  "P h \<Longrightarrow> success (guard P f) h"

  by (rule successI) (simp add: execute_guard)

lemma success_LetI [success_intros]:

  "x = t \<Longrightarrow> success (f x) h \<Longrightarrow> success (let x = t in f x) h"

  by (simp add: Let_def)

lemma success_ifI:

  "(c \<Longrightarrow> success t h) \<Longrightarrow> (\<not> c \<Longrightarrow> success e h) \<Longrightarrow>

    success (if c then t else e) h"

  by (simp add: success_def)

subsubsection {* Predicate for a simple relational calculus *}

text {*

  The @{text effect} predicate states that when a computation @{text c}

  runs with the heap @{text h} will result in return value @{text r}

  and a heap @{text "h'"}, i.e.~no exception occurs.

*}  

definition effect :: "'a Heap \<Rightarrow> heap \<Rightarrow> heap \<Rightarrow> 'a \<Rightarrow> bool" where

  effect_def: "effect c h h' r \<longleftrightarrow> execute c h = Some (r, h')"

lemma effectI:

  "execute c h = Some (r, h') \<Longrightarrow> effect c h h' r"

  by (simp add: effect_def)

lemma effectE:

  assumes "effect c h h' r"

  obtains "r = fst (the (execute c h))"

    and "h' = snd (the (execute c h))"

    and "success c h"

proof (rule that)

  from assms have *: "execute c h = Some (r, h')" by (simp add: effect_def)

  then show "success c h" by (simp add: success_def)

  from * have "fst (the (execute c h)) = r" and "snd (the (execute c h)) = h'"

    by simp_all

  then show "r = fst (the (execute c h))"

    and "h' = snd (the (execute c h))" by simp_all

qed

lemma effect_success:

  "effect c h h' r \<Longrightarrow> success c h"

  by (simp add: effect_def success_def)

lemma success_effectE:

  assumes "success c h"

  obtains r h' where "effect c h h' r"

  using assms by (auto simp add: effect_def success_def)

lemma effect_deterministic:

  assumes "effect f h h' a"

    and "effect f h h'' b"

  shows "a = b" and "h' = h''"

  using assms unfolding effect_def by auto

ML {* structure Effect_Intros = Named_Thms

(

  val name = @{binding effect_intros}

  val description = "introduction rules for effect"

) *}

ML {* structure Effect_Elims = Named_Thms

(

  val name = @{binding effect_elims}

  val description = "elimination rules for effect"

) *}

setup "Effect_Intros.setup #> Effect_Elims.setup"

lemma effect_LetI [effect_intros]:

  assumes "x = t" "effect (f x) h h' r"

  shows "effect (let x = t in f x) h h' r"

  using assms by simp

lemma effect_LetE [effect_elims]:

  assumes "effect (let x = t in f x) h h' r"

  obtains "effect (f t) h h' r"

  using assms by simp

lemma effect_ifI:

  assumes "c \<Longrightarrow> effect t h h' r"

    and "\<not> c \<Longrightarrow> effect e h h' r"

  shows "effect (if c then t else e) h h' r"

  by (cases c) (simp_all add: assms)

lemma effect_ifE:

  assumes "effect (if c then t else e) h h' r"

  obtains "c" "effect t h h' r"

    | "\<not> c" "effect e h h' r"

  using assms by (cases c) simp_all

lemma effect_tapI [effect_intros]:

  assumes "h' = h" "r = f h"

  shows "effect (tap f) h h' r"

  by (rule effectI) (simp add: assms execute_simps)

lemma effect_tapE [effect_elims]:

  assumes "effect (tap f) h h' r"

  obtains "h' = h" and "r = f h"

  using assms by (rule effectE) (auto simp add: execute_simps)

lemma effect_heapI [effect_intros]:

  assumes "h' = snd (f h)" "r = fst (f h)"

  shows "effect (heap f) h h' r"

  by (rule effectI) (simp add: assms execute_simps)

lemma effect_heapE [effect_elims]:

  assumes "effect (heap f) h h' r"

  obtains "h' = snd (f h)" and "r = fst (f h)"

  using assms by (rule effectE) (simp add: execute_simps)

lemma effect_guardI [effect_intros]:

  assumes "P h" "h' = snd (f h)" "r = fst (f h)"

  shows "effect (guard P f) h h' r"

  by (rule effectI) (simp add: assms execute_simps)

lemma effect_guardE [effect_elims]:

  assumes "effect (guard P f) h h' r"

  obtains "h' = snd (f h)" "r = fst (f h)" "P h"

  using assms by (rule effectE)

    (auto simp add: execute_simps elim!: successE, cases "P h", auto simp add: execute_simps)

subsubsection {* Monad combinators *}

definition return :: "'a \<Rightarrow> 'a Heap" where

  [code del]: "return x = heap (Pair x)"

lemma execute_return [execute_simps]:

  "execute (return x) = Some \<circ> Pair x"

  by (simp add: return_def execute_simps)

lemma success_returnI [success_intros]:

  "success (return x) h"

  by (rule successI) (simp add: execute_simps)

lemma effect_returnI [effect_intros]:

  "h = h' \<Longrightarrow> effect (return x) h h' x"

  by (rule effectI) (simp add: execute_simps)

lemma effect_returnE [effect_elims]:

  assumes "effect (return x) h h' r"

  obtains "r = x" "h' = h"

  using assms by (rule effectE) (simp add: execute_simps)

definition raise :: "string \<Rightarrow> 'a Heap" where -- {* the string is just decoration *}

  [code del]: "raise s = Heap (\<lambda>_. None)"

lemma execute_raise [execute_simps]:

  "execute (raise s) = (\<lambda>_. None)"

  by (simp add: raise_def)

lemma effect_raiseE [effect_elims]:

  assumes "effect (raise x) h h' r"

  obtains "False"

  using assms by (rule effectE) (simp add: success_def execute_simps)

definition bind :: "'a Heap \<Rightarrow> ('a \<Rightarrow> 'b Heap) \<Rightarrow> 'b Heap" where

  [code del]: "bind f g = Heap (\<lambda>h. case execute f h of

                  Some (x, h') \<Rightarrow> execute (g x) h'

                | None \<Rightarrow> None)"

setup {*

  Adhoc_Overloading.add_variant 

    @{const_name Monad_Syntax.bind} @{const_name Heap_Monad.bind}

*}

lemma execute_bind [execute_simps]:

  "execute f h = Some (x, h') \<Longrightarrow> execute (f \<guillemotright>= g) h = execute (g x) h'"

  "execute f h = None \<Longrightarrow> execute (f \<guillemotright>= g) h = None"

  by (simp_all add: bind_def)

lemma execute_bind_case:

  "execute (f \<guillemotright>= g) h = (case (execute f h) of

    Some (x, h') \<Rightarrow> execute (g x) h' | None \<Rightarrow> None)"

  by (simp add: bind_def)

lemma execute_bind_success:

  "success f h \<Longrightarrow> execute (f \<guillemotright>= g) h = execute (g (fst (the (execute f h)))) (snd (the (execute f h)))"

  by (cases f h rule: Heap_cases) (auto elim!: successE simp add: bind_def)

lemma success_bind_executeI:

  "execute f h = Some (x, h') \<Longrightarrow> success (g x) h' \<Longrightarrow> success (f \<guillemotright>= g) h"

  by (auto intro!: successI elim!: successE simp add: bind_def)

lemma success_bind_effectI [success_intros]:

  "effect f h h' x \<Longrightarrow> success (g x) h' \<Longrightarrow> success (f \<guillemotright>= g) h"

  by (auto simp add: effect_def success_def bind_def)

lemma effect_bindI [effect_intros]:

  assumes "effect f h h' r" "effect (g r) h' h'' r'"

  shows "effect (f \<guillemotright>= g) h h'' r'"

  using assms

  apply (auto intro!: effectI elim!: effectE successE)

  apply (subst execute_bind, simp_all)

  done

lemma effect_bindE [effect_elims]:

  assumes "effect (f \<guillemotright>= g) h h'' r'"

  obtains h' r where "effect f h h' r" "effect (g r) h' h'' r'"

  using assms by (auto simp add: effect_def bind_def split: option.split_asm)

lemma execute_bind_eq_SomeI:

  assumes "execute f h = Some (x, h')"

    and "execute (g x) h' = Some (y, h'')"

  shows "execute (f \<guillemotright>= g) h = Some (y, h'')"

  using assms by (simp add: bind_def)

lemma return_bind [simp]: "return x \<guillemotright>= f = f x"

  by (rule Heap_eqI) (simp add: execute_bind execute_simps)

lemma bind_return [simp]: "f \<guillemotright>= return = f"

  by (rule Heap_eqI) (simp add: bind_def execute_simps split: option.splits)

lemma bind_bind [simp]: "(f \<guillemotright>= g) \<guillemotright>= k = (f :: 'a Heap) \<guillemotright>= (\<lambda>x. g x \<guillemotright>= k)"

  by (rule Heap_eqI) (simp add: bind_def execute_simps split: option.splits)

lemma raise_bind [simp]: "raise e \<guillemotright>= f = raise e"

  by (rule Heap_eqI) (simp add: execute_simps)

subsection {* Generic combinators *}

subsubsection {* Assertions *}

definition assert :: "('a \<Rightarrow> bool) \<Rightarrow> 'a \<Rightarrow> 'a Heap" where

  "assert P x = (if P x then return x else raise ''assert'')"

lemma execute_assert [execute_simps]:

  "P x \<Longrightarrow> execute (assert P x) h = Some (x, h)"

  "\<not> P x \<Longrightarrow> execute (assert P x) h = None"

  by (simp_all add: assert_def execute_simps)

lemma success_assertI [success_intros]:

  "P x \<Longrightarrow> success (assert P x) h"

  by (rule successI) (simp add: execute_assert)

lemma effect_assertI [effect_intros]:

  "P x \<Longrightarrow> h' = h \<Longrightarrow> r = x \<Longrightarrow> effect (assert P x) h h' r"

  by (rule effectI) (simp add: execute_assert)

lemma effect_assertE [effect_elims]:

  assumes "effect (assert P x) h h' r"

  obtains "P x" "r = x" "h' = h"

  using assms by (rule effectE) (cases "P x", simp_all add: execute_assert success_def)

lemma assert_cong [fundef_cong]:

  assumes "P = P'"

  assumes "\<And>x. P' x \<Longrightarrow> f x = f' x"

  shows "(assert P x >>= f) = (assert P' x >>= f')"

  by (rule Heap_eqI) (insert assms, simp add: assert_def)

subsubsection {* Plain lifting *}

definition lift :: "('a \<Rightarrow> 'b) \<Rightarrow> 'a \<Rightarrow> 'b Heap" where

  "lift f = return o f"

lemma lift_collapse [simp]:

  "lift f x = return (f x)"

  by (simp add: lift_def)

lemma bind_lift:

  "(f \<guillemotright>= lift g) = (f \<guillemotright>= (\<lambda>x. return (g x)))"

  by (simp add: lift_def comp_def)

subsubsection {* Iteration -- warning: this is rarely useful! *}

primrec fold_map :: "('a \<Rightarrow> 'b Heap) \<Rightarrow> 'a list \<Rightarrow> 'b list Heap" where

  "fold_map f [] = return []"

| "fold_map f (x # xs) = do {

     y \<leftarrow> f x;

     ys \<leftarrow> fold_map f xs;

     return (y # ys)

   }"

lemma fold_map_append:

  "fold_map f (xs @ ys) = fold_map f xs \<guillemotright>= (\<lambda>xs. fold_map f ys \<guillemotright>= (\<lambda>ys. return (xs @ ys)))"

  by (induct xs) simp_all

lemma execute_fold_map_unchanged_heap [execute_simps]:

  assumes "\<And>x. x \<in> set xs \<Longrightarrow> \<exists>y. execute (f x) h = Some (y, h)"

  shows "execute (fold_map f xs) h =

    Some (List.map (\<lambda>x. fst (the (execute (f x) h))) xs, h)"

using assms proof (induct xs)

  case Nil show ?case by (simp add: execute_simps)

next

  case (Cons x xs)

  from Cons.prems obtain y

    where y: "execute (f x) h = Some (y, h)" by auto

  moreover from Cons.prems Cons.hyps have "execute (fold_map f xs) h =

    Some (map (\<lambda>x. fst (the (execute (f x) h))) xs, h)" by auto

  ultimately show ?case by (simp, simp only: execute_bind(1), simp add: execute_simps)

qed

subsection {* Partial function definition setup *}

definition Heap_ord :: "'a Heap \<Rightarrow> 'a Heap \<Rightarrow> bool" where

  "Heap_ord = img_ord execute (fun_ord option_ord)"

definition Heap_lub :: "'a Heap set \<Rightarrow> 'a Heap" where

  "Heap_lub = img_lub execute Heap (fun_lub (flat_lub None))"

interpretation heap!: partial_function_definitions Heap_ord Heap_lub

proof -

  have "partial_function_definitions (fun_ord option_ord) (fun_lub (flat_lub None))"

    by (rule partial_function_lift) (rule flat_interpretation)

  then have "partial_function_definitions (img_ord execute (fun_ord option_ord))

      (img_lub execute Heap (fun_lub (flat_lub None)))"

    by (rule partial_function_image) (auto intro: Heap_eqI)

  then show "partial_function_definitions Heap_ord Heap_lub"

    by (simp only: Heap_ord_def Heap_lub_def)

qed

declaration {* Partial_Function.init "heap" @{term heap.fixp_fun}

  @{term heap.mono_body} @{thm heap.fixp_rule_uc} NONE *}

abbreviation "mono_Heap \<equiv> monotone (fun_ord Heap_ord) Heap_ord"

lemma Heap_ordI:

  assumes "\<And>h. execute x h = None \<or> execute x h = execute y h"

  shows "Heap_ord x y"

  using assms unfolding Heap_ord_def img_ord_def fun_ord_def flat_ord_def

  by blast

lemma Heap_ordE:

  assumes "Heap_ord x y"

  obtains "execute x h = None" | "execute x h = execute y h"

  using assms unfolding Heap_ord_def img_ord_def fun_ord_def flat_ord_def

  by atomize_elim blast

lemma bind_mono [partial_function_mono]:

  assumes mf: "mono_Heap B" and mg: "\<And>y. mono_Heap (\<lambda>f. C y f)"

  shows "mono_Heap (\<lambda>f. B f \<guillemotright>= (\<lambda>y. C y f))"

proof (rule monotoneI)

  fix f g :: "'a \<Rightarrow> 'b Heap" assume fg: "fun_ord Heap_ord f g"

  from mf

  have 1: "Heap_ord (B f) (B g)" by (rule monotoneD) (rule fg)

  from mg

  have 2: "\<And>y'. Heap_ord (C y' f) (C y' g)" by (rule monotoneD) (rule fg)

  have "Heap_ord (B f \<guillemotright>= (\<lambda>y. C y f)) (B g \<guillemotright>= (\<lambda>y. C y f))"

    (is "Heap_ord ?L ?R")

  proof (rule Heap_ordI)

    fix h

    from 1 show "execute ?L h = None \<or> execute ?L h = execute ?R h"

      by (rule Heap_ordE[where h = h]) (auto simp: execute_bind_case)

  qed

  also

  have "Heap_ord (B g \<guillemotright>= (\<lambda>y'. C y' f)) (B g \<guillemotright>= (\<lambda>y'. C y' g))"

    (is "Heap_ord ?L ?R")

  proof (rule Heap_ordI)

    fix h

    show "execute ?L h = None \<or> execute ?L h = execute ?R h"

    proof (cases "execute (B g) h")

      case None

      then have "execute ?L h = None" by (auto simp: execute_bind_case)

      thus ?thesis ..

    next

      case Some

      then obtain r h' where "execute (B g) h = Some (r, h')"

        by (metis surjective_pairing)

      then have "execute ?L h = execute (C r f) h'"

        "execute ?R h = execute (C r g) h'"

        by (auto simp: execute_bind_case)

      with 2[of r] show ?thesis by (auto elim: Heap_ordE)

    qed

  qed

  finally (heap.leq_trans)

  show "Heap_ord (B f \<guillemotright>= (\<lambda>y. C y f)) (B g \<guillemotright>= (\<lambda>y'. C y' g))" .

qed

subsection {* Code generator setup *}

subsubsection {* Logical intermediate layer *}

definition raise' :: "String.literal \<Rightarrow> 'a Heap" where

  [code del]: "raise' s = raise (explode s)"

lemma [code_abbrev]: "raise' (STR s) = raise s"

  unfolding raise'_def by (simp add: STR_inverse)

lemma raise_raise': (* FIXME delete candidate *)

  "raise s = raise' (STR s)"

  unfolding raise'_def by (simp add: STR_inverse)

code_datatype raise' -- {* avoid @{const "Heap"} formally *}

subsubsection {* SML and OCaml *}

code_type Heap (SML "unit/ ->/ _")

code_const bind (SML "!(fn/ f'_/ =>/ fn/ ()/ =>/ f'_/ (_/ ())/ ())")

code_const return (SML "!(fn/ ()/ =>/ _)")

code_const Heap_Monad.raise' (SML "!(raise/ Fail/ _)")

code_type Heap (OCaml "unit/ ->/ _")

code_const bind (OCaml "!(fun/ f'_/ ()/ ->/ f'_/ (_/ ())/ ())")

code_const return (OCaml "!(fun/ ()/ ->/ _)")

code_const Heap_Monad.raise' (OCaml "failwith")

subsubsection {* Haskell *}

text {* Adaption layer *}

code_include Haskell "Heap"

{*import qualified Control.Monad;

import qualified Control.Monad.ST;

import qualified Data.STRef;

import qualified Data.Array.ST;

import Natural;

type RealWorld = Control.Monad.ST.RealWorld;

type ST s a = Control.Monad.ST.ST s a;

type STRef s a = Data.STRef.STRef s a;

type STArray s a = Data.Array.ST.STArray s Natural a;

newSTRef = Data.STRef.newSTRef;

readSTRef = Data.STRef.readSTRef;

writeSTRef = Data.STRef.writeSTRef;

newArray :: Natural -> a -> ST s (STArray s a);

newArray k = Data.Array.ST.newArray (0, k);

newListArray :: [a] -> ST s (STArray s a);

newListArray xs = Data.Array.ST.newListArray (0, (fromInteger . toInteger . length) xs) xs;

newFunArray :: Natural -> (Natural -> a) -> ST s (STArray s a);

newFunArray k f = Data.Array.ST.newListArray (0, k) (map f [0..k-1]);

lengthArray :: STArray s a -> ST s Natural;

lengthArray a = Control.Monad.liftM snd (Data.Array.ST.getBounds a);

readArray :: STArray s a -> Natural -> ST s a;

readArray = Data.Array.ST.readArray;

writeArray :: STArray s a -> Natural -> a -> ST s ();

writeArray = Data.Array.ST.writeArray;*}

code_reserved Haskell Heap

text {* Monad *}

code_type Heap (Haskell "Heap.ST/ Heap.RealWorld/ _")

code_monad bind Haskell

code_const return (Haskell "return")

code_const Heap_Monad.raise' (Haskell "error")

subsubsection {* Scala *}

code_include Scala "Heap"

{*object Heap {

  def bind[A, B](f: Unit => A, g: A => Unit => B): Unit => B = (_: Unit) => g (f ()) ()

}

class Ref[A](x: A) {

  var value = x

}

object Ref {

  def apply[A](x: A): Ref[A] =

    new Ref[A](x)

  def lookup[A](r: Ref[A]): A =

    r.value

  def update[A](r: Ref[A], x: A): Unit =

    { r.value = x }

}

object Array {

  import collection.mutable.ArraySeq

  def alloc[A](n: Natural)(x: A): ArraySeq[A] =

    ArraySeq.fill(n.as_Int)(x)

  def make[A](n: Natural)(f: Natural => A): ArraySeq[A] =

    ArraySeq.tabulate(n.as_Int)((k: Int) => f(Natural(k)))

  def len[A](a: ArraySeq[A]): Natural =

    Natural(a.length)

  def nth[A](a: ArraySeq[A], n: Natural): A =

    a(n.as_Int)

  def upd[A](a: ArraySeq[A], n: Natural, x: A): Unit =

    a.update(n.as_Int, x)

  def freeze[A](a: ArraySeq[A]): List[A] =

    a.toList

}

*}

code_reserved Scala Heap Ref Array

code_type Heap (Scala "Unit/ =>/ _")

code_const bind (Scala "Heap.bind")

code_const return (Scala "('_: Unit)/ =>/ _")

code_const Heap_Monad.raise' (Scala "!error((_))")

subsubsection {* Target variants with less units *}

setup {*

let

open Code_Thingol;

fun imp_program naming =

  let

    fun is_const c = case lookup_const naming c

     of SOME c' => (fn c'' => c' = c'')

      | NONE => K false;

    val is_bind = is_const @{const_name bind};

    val is_return = is_const @{const_name return};

    val dummy_name = "";

    val dummy_case_term = IVar NONE;

    (*assumption: dummy values are not relevant for serialization*)

    val (unitt, unitT) = case lookup_const naming @{const_name Unity}

     of SOME unit' =>

          let

            val unitT = the (lookup_tyco naming @{type_name unit}) `%% []

          in

            (IConst { name = unit', typargs = [], dicts = [], dom = [],

              range = unitT, annotate = false }, unitT)

          end

      | NONE => error ("Must include " ^ @{const_name Unity} ^ " in generated constants.");

    fun dest_abs ((v, ty) `|=> t, _) = ((v, ty), t)

      | dest_abs (t, ty) =

          let

            val vs = fold_varnames cons t [];

            val v = singleton (Name.variant_list vs) "x";

            val ty' = (hd o fst o unfold_fun) ty;

          in ((SOME v, ty'), t `$ IVar (SOME v)) end;

    fun force (t as IConst { name = c, ... } `$ t') = if is_return c

          then t' else t `$ unitt

      | force t = t `$ unitt;

    fun tr_bind'' [(t1, _), (t2, ty2)] =

      let

        val ((v, ty), t) = dest_abs (t2, ty2);

      in ICase { term = force t1, typ = ty, clauses = [(IVar v, tr_bind' t)], primitive = dummy_case_term } end

    and tr_bind' t = case unfold_app t

     of (IConst { name = c, dom = ty1 :: ty2 :: _, ... }, [x1, x2]) => if is_bind c

          then tr_bind'' [(x1, ty1), (x2, ty2)]

          else force t

      | _ => force t;

    fun imp_monad_bind'' ts = (SOME dummy_name, unitT) `|=>

      ICase { term = IVar (SOME dummy_name), typ = unitT, clauses = [(unitt, tr_bind'' ts)], primitive = dummy_case_term }

    fun imp_monad_bind' (const as { name = c, dom = dom, ... }) ts = if is_bind c then case (ts, dom)

       of ([t1, t2], ty1 :: ty2 :: _) => imp_monad_bind'' [(t1, ty1), (t2, ty2)]

        | ([t1, t2, t3], ty1 :: ty2 :: _) => imp_monad_bind'' [(t1, ty1), (t2, ty2)] `$ t3

        | (ts, _) => imp_monad_bind (eta_expand 2 (const, ts))

      else IConst const `$$ map imp_monad_bind ts

    and imp_monad_bind (IConst const) = imp_monad_bind' const []

      | imp_monad_bind (t as IVar _) = t

      | imp_monad_bind (t as _ `$ _) = (case unfold_app t

         of (IConst const, ts) => imp_monad_bind' const ts

          | (t, ts) => imp_monad_bind t `$$ map imp_monad_bind ts)

      | imp_monad_bind (v_ty `|=> t) = v_ty `|=> imp_monad_bind t

      | imp_monad_bind (ICase { term = t, typ = ty, clauses = clauses, primitive = t0 }) =

          ICase { term = imp_monad_bind t, typ = ty,

            clauses = (map o pairself) imp_monad_bind clauses, primitive = imp_monad_bind t0 };

  in (Graph.map o K o map_terms_stmt) imp_monad_bind end;

in

Code_Target.extend_target ("SML_imp", ("SML", imp_program))

#> Code_Target.extend_target ("OCaml_imp", ("OCaml", imp_program))

#> Code_Target.extend_target ("Scala_imp", ("Scala", imp_program))

end

*}

hide_const (open) Heap heap guard raise' fold_map

end