Quelle List_Cpo.thy Sprache: Isabelle

(*  Title:      HOL/HOLCF/Library/List_Cpo.thy
    Author:     Brian Huffman
*)

section \<open>Lists as a complete partial order\<close>

theory List_Cpo
imports HOLCF
begin

subsection \<open>Lists are a partial order\<close>

instantiation list :: (po) po
begin

definition
  "xs \ ys \ list_all2 (\) xs ys"

instance
proof
  fix xs ys zs :: "'a list"
  show "xs \ xs"
    using below_refl
    unfolding below_list_def
    by (rule list_all2_refl)
  show "xs \ ys \ ys \ zs \ xs \ zs"
    using below_trans
    unfolding below_list_def
    by (rule list_all2_trans)
  show "xs \ ys \ ys \ xs \ xs = ys"
    using below_antisym
    unfolding below_list_def
    by (rule list_all2_antisym)
qed

end

lemma below_list_simps [simp]:
  "[] \ []"
  "x # xs \ y # ys \ x \ y \ xs \ ys"
  "\ [] \ y # ys"
  "\ x # xs \ []"
by (simp_all add: below_list_def)

lemma Nil_below_iff [simp]: "[] \ xs \ xs = []"
by (cases xs, simp_all)

lemma below_Nil_iff [simp]: "xs \ [] \ xs = []"
by (cases xs, simp_all)

lemma list_below_induct [consumes 1, case_names Nil Cons]:
  assumes "xs \ ys"
  assumes 1: "P [] []"
  assumes 2: "\x y xs ys. \x \ y; xs \ ys; P xs ys\ \ P (x # xs) (y # ys)"
  shows "P xs ys"
using \<open>xs \<sqsubseteq> ys\<close>
proof (induct xs arbitrary: ys)
  case Nil thus ?case by (simp add: 1)
next
  case (Cons x xs) thus ?case by (cases ys, simp_all add: 2)
qed

lemma list_below_cases:
  assumes "xs \ ys"
  obtains "xs = []" and "ys = []" |
    x y xs' ys' where "xs = x # xs'" and "ys = y # ys'"
using assms by (cases xs, simp, cases ys, auto)

text "Thanks to Joachim Breitner"

lemma list_Cons_below:
  assumes "a # as \ xs"
  obtains b and bs where "a \ b" and "as \ bs" and "xs = b # bs"
  using assms by (cases xs, auto)

lemma list_below_Cons:
  assumes "xs \ b # bs"
  obtains a and as where "a \ b" and "as \ bs" and "xs = a # as"
  using assms by (cases xs, auto)

lemma hd_mono: "xs \ ys \ hd xs \ hd ys"
by (cases xs, simp, cases ys, simp, simp)

lemma tl_mono: "xs \ ys \ tl xs \ tl ys"
by (cases xs, simp, cases ys, simp, simp)

lemma ch2ch_hd [simp]: "chain (\i. S i) \ chain (\i. hd (S i))"
by (rule chainI, rule hd_mono, erule chainE)

lemma ch2ch_tl [simp]: "chain (\i. S i) \ chain (\i. tl (S i))"
by (rule chainI, rule tl_mono, erule chainE)

lemma below_same_length: "xs \ ys \ length xs = length ys"
unfolding below_list_def by (rule list_all2_lengthD)

lemma list_chain_induct [consumes 1, case_names Nil Cons]:
  assumes "chain S"
  assumes 1: "P (\i. [])"
  assumes 2: "\A B. chain A \ chain B \ P B \ P (\i. A i # B i)"
  shows "P S"
using \<open>chain S\<close>
proof (induct "S 0" arbitrary: S)
  case Nil
  have "\i. S 0 \ S i" by (simp add: chain_mono [OF \chain S\])
  with Nil have "\i. S i = []" by simp
  thus ?case by (simp add: 1)
next
  case (Cons x xs)
  have "\i. S 0 \ S i" by (simp add: chain_mono [OF \chain S\])
  hence *: "\i. S i \ []" by (rule all_forward, insert Cons) auto
  have "chain (\i. hd (S i))" and "chain (\i. tl (S i))"
    using \<open>chain S\<close> by simp_all
  moreover have "P (\i. tl (S i))"
    using \<open>chain S\<close> and \<open>x # xs = S 0\<close> [symmetric]
    by (simp add: Cons(1))
  ultimately have "P (\i. hd (S i) # tl (S i))"
    by (rule 2)
  thus "P S" by (simp add: *)
qed

lemma list_chain_cases:
  assumes S: "chain S"
  obtains "S = (\i. [])" |
    A B where "chain A" and "chain B" and "S = (\i. A i # B i)"
using S by (induct rule: list_chain_induct) simp_all

subsection \<open>Lists are a complete partial order\<close>

lemma is_lub_Cons:
  assumes A: "range A <<| x"
  assumes B: "range B <<| xs"
  shows "range (\i. A i # B i) <<| x # xs"
using assms
unfolding is_lub_def is_ub_def
by (clarsimp, case_tac u, simp_all)

instance list :: (cpo) cpo
proof
  fix S :: "nat \ 'a list"
  assume "chain S"
  then show "\x. range S <<| x"
  proof (induct rule: list_chain_induct)
    case Nil
    have "{[]} <<| []"
      by simp
    then obtain x :: "'a list" where "{[]} <<| x" ..
    then show ?case
      by auto
  next
    case (Cons A B) then show ?case
      by (auto intro: is_lub_Cons cpo_lubI)
  qed
qed

subsection \<open>Continuity of list operations\<close>

lemma cont2cont_Cons [simp, cont2cont]:
  assumes f: "cont (\x. f x)"
  assumes g: "cont (\x. g x)"
  shows "cont (\x. f x # g x)"
apply (rule contI)
apply (rule is_lub_Cons)
apply (erule contE [OF f])
apply (erule contE [OF g])
done

lemma lub_Cons:
  fixes A :: "nat \ 'a::cpo"
  assumes A: "chain A" and B: "chain B"
  shows "(\i. A i # B i) = (\i. A i) # (\i. B i)"
by (intro lub_eqI is_lub_Cons cpo_lubI A B)

lemma cont2cont_case_list:
  assumes f: "cont (\x. f x)"
  assumes g: "cont (\x. g x)"
  assumes h1: "\y ys. cont (\x. h x y ys)"
  assumes h2: "\x ys. cont (\y. h x y ys)"
  assumes h3: "\x y. cont (\ys. h x y ys)"
  shows "cont (\x. case f x of [] \ g x | y # ys \ h x y ys)"
apply (rule cont_apply [OF f])
apply (rule contI)
apply (erule list_chain_cases)
apply (simp add: is_lub_const)
apply (simp add: lub_Cons)
apply (simp add: cont2contlubE [OF h2])
apply (simp add: cont2contlubE [OF h3])
apply (simp add: diag_lub ch2ch_cont [OF h2] ch2ch_cont [OF h3])
apply (rule cpo_lubI, rule chainI, rule below_trans)
apply (erule cont2monofunE [OF h2 chainE])
apply (erule cont2monofunE [OF h3 chainE])
apply (case_tac y, simp_all add: g h1)
done

lemma cont2cont_case_list' [simp, cont2cont]:
  assumes f: "cont (\x. f x)"
  assumes g: "cont (\x. g x)"
  assumes h: "cont (\p. h (fst p) (fst (snd p)) (snd (snd p)))"
  shows "cont (\x. case f x of [] \ g x | y # ys \ h x y ys)"
using assms by (simp add: cont2cont_case_list prod_cont_iff)

text \<open>The simple version (due to Joachim Breitner) is needed if the
  element type of the list is not a cpo.\<close>

lemma cont2cont_case_list_simple [simp, cont2cont]:
  assumes "cont (\x. f1 x)"
  assumes "\y ys. cont (\x. f2 x y ys)"
  shows "cont (\x. case l of [] \ f1 x | y # ys \ f2 x y ys)"
using assms by (cases l) auto

text \<open>Lemma for proving continuity of recursive list functions:\<close>

lemma list_contI:
  fixes f :: "'a::cpo list \ 'b::cpo"
  assumes f: "\x xs. f (x # xs) = g x xs (f xs)"
  assumes g1: "\xs y. cont (\x. g x xs y)"
  assumes g2: "\x y. cont (\xs. g x xs y)"
  assumes g3: "\x xs. cont (\y. g x xs y)"
  shows "cont f"
proof (rule contI2)
  obtain h where h: "\x xs y. g x xs y = h\x\xs\y"
  proof
    fix x xs y show "g x xs y = (\ x xs y. g x xs y)\x\xs\y"
    by (simp add: cont2cont_LAM g1 g2 g3)
  qed
  show mono: "monofun f"
    apply (rule monofunI)
    apply (erule list_below_induct)
    apply simp
    apply (simp add: f h monofun_cfun)
    done
  fix Y :: "nat \ 'a list"
  assume "chain Y" thus "f (\i. Y i) \ (\i. f (Y i))"
    apply (induct rule: list_chain_induct)
    apply simp
    apply (simp add: lub_Cons f h)
    apply (simp add: lub_APP ch2ch_monofun [OF mono])
    apply (simp add: monofun_cfun)
    done
qed

text \<open>Continuity rule for map\<close>

lemma cont2cont_map [simp, cont2cont]:
  assumes f: "cont (\(x, y). f x y)"
  assumes g: "cont (\x. g x)"
  shows "cont (\x. map (\y. f x y) (g x))"
using f
apply (simp add: prod_cont_iff)
apply (rule cont_apply [OF g])
apply (rule list_contI, rule list.map, simp, simp, simp)
apply (induct_tac y, simp, simp)
done

text \<open>There are probably lots of other list operations that also
deserve to have continuity lemmas.  I'll add more as they are
needed.\<close>

subsection \<open>Lists are a discrete cpo\<close>

instance list :: (discrete_cpo) discrete_cpo
proof
  fix xs ys :: "'a list"
  show "xs \ ys \ xs = ys"
    by (induct xs arbitrary: ys, case_tac [!] ys, simp_all)
qed

subsection \<open>Compactness and chain-finiteness\<close>

lemma compact_Nil [simp]: "compact []"
apply (rule compactI2)
apply (erule list_chain_cases)
apply simp
apply (simp add: lub_Cons)
done

lemma compact_Cons: "\compact x; compact xs\ \ compact (x # xs)"
apply (rule compactI2)
apply (erule list_chain_cases)
apply (auto simp add: lub_Cons dest!: compactD2)
apply (rename_tac i j, rule_tac x="max i j" in exI)
apply (drule (1) below_trans [OF _ chain_mono [OF _ max.cobounded1]])
apply (drule (1) below_trans [OF _ chain_mono [OF _ max.cobounded2]])
apply (erule (1) conjI)
done

lemma compact_Cons_iff [simp]:
  "compact (x # xs) \ compact x \ compact xs"
apply (safe intro!: compact_Cons)
apply (simp only: compact_def)
apply (subgoal_tac "cont (\x. x # xs)")
apply (drule (1) adm_subst, simp, simp)
apply (simp only: compact_def)
apply (subgoal_tac "cont (\xs. x # xs)")
apply (drule (1) adm_subst, simp, simp)
done

instance list :: (chfin) chfin
proof
  fix Y :: "nat \ 'a list" assume "chain Y"
  moreover have "\(xs::'a list). compact xs"
    by (induct_tac xs, simp_all)
  ultimately show "\i. max_in_chain i Y"
    by (rule compact_imp_max_in_chain)
qed

subsection \<open>Using lists with fixrec\<close>

definition
  match_Nil :: "'a::cpo list \ 'b match \ 'b match"
where
  "match_Nil = (\ xs k. case xs of [] \ k | y # ys \ Fixrec.fail)"

definition
  match_Cons :: "'a::cpo list \ ('a \ 'a list \ 'b match) \ 'b match"
where
  "match_Cons = (\ xs k. case xs of [] \ Fixrec.fail | y # ys \ k\y\ys)"

lemma match_Nil_simps [simp]:
  "match_Nil\[]\k = k"
  "match_Nil\(x # xs)\k = Fixrec.fail"
unfolding match_Nil_def by simp_all

lemma match_Cons_simps [simp]:
  "match_Cons\[]\k = Fixrec.fail"
  "match_Cons\(x # xs)\k = k\x\xs"
unfolding match_Cons_def by simp_all

setup \<open>
  Fixrec.add_matchers
    [ (\<^const_name>\<open>Nil\<close>, \<^const_name>\<open>match_Nil\<close>),
      (\<^const_name>\<open>Cons\<close>, \<^const_name>\<open>match_Cons\<close>) ]
\<close>

end

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