author | huffman |
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changeset 16463 | 342d74ca8815 |
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permissions | -rw-r--r-- |
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(* Title: HOLCF/Fixrec.thy |
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ID: $Id$ |
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Author: Amber Telfer and Brian Huffman |
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*) |
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header "Package for defining recursive functions in HOLCF" |
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theory Fixrec |
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imports Ssum One Up Fix Tr |
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uses ("fixrec_package.ML") |
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begin |
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subsection {* Maybe monad type *} |
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types 'a maybe = "one ++ 'a u" |
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constdefs |
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fail :: "'a maybe" |
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"fail \<equiv> sinl\<cdot>ONE" |
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return :: "'a \<rightarrow> 'a maybe" |
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"return \<equiv> sinr oo up" |
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lemma maybeE: |
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"\<lbrakk>p = \<bottom> \<Longrightarrow> Q; p = fail \<Longrightarrow> Q; \<And>x. p = return\<cdot>x \<Longrightarrow> Q\<rbrakk> \<Longrightarrow> Q" |
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apply (unfold fail_def return_def) |
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apply (rule_tac p=p in ssumE, simp) |
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apply (rule_tac p=x in oneE, simp, simp) |
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apply (rule_tac p=y in upE1, simp, simp) |
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done |
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subsection {* Monadic bind operator *} |
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constdefs |
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bind :: "'a maybe \<rightarrow> ('a \<rightarrow> 'b maybe) \<rightarrow> 'b maybe" |
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"bind \<equiv> \<Lambda> m f. sscase\<cdot>sinl\<cdot>(fup\<cdot>f)\<cdot>m" |
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syntax |
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"_bind" :: "'a maybe \<Rightarrow> ('a \<rightarrow> 'b maybe) \<Rightarrow> 'b maybe" |
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("(_ >>= _)" [50, 51] 50) |
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translations "m >>= k" == "bind\<cdot>m\<cdot>k" |
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nonterminals |
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maybebind maybebinds |
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syntax |
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"_MBIND" :: "pttrn \<Rightarrow> 'a maybe \<Rightarrow> maybebind" ("(2_ <-/ _)" 10) |
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"" :: "maybebind \<Rightarrow> maybebinds" ("_") |
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"_MBINDS" :: "[maybebind, maybebinds] \<Rightarrow> maybebinds" ("_;/ _") |
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"_MDO" :: "[maybebinds, 'a maybe] \<Rightarrow> 'a maybe" ("(do _;/ (_))" 10) |
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translations |
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"_MDO (_MBINDS b bs) e" == "_MDO b (_MDO bs e)" |
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"do (x,y) <- m; e" == "m >>= (LAM <x,y>. e)" |
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"do x <- m; e" == "m >>= (LAM x. e)" |
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text {* monad laws *} |
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lemma bind_strict [simp]: "UU >>= f = UU" |
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by (simp add: bind_def) |
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lemma bind_fail [simp]: "fail >>= f = fail" |
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by (simp add: bind_def fail_def) |
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lemma left_unit [simp]: "(return\<cdot>a) >>= k = k\<cdot>a" |
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by (simp add: bind_def return_def) |
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lemma right_unit [simp]: "m >>= return = m" |
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by (rule_tac p=m in maybeE, simp_all) |
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lemma bind_assoc [simp]: |
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"(do a <- m; b <- k\<cdot>a; h\<cdot>b) = (do b <- (do a <- m; k\<cdot>a); h\<cdot>b)" |
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by (rule_tac p=m in maybeE, simp_all) |
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subsection {* Run operator *} |
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constdefs |
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run:: "'a maybe \<rightarrow> 'a" |
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"run \<equiv> sscase\<cdot>\<bottom>\<cdot>(fup\<cdot>ID)" |
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text {* rewrite rules for run *} |
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lemma run_strict [simp]: "run\<cdot>\<bottom> = \<bottom>" |
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by (simp add: run_def) |
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lemma run_fail [simp]: "run\<cdot>fail = \<bottom>" |
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by (simp add: run_def fail_def) |
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lemma run_return [simp]: "run\<cdot>(return\<cdot>x) = x" |
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by (simp add: run_def return_def) |
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subsection {* Monad plus operator *} |
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constdefs |
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mplus :: "'a maybe \<rightarrow> 'a maybe \<rightarrow> 'a maybe" |
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"mplus \<equiv> \<Lambda> m1 m2. sscase\<cdot>(\<Lambda> x. m2)\<cdot>(fup\<cdot>return)\<cdot>m1" |
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syntax "+++" :: "'a maybe \<Rightarrow> 'a maybe \<Rightarrow> 'a maybe" (infixr 65) |
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translations "x +++ y" == "mplus\<cdot>x\<cdot>y" |
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text {* rewrite rules for mplus *} |
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lemma mplus_strict [simp]: "\<bottom> +++ m = \<bottom>" |
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by (simp add: mplus_def) |
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lemma mplus_fail [simp]: "fail +++ m = m" |
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by (simp add: mplus_def fail_def) |
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lemma mplus_return [simp]: "return\<cdot>x +++ m = return\<cdot>x" |
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by (simp add: mplus_def return_def) |
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lemma mplus_fail2 [simp]: "m +++ fail = m" |
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by (rule_tac p=m in maybeE, simp_all) |
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lemma mplus_assoc: "(x +++ y) +++ z = x +++ (y +++ z)" |
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by (rule_tac p=x in maybeE, simp_all) |
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subsection {* Match functions for built-in types *} |
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text {* Currently the package only supports lazy constructors *} |
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constdefs |
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match_cpair :: "'a \<times> 'b \<rightarrow> ('a \<times> 'b) maybe" |
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"match_cpair \<equiv> csplit\<cdot>(\<Lambda> x y. return\<cdot><x,y>)" |
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match_up :: "'a u \<rightarrow> 'a maybe" |
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"match_up \<equiv> fup\<cdot>return" |
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match_ONE :: "one \<rightarrow> unit maybe" |
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"match_ONE \<equiv> flift1 (\<lambda>u. return\<cdot>())" |
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match_TT :: "tr \<rightarrow> unit maybe" |
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"match_TT \<equiv> flift1 (\<lambda>b. if b then return\<cdot>() else fail)" |
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match_FF :: "tr \<rightarrow> unit maybe" |
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"match_FF \<equiv> flift1 (\<lambda>b. if b then fail else return\<cdot>())" |
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lemma match_cpair_simps [simp]: |
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"match_cpair\<cdot><x,y> = return\<cdot><x,y>" |
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by (simp add: match_cpair_def) |
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lemma match_up_simps [simp]: |
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"match_up\<cdot>(up\<cdot>x) = return\<cdot>x" |
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"match_up\<cdot>\<bottom> = \<bottom>" |
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by (simp_all add: match_up_def) |
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lemma match_ONE_simps [simp]: |
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"match_ONE\<cdot>ONE = return\<cdot>()" |
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"match_ONE\<cdot>\<bottom> = \<bottom>" |
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by (simp_all add: ONE_def match_ONE_def) |
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lemma match_TT_simps [simp]: |
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"match_TT\<cdot>TT = return\<cdot>()" |
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"match_TT\<cdot>FF = fail" |
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"match_TT\<cdot>\<bottom> = \<bottom>" |
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by (simp_all add: TT_def FF_def match_TT_def) |
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lemma match_FF_simps [simp]: |
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"match_FF\<cdot>FF = return\<cdot>()" |
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"match_FF\<cdot>TT = fail" |
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"match_FF\<cdot>\<bottom> = \<bottom>" |
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by (simp_all add: TT_def FF_def match_FF_def) |
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subsection {* Mutual recursion *} |
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text {* |
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The following rules are used to prove unfolding theorems from |
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fixed-point definitions of mutually recursive functions. |
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*} |
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lemma cpair_equalI: "\<lbrakk>x \<equiv> cfst\<cdot>p; y \<equiv> csnd\<cdot>p\<rbrakk> \<Longrightarrow> <x,y> \<equiv> p" |
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by (simp add: surjective_pairing_Cprod2) |
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lemma cpair_eqD1: "<x,y> = <x',y'> \<Longrightarrow> x = x'" |
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by simp |
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lemma cpair_eqD2: "<x,y> = <x',y'> \<Longrightarrow> y = y'" |
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by simp |
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text {* lemma for proving rewrite rules *} |
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lemma ssubst_lhs: "\<lbrakk>t = s; P s = Q\<rbrakk> \<Longrightarrow> P t = Q" |
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by simp |
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ML {* |
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val cpair_equalI = thm "cpair_equalI"; |
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val cpair_eqD1 = thm "cpair_eqD1"; |
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val cpair_eqD2 = thm "cpair_eqD2"; |
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val ssubst_lhs = thm "ssubst_lhs"; |
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*} |
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subsection {* Intitializing the fixrec package *} |
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use "fixrec_package.ML" |
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end |