theory Matcher2
  imports "Main" 
begin

section {* Regular Expressions *}

datatype rexp =
  NULL
| EMPTY
| CHAR char
| SEQ rexp rexp
| ALT rexp rexp
| STAR rexp
| NOT rexp
| PLUS rexp
| OPT rexp
| NTIMES rexp nat
| NMTIMES rexp nat nat

fun M :: "rexp \<Rightarrow> nat"
where
  "M (NULL) = 0"
| "M (EMPTY) = 0"
| "M (CHAR char) = 0"
| "M (SEQ r1 r2) = Suc ((M r1) + (M r2))"
| "M (ALT r1 r2) = Suc ((M r1) + (M r2))"
| "M (STAR r) = Suc (M r)"
| "M (NOT r) = Suc (M r)"
| "M (PLUS r) = Suc (M r)"
| "M (OPT r) = Suc (M r)"
| "M (NTIMES r n) = Suc (M r) * 2 * (Suc n)"
| "M (NMTIMES r n m) = Suc (M r) * 2 * (Suc n + Suc m)"

section {* Sequential Composition of Sets *}

definition
  Seq :: "string set \<Rightarrow> string set \<Rightarrow> string set" ("_ ;; _" [100,100] 100)
where 
  "A ;; B = {s1 @ s2 | s1 s2. s1 \<in> A \<and> s2 \<in> B}"

text {* Two Simple Properties about Sequential Composition *}

lemma seq_empty [simp]:
  shows "A ;; {[]} = A"
  and   "{[]} ;; A = A"
by (simp_all add: Seq_def)

lemma seq_null [simp]:
  shows "A ;; {} = {}"
  and   "{} ;; A = {}"
by (simp_all add: Seq_def)

lemma seq_union:
  shows "A ;; (B \<union> C) = A ;; B \<union> A ;; C"
  and   "(B \<union> C) ;; A = B ;; A \<union> C ;; A"
by (auto simp add: Seq_def)

lemma seq_Union:
  shows "A ;; (\<Union>x\<in>B. C x) = (\<Union>x\<in>B. A ;; C x)"
by (auto simp add: Seq_def)

lemma seq_empty_in [simp]:
  "[] \<in> A ;; B \<longleftrightarrow> ([] \<in> A \<and> [] \<in> B)"
by (simp add: Seq_def)

lemma seq_assoc: 
  shows "A ;; (B ;; C) = (A ;; B) ;; C" 
apply(auto simp add: Seq_def)
apply(metis append_assoc)
apply(metis)
done


section {* Power for Sets *}

fun 
  pow :: "string set \<Rightarrow> nat \<Rightarrow> string set" ("_ \<up> _" [101, 102] 101)
where
   "A \<up> 0 = {[]}"
|  "A \<up> (Suc n) = A ;; (A \<up> n)"

lemma pow_empty [simp]:
  shows "[] \<in> A \<up> n \<longleftrightarrow> (n = 0 \<or> [] \<in> A)"
by (induct n) (auto)

lemma pow_plus:
  "A \<up> (n + m) = A \<up> n ;; A \<up> m"
by (induct n) (simp_all add: seq_assoc)

section {* Kleene Star for Sets *}

inductive_set
  Star :: "string set \<Rightarrow> string set" ("_\<star>" [101] 102)
  for A :: "string set"
where
  start[intro]: "[] \<in> A\<star>"
| step[intro]:  "\<lbrakk>s1 \<in> A; s2 \<in> A\<star>\<rbrakk> \<Longrightarrow> s1 @ s2 \<in> A\<star>"

text {* A Standard Property of Star *}

lemma star_decomp: 
  assumes a: "c # x \<in> A\<star>" 
  shows "\<exists>a b. x = a @ b \<and> c # a \<in> A \<and> b \<in> A\<star>"
using a 
using a
by (induct x\<equiv>"c # x" rule: Star.induct) 
   (auto simp add: append_eq_Cons_conv)

lemma star_cases:
  shows "A\<star> = {[]} \<union> A ;; A\<star>"
unfolding Seq_def 
by (auto) (metis Star.simps)

lemma Star_in_Pow:
  assumes a: "s \<in> A\<star>"
  shows "\<exists>n. s \<in> A \<up> n"
using a
apply(induct)
apply(auto)
apply(rule_tac x="Suc n" in exI)
apply(auto simp add: Seq_def)
done

lemma Pow_in_Star:
  assumes a: "s \<in> A \<up> n"
  shows "s \<in> A\<star>"
using a
by (induct n arbitrary: s) (auto simp add: Seq_def)


lemma Star_def2: 
  shows "A\<star> = (\<Union>n. A \<up> n)"
using Star_in_Pow Pow_in_Star
by (auto)



section {* Semantics of Regular Expressions *}
 
fun
  L :: "rexp \<Rightarrow> string set"
where
  "L (NULL) = {}"
| "L (EMPTY) = {[]}"
| "L (CHAR c) = {[c]}"
| "L (SEQ r1 r2) = (L r1) ;; (L r2)"
| "L (ALT r1 r2) = (L r1) \<union> (L r2)"
| "L (STAR r) = (L r)\<star>"
| "L (NOT r) = UNIV - (L r)"
| "L (PLUS r) = (L r) ;; ((L r)\<star>)"
| "L (OPT r) = (L r) \<union> {[]}"
| "L (NTIMES r n) = (L r) \<up> n"
| "L (NMTIMES r n m) = (\<Union>i\<in> {n..n+m} . ((L r) \<up> i))" 


section {* The Matcher *}

fun
 nullable :: "rexp \<Rightarrow> bool"
where
  "nullable (NULL) = False"
| "nullable (EMPTY) = True"
| "nullable (CHAR c) = False"
| "nullable (ALT r1 r2) = (nullable r1 \<or> nullable r2)"
| "nullable (SEQ r1 r2) = (nullable r1 \<and> nullable r2)"
| "nullable (STAR r) = True"
| "nullable (NOT r) = (\<not>(nullable r))"
| "nullable (PLUS r) = (nullable r)"
| "nullable (OPT r) = True"
| "nullable (NTIMES r n) = (if n = 0 then True else nullable r)"
| "nullable (NMTIMES r n m) = (if n = 0 then True else nullable r)"

function
 der :: "char \<Rightarrow> rexp \<Rightarrow> rexp"
where
  "der c (NULL) = NULL"
| "der c (EMPTY) = NULL"
| "der c (CHAR d) = (if c = d then EMPTY else NULL)"
| "der c (ALT r1 r2) = ALT (der c r1) (der c r2)"
| "der c (SEQ r1 r2) = ALT (SEQ (der c r1) r2) (if nullable r1 then der c r2 else NULL)"
| "der c (STAR r) = SEQ (der c r) (STAR r)"
| "der c (NOT r) = NOT(der c r)"
| "der c (PLUS r) = SEQ (der c r) (STAR r)"
| "der c (OPT r) = der c r"
| "der c (NTIMES r 0) = NULL"
| "der c (NTIMES r (Suc n)) = der c (SEQ r (NTIMES r n))"
| "der c (NMTIMES r 0 0) = NULL"
| "der c (NMTIMES r 0 (Suc m)) = ALT (der c (NTIMES r (Suc m))) (der c (NMTIMES r 0 m))"
| "der c (NMTIMES r (Suc n) m) = der c  (SEQ r (NMTIMES r n m))"
by pat_completeness auto

termination der 
by (relation "measure (\<lambda>(c, r). M r)") (simp_all)


fun 
 ders :: "string \<Rightarrow> rexp \<Rightarrow> rexp"
where
  "ders [] r = r"
| "ders (c # s) r = ders s (der c r)"

fun
  matcher :: "rexp \<Rightarrow> string \<Rightarrow> bool"
where
  "matcher r s = nullable (ders s r)"


section {* Correctness Proof of the Matcher *}

lemma nullable_correctness:
  shows "nullable r  \<longleftrightarrow> [] \<in> (L r)"
by(induct r) (auto simp add: Seq_def) 


section {* Left-Quotient of a Set *}

definition
  Der :: "char \<Rightarrow> string set \<Rightarrow> string set"
where
  "Der c A \<equiv> {s. [c] @ s \<in> A}"

lemma Der_null [simp]:
  shows "Der c {} = {}"
unfolding Der_def
by auto

lemma Der_empty [simp]:
  shows "Der c {[]} = {}"
unfolding Der_def
by auto

lemma Der_char [simp]:
  shows "Der c {[d]} = (if c = d then {[]} else {})"
unfolding Der_def
by auto

lemma Der_union [simp]:
  shows "Der c (A \<union> B) = Der c A \<union> Der c B"
unfolding Der_def
by auto

lemma Der_insert_nil [simp]:
  shows "Der c (insert [] A) = Der c A"
unfolding Der_def 
by auto 

lemma Der_seq [simp]:
  shows "Der c (A ;; B) = (Der c A) ;; B \<union> (if [] \<in> A then Der c B else {})"
unfolding Der_def Seq_def
by (auto simp add: Cons_eq_append_conv)

lemma Der_star [simp]:
  shows "Der c (A\<star>) = (Der c A) ;; A\<star>"
proof -    
  have "Der c (A\<star>) = Der c ({[]} \<union> A ;; A\<star>)"
    by (simp only: star_cases[symmetric])
  also have "... = Der c (A ;; A\<star>)"
    by (simp only: Der_union Der_empty) (simp)
  also have "... = (Der c A) ;; A\<star> \<union> (if [] \<in> A then Der c (A\<star>) else {})"
    by simp
  also have "... =  (Der c A) ;; A\<star>"
    unfolding Seq_def Der_def
    by (auto dest: star_decomp)
  finally show "Der c (A\<star>) = (Der c A) ;; A\<star>" .
qed

lemma Der_UNIV [simp]:
  "Der c (UNIV - A) = UNIV - Der c A"
unfolding Der_def
by (auto)

lemma Der_pow [simp]:
  shows "Der c (A \<up> (Suc n)) = (Der c A) ;; (A \<up> n) \<union> (if [] \<in> A then Der c (A \<up> n) else {})"
unfolding Der_def 
by(auto simp add: Cons_eq_append_conv Seq_def)

lemma Der_UNION [simp]: 
  shows "Der c (\<Union>x\<in>A. B x) = (\<Union>x\<in>A. Der c (B x))"
by (auto simp add: Der_def)

lemma Suc_Union:
  "(\<Union> x\<le>Suc m. B x) = (B (Suc m) \<union> (\<Union> x\<le>m. B x))"
by (metis UN_insert atMost_Suc)

lemma Suc_reduce_Union:
  "(\<Union>x\<in>{Suc n..Suc m}. B x) = (\<Union>x\<in>{n..m}. B (Suc x))"
by (metis UN_extend_simps(10) image_Suc_atLeastAtMost)


lemma der_correctness:
  shows "L (der c r) = Der c (L r)"
by (induct rule: der.induct) 
   (simp_all add: nullable_correctness 
    Suc_Union Suc_reduce_Union seq_Union atLeast0AtMost)


lemma matcher_correctness:
  shows "matcher r s \<longleftrightarrow> s \<in> L r"
by (induct s arbitrary: r)
   (simp_all add: nullable_correctness der_correctness Der_def)


end