theory Chap03

imports Main

begin

lemma "\<lbrakk> xs @ zs = ys @ xs; [] @ xs = [] @ [] \<rbrakk> \<Longrightarrow> ys = zs"

apply simp

done

lemma "\<forall> x. f x = g (f (g x)) \<Longrightarrow> f [] = f [] @ []"

apply (simp (no_asm))

done

definition xor :: "bool \<Rightarrow> bool \<Rightarrow> bool" where

"xor A B \<equiv> (A \<and> \<not>B) \<or> (\<not>A \<and> B)"

lemma "xor A (\<not>A)"

apply(simp only: xor_def)

apply(simp add: xor_def)

done

lemma "(let xs = [] in xs@ys@xs) = ys"

apply(simp only: Let_def)

apply(simp add: Let_def)

done

(* 3.1.8 Conditioal Simplification Rules  *)

lemma hd_Cons_tl: "xs \<noteq> [] \<Longrightarrow> hd xs # tl xs = xs"

using [[simp_trace=true]]

apply(case_tac xs)

apply(simp)

apply(simp)

done

lemma "xs \<noteq> [] \<Longrightarrow> hd(rev xs) # tl(rev xs) = rev xs"

apply(case_tac xs)

using [[simp_trace=true]]

apply(simp)

apply(simp)

done

(* 3.1.9 Automatic Case Splits  *)

lemma "\<forall> xs. if xs = [] then rev xs = [] else rev xs \<noteq> []"

apply(split split_if)

apply(simp)

done

lemma "(case xs of [] \<Rightarrow> zs | y#ys \<Rightarrow> y#(ys@zs)) = xs@zs"

apply(split list.split)

apply(simp split: list.split)

done

lemma "if xs = [] then ys \<noteq> [] else ys = [] \<Longrightarrow> xs @ ys \<noteq> []"

apply(split split_if_asm)

apply(simp)

apply(auto)

done

(* 3.2 Induction Heuristics  *)

primrec itrev :: "'a list \<Rightarrow> 'a list \<Rightarrow> 'a list" where

"itrev [] ys = ys" |

"itrev (x#xs) ys = itrev xs (x#ys)"

lemma "itrev xs [] = rev xs"

apply(induct_tac xs)

apply(simp)

apply(auto)

oops

lemma "itrev xs ys = rev xs @ ys"

apply(induct_tac xs)

apply(simp_all)

oops

lemma "\<forall> ys. itrev xs ys = rev xs @ ys"

apply(induct_tac xs)

apply(simp)

apply(simp)

done

primrec add1 :: "nat \<Rightarrow> nat \<Rightarrow> nat" where

"add1 m 0 = m" |

"add1 m (Suc n) = add1 (Suc m) n"

value "add1 1 3"

value "1 + 3"

lemma abc [simp]: "add1 m 0 = m"

apply(induction m)

apply(simp)

apply(simp)

done

lemma abc2 "add1 m n = m+n"

apply(induction n)

apply(auto)

oops

(* 3.3 Case Study: Compiling Expressions  *)

type_synonym 'v binop = "'v \<Rightarrow> 'v \<Rightarrow> 'v"

datatype ('a, 'v)expr = 

  Cex 'v

| Vex 'a

| Bex "'v binop" "('a,'v)expr" "('a,'v)expr"

primrec "value" :: "('a,'v)expr \<Rightarrow> ('a \<Rightarrow> 'v) \<Rightarrow> 'v" where

"value (Cex v) env = v" |

"value (Vex a) env = env a" |

"value (Bex f e1 e2) env = f (value e1 env) (value e2 env)"

datatype ('a,'v)instr = 

  Const 'v

| Load 'a

| Apply "'v binop"

primrec exec :: "('a,'v)instr list \<Rightarrow> ('a\<Rightarrow>'v) \<Rightarrow> 'v list \<Rightarrow> 'v list" where

"exec [] s vs = vs" |

"exec (i#is) s vs = (case i of

    Const v \<Rightarrow> exec is s (v#vs)

  | Load a \<Rightarrow> exec is s ((s a)#vs)

  | Apply f \<Rightarrow> exec is s ((f (hd vs) (hd(tl vs)))#(tl(tl vs))))"

primrec compile :: "('a,'v)expr \<Rightarrow> ('a,'v)instr list" where

"compile (Cex v) = [Const v]" |

"compile (Vex a) = [Load a]" |

"compile (Bex f e1 e2) = (compile e2) @ (compile e1) @ [Apply f]"

theorem "exec (compile e) s [] = [value e s]"

(*the theorem needs to be generalized*)

oops

(*more generalized theorem*)

theorem "\<forall> vs. exec (compile e) s vs = (value e s) # vs"

apply(induct_tac e)

apply(simp)

apply(simp)

oops

lemma exec_app[simp]: "\<forall> vs. exec (xs@ys) s vs = exec ys s (exec xs s vs)"

apply(induct_tac xs)

apply(simp)

apply(simp)

apply(simp split: instr.split)

done

(* 2.5.6 Case Study: Boolean Expressions *)

datatype boolex = Const bool | Var nat | Neg boolex

| And boolex boolex

primrec "value2" :: "boolex \<Rightarrow> (nat \<Rightarrow> bool) \<Rightarrow> bool" where

"value2 (Const b)  env = b" |

"value2 (Var x)    env = env x" |

"value2 (Neg b)    env = (\<not> value2 b env)" |

"value2 (And b c)  env = (value2 b env \<and> value2 c env)"

value "Const true"

value "Suc(Suc(0))"

'b::Const = "true"

value "value2 (Const true) (env = true)"