src/HOL/Quickcheck_Examples/Quickcheck_Examples.thy

more documentation;

(*  Title:      HOL/Quickcheck_Examples/Quickcheck_Examples.thy
    Author:     Stefan Berghofer, Lukas Bulwahn
    Copyright   2004 - 2010 TU Muenchen
*)

section \<open>Examples for the 'quickcheck' command\<close>

theory Quickcheck_Examples
imports Complex_Main "HOL-Library.Dlist" "HOL-Library.DAList_Multiset"
begin

text \<open>
The 'quickcheck' command allows to find counterexamples by evaluating
formulae.
Currently, there are two different exploration schemes:
- random testing: this is incomplete, but explores the search space faster.
- exhaustive testing: this is complete, but increasing the depth leads to
  exponentially many assignments.

quickcheck can handle quantifiers on finite universes.

\<close>

declare [[quickcheck_timeout = 3600]]

subsection \<open>Lists\<close>

theorem "map g (map f xs) = map (g o f) xs"
  quickcheck[random, expect = no_counterexample]
  quickcheck[exhaustive, size = 3, expect = no_counterexample]
  oops

theorem "map g (map f xs) = map (f o g) xs"
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
  oops

theorem "rev (xs @ ys) = rev ys @ rev xs"
  quickcheck[random, expect = no_counterexample]
  quickcheck[exhaustive, expect = no_counterexample]
  quickcheck[exhaustive, size = 1000, timeout = 0.1]
  oops

theorem "rev (xs @ ys) = rev xs @ rev ys"
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
  oops

theorem "rev (rev xs) = xs"
  quickcheck[random, expect = no_counterexample]
  quickcheck[exhaustive, expect = no_counterexample]
  oops

theorem "rev xs = xs"
  quickcheck[tester = random, finite_types = true, report = false, expect = counterexample]
  quickcheck[tester = random, finite_types = false, report = false, expect = counterexample]
  quickcheck[tester = random, finite_types = true, report = true, expect = counterexample]
  quickcheck[tester = random, finite_types = false, report = true, expect = counterexample]
  quickcheck[tester = exhaustive, finite_types = true, expect = counterexample]
  quickcheck[tester = exhaustive, finite_types = false, expect = counterexample]
oops


text \<open>An example involving functions inside other data structures\<close>

primrec app :: "('a \<Rightarrow> 'a) list \<Rightarrow> 'a \<Rightarrow> 'a" where
  "app [] x = x"
  | "app (f # fs) x = app fs (f x)"

lemma "app (fs @ gs) x = app gs (app fs x)"
  quickcheck[random, expect = no_counterexample]
  quickcheck[exhaustive, size = 2, expect = no_counterexample]
  by (induct fs arbitrary: x) simp_all

lemma "app (fs @ gs) x = app fs (app gs x)"
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
  oops

primrec occurs :: "'a \<Rightarrow> 'a list \<Rightarrow> nat" where
  "occurs a [] = 0"
  | "occurs a (x#xs) = (if (x=a) then Suc(occurs a xs) else occurs a xs)"

primrec del1 :: "'a \<Rightarrow> 'a list \<Rightarrow> 'a list" where
  "del1 a [] = []"
  | "del1 a (x#xs) = (if (x=a) then xs else (x#del1 a xs))"

text \<open>A lemma, you'd think to be true from our experience with delAll\<close>
lemma "Suc (occurs a (del1 a xs)) = occurs a xs"
  \<comment> \<open>Wrong. Precondition needed.\<close>
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
  oops

lemma "xs ~= [] \<longrightarrow> Suc (occurs a (del1 a xs)) = occurs a xs"
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
    \<comment> \<open>Also wrong.\<close>
  oops

lemma "0 < occurs a xs \<longrightarrow> Suc (occurs a (del1 a xs)) = occurs a xs"
  quickcheck[random, expect = no_counterexample]
  quickcheck[exhaustive, expect = no_counterexample]
  by (induct xs) auto

primrec replace :: "'a \<Rightarrow> 'a \<Rightarrow> 'a list \<Rightarrow> 'a list" where
  "replace a b [] = []"
  | "replace a b (x#xs) = (if (x=a) then (b#(replace a b xs)) 
                            else (x#(replace a b xs)))"

lemma "occurs a xs = occurs b (replace a b xs)"
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
  \<comment> \<open>Wrong. Precondition needed.\<close>
  oops

lemma "occurs b xs = 0 \<or> a=b \<longrightarrow> occurs a xs = occurs b (replace a b xs)"
  quickcheck[random, expect = no_counterexample]
  quickcheck[exhaustive, expect = no_counterexample]
  by (induct xs) simp_all


subsection \<open>Trees\<close>

datatype 'a tree = Twig |  Leaf 'a | Branch "'a tree" "'a tree"

primrec leaves :: "'a tree \<Rightarrow> 'a list" where
  "leaves Twig = []"
  | "leaves (Leaf a) = [a]"
  | "leaves (Branch l r) = (leaves l) @ (leaves r)"

primrec plant :: "'a list \<Rightarrow> 'a tree" where
  "plant [] = Twig "
  | "plant (x#xs) = Branch (Leaf x) (plant xs)"

primrec mirror :: "'a tree \<Rightarrow> 'a tree" where
  "mirror (Twig) = Twig "
  | "mirror (Leaf a) = Leaf a "
  | "mirror (Branch l r) = Branch (mirror r) (mirror l)"

theorem "plant (rev (leaves xt)) = mirror xt"
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
    \<comment>\<open>Wrong!\<close> 
  oops

theorem "plant((leaves xt) @ (leaves yt)) = Branch xt yt"
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
    \<comment>\<open>Wrong!\<close> 
  oops

datatype 'a ntree = Tip "'a" | Node "'a" "'a ntree" "'a ntree"

primrec inOrder :: "'a ntree \<Rightarrow> 'a list" where
  "inOrder (Tip a)= [a]"
  | "inOrder (Node f x y) = (inOrder x)@[f]@(inOrder y)"

primrec root :: "'a ntree \<Rightarrow> 'a" where
  "root (Tip a) = a"
  | "root (Node f x y) = f"

theorem "hd (inOrder xt) = root xt"
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
  \<comment>\<open>Wrong!\<close> 
  oops


subsection \<open>Exhaustive Testing beats Random Testing\<close>

text \<open>Here are some examples from mutants from the List theory
where exhaustive testing beats random testing\<close>

lemma
  "[] ~= xs ==> hd xs = last (x # xs)"
quickcheck[random]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  assumes "!!i. [| i < n; i < length xs |] ==> P (xs ! i)" "n < length xs ==> ~ P (xs ! n)"
  shows "drop n xs = takeWhile P xs"
quickcheck[random, iterations = 10000, quiet]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "i < length (List.transpose (List.transpose xs)) ==> xs ! i = map (%xs. xs ! i) [ys<-xs. i < length ys]"
quickcheck[random, iterations = 10000]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "i < n - m ==> f (lcm m i) = map f [m..<n] ! i"
quickcheck[random, iterations = 10000, finite_types = false]
quickcheck[exhaustive, finite_types = false, expect = counterexample]
oops

lemma
  "i < n - m ==> f (lcm m i) = map f [m..<n] ! i"
quickcheck[random, iterations = 10000, finite_types = false]
quickcheck[exhaustive, finite_types = false, expect = counterexample]
oops

lemma
  "ns ! k < length ns ==> k <= sum_list ns"
quickcheck[random, iterations = 10000, finite_types = false, quiet]
quickcheck[exhaustive, finite_types = false, expect = counterexample]
oops

lemma
  "[| ys = x # xs1; zs = xs1 @ xs |] ==> ys @ zs = x # xs"
quickcheck[random, iterations = 10000]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
"i < length xs ==> take (Suc i) xs = [] @ xs ! i # take i xs"
quickcheck[random, iterations = 10000]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "i < length xs ==> take (Suc i) xs = (xs ! i # xs) @ take i []"
quickcheck[random, iterations = 10000]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "[| sorted (rev (map length xs)); i < length xs |] ==> xs ! i = map (%ys. ys ! i) [ys<-remdups xs. i < length ys]"
quickcheck[random]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "[| sorted (rev (map length xs)); i < length xs |] ==> xs ! i = map (%ys. ys ! i) [ys<-List.transpose xs. length ys \<in> {..<i}]"
quickcheck[random]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "(ys = zs) = (xs @ ys = splice xs zs)"
quickcheck[random]
quickcheck[exhaustive, expect = counterexample]
oops

subsection \<open>Random Testing beats Exhaustive Testing\<close>

lemma mult_inj_if_coprime_nat:
  "inj_on f A \<Longrightarrow> inj_on g B
   \<Longrightarrow> inj_on (%(a,b). f a * g b::nat) (A \<times> B)"
quickcheck[exhaustive]
quickcheck[random]
oops

subsection \<open>Examples with quantifiers\<close>

text \<open>
  These examples show that we can handle quantifiers.
\<close>

lemma "(\<exists>x. P x) \<longrightarrow> (\<forall>x. P x)"
  quickcheck[random, expect = counterexample]
  quickcheck[exhaustive, expect = counterexample]
oops

lemma "(\<forall>x. \<exists>y. P x y) \<longrightarrow> (\<exists>y. \<forall>x. P x y)"
  quickcheck[random, expect = counterexample]
  quickcheck[expect = counterexample]
oops

lemma "(\<exists>x. P x) \<longrightarrow> (\<exists>!x. P x)"
  quickcheck[random, expect = counterexample]
  quickcheck[expect = counterexample]
oops


subsection \<open>Examples with sets\<close>

lemma
  "{} = A Un - A"
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "[| bij_betw f A B; bij_betw f C D |] ==> bij_betw f (A Un C) (B Un D)"
quickcheck[exhaustive, expect = counterexample]
oops


subsection \<open>Examples with relations\<close>

lemma
  "acyclic (R :: ('a * 'a) set) ==> acyclic S ==> acyclic (R Un S)"
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "acyclic (R :: (nat * nat) set) ==> acyclic S ==> acyclic (R Un S)"
quickcheck[exhaustive, expect = counterexample]
oops

(* FIXME: some dramatic performance decrease after changing the code equation of the ntrancl *)
lemma
  "(x, z) : rtrancl (R Un S) ==> \<exists> y. (x, y) : rtrancl R & (y, z) : rtrancl S"
(*quickcheck[exhaustive, expect = counterexample]*)
oops

lemma
  "wf (R :: ('a * 'a) set) ==> wf S ==> wf (R Un S)"
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "wf (R :: (nat * nat) set) ==> wf S ==> wf (R Un S)"
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "wf (R :: (int * int) set) ==> wf S ==> wf (R Un S)"
quickcheck[exhaustive, expect = counterexample]
oops


subsection \<open>Examples with the descriptive operator\<close>

lemma
  "(THE x. x = a) = b"
quickcheck[random, expect = counterexample]
quickcheck[exhaustive, expect = counterexample]
oops

subsection \<open>Examples with Multisets\<close>

lemma
  "X + Y = Y + (Z :: 'a multiset)"
quickcheck[random, expect = counterexample]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "X - Y = Y - (Z :: 'a multiset)"
quickcheck[random, expect = counterexample]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "N + M - N = (N::'a multiset)"
quickcheck[random, expect = counterexample]
quickcheck[exhaustive, expect = counterexample]
oops

subsection \<open>Examples with numerical types\<close>

text \<open>
Quickcheck supports the common types nat, int, rat and real.
\<close>

lemma
  "(x :: nat) > 0 ==> y > 0 ==> z > 0 ==> x * x + y * y \<noteq> z * z"
quickcheck[exhaustive, size = 10, expect = counterexample]
quickcheck[random, size = 10]
oops

lemma
  "(x :: int) > 0 ==> y > 0 ==> z > 0 ==> x * x + y * y \<noteq> z * z"
quickcheck[exhaustive, size = 10, expect = counterexample]
quickcheck[random, size = 10]
oops

lemma
  "(x :: rat) > 0 ==> y > 0 ==> z > 0 ==> x * x + y * y \<noteq> z * z"
quickcheck[exhaustive, size = 10, expect = counterexample]
quickcheck[random, size = 10]
oops

lemma "(x :: rat) >= 0"
quickcheck[random, expect = counterexample]
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "(x :: real) > 0 ==> y > 0 ==> z > 0 ==> x * x + y * y \<noteq> z * z"
quickcheck[exhaustive, size = 10, expect = counterexample]
quickcheck[random, size = 10]
oops

lemma "(x :: real) >= 0"
quickcheck[random, expect = counterexample]
quickcheck[exhaustive, expect = counterexample]
oops

subsubsection \<open>floor and ceiling functions\<close>

lemma "\<lfloor>x\<rfloor> + \<lfloor>y\<rfloor> = \<lfloor>x + y :: rat\<rfloor>"
quickcheck[expect = counterexample]
oops

lemma "\<lfloor>x\<rfloor> + \<lfloor>y\<rfloor> = \<lfloor>x + y :: real\<rfloor>"
quickcheck[expect = counterexample]
oops

lemma "\<lceil>x\<rceil> + \<lceil>y\<rceil> = \<lceil>x + y :: rat\<rceil>"
quickcheck[expect = counterexample]
oops

lemma "\<lceil>x\<rceil> + \<lceil>y\<rceil> = \<lceil>x + y :: real\<rceil>"
quickcheck[expect = counterexample]
oops

subsection \<open>Examples with abstract types\<close>

lemma
  "Dlist.length (Dlist.remove x xs) = Dlist.length xs - 1"
quickcheck[exhaustive]
quickcheck[random]
oops

lemma
  "Dlist.length (Dlist.insert x xs) = Dlist.length xs + 1"
quickcheck[exhaustive]
quickcheck[random]
oops

subsection \<open>Examples with Records\<close>

record point =
  xpos :: nat
  ypos :: nat

lemma
  "xpos r = xpos r' ==> r = r'"
quickcheck[exhaustive, expect = counterexample]
quickcheck[random, expect = counterexample]
oops

datatype colour = Red | Green | Blue

record cpoint = point +
  colour :: colour

lemma
  "xpos r = xpos r' ==> ypos r = ypos r' ==> (r :: cpoint) = r'"
quickcheck[exhaustive, expect = counterexample]
quickcheck[random, expect = counterexample]
oops

subsection \<open>Examples with locales\<close>

locale Truth

context Truth
begin

lemma "False"
quickcheck[exhaustive, expect = counterexample]
oops

end

interpretation Truth .

context Truth
begin

lemma "False"
quickcheck[exhaustive, expect = counterexample]
oops

end

locale antisym =
  fixes R
  assumes "R x y --> R y x --> x = y"

interpretation equal : antisym "op =" by standard simp
interpretation order_nat : antisym "op <= :: nat => _ => _" by standard simp

lemma (in antisym)
  "R x y --> R y z --> R x z"
quickcheck[exhaustive, finite_type_size = 2, expect = no_counterexample]
quickcheck[exhaustive, expect = counterexample]
oops

declare [[quickcheck_locale = "interpret"]]

lemma (in antisym)
  "R x y --> R y z --> R x z"
quickcheck[exhaustive, expect = no_counterexample]
oops

declare [[quickcheck_locale = "expand"]]

lemma (in antisym)
  "R x y --> R y z --> R x z"
quickcheck[exhaustive, finite_type_size = 2, expect = no_counterexample]
quickcheck[exhaustive, expect = counterexample]
oops


subsection \<open>Examples with HOL quantifiers\<close>

lemma
  "\<forall> xs ys. xs = [] --> xs = ys"
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "ys = [] --> (\<forall>xs. xs = [] --> xs = y # ys)"
quickcheck[exhaustive, expect = counterexample]
oops

lemma
  "\<forall>xs. (\<exists> ys. ys = []) --> xs = ys"
quickcheck[exhaustive, expect = counterexample]
oops

subsection \<open>Examples with underspecified/partial functions\<close>

lemma
  "xs = [] ==> hd xs \<noteq> x"
quickcheck[exhaustive, expect = no_counterexample]
quickcheck[random, report = false, expect = no_counterexample]
quickcheck[random, report = true, expect = no_counterexample]
oops

lemma
  "xs = [] ==> hd xs = x"
quickcheck[exhaustive, expect = no_counterexample]
quickcheck[random, report = false, expect = no_counterexample]
quickcheck[random, report = true, expect = no_counterexample]
oops

lemma "xs = [] ==> hd xs = x ==> x = y"
quickcheck[exhaustive, expect = no_counterexample]
quickcheck[random, report = false, expect = no_counterexample]
quickcheck[random, report = true, expect = no_counterexample]
oops

text \<open>with the simple testing scheme\<close>

setup Exhaustive_Generators.setup_exhaustive_datatype_interpretation
declare [[quickcheck_full_support = false]]

lemma
  "xs = [] ==> hd xs \<noteq> x"
quickcheck[exhaustive, expect = no_counterexample]
oops

lemma
  "xs = [] ==> hd xs = x"
quickcheck[exhaustive, expect = no_counterexample]
oops

lemma "xs = [] ==> hd xs = x ==> x = y"
quickcheck[exhaustive, expect = no_counterexample]
oops

declare [[quickcheck_full_support = true]]


subsection \<open>Equality Optimisation\<close>

lemma
  "f x = y ==> y = (0 :: nat)"
quickcheck
oops

lemma
  "y = f x ==> y = (0 :: nat)"
quickcheck
oops

lemma
  "f y = zz # zzs ==> zz = (0 :: nat) \<and> zzs = []"
quickcheck
oops

lemma
  "f y = x # x' # xs ==> x = (0 :: nat) \<and> x' = 0 \<and> xs = []"
quickcheck
oops

lemma
  "x = f x \<Longrightarrow> x = (0 :: nat)"
quickcheck
oops

lemma
  "f y = x # x # xs ==> x = (0 :: nat) \<and> xs = []"
quickcheck
oops

lemma
  "m1 k = Some v \<Longrightarrow> (m1 ++ m2) k = Some v"
quickcheck
oops


end