1 (* Title: HOL/BNF/Examples/Stream.thy
2 Author: Dmitriy Traytel, TU Muenchen
3 Author: Andrei Popescu, TU Muenchen
9 header {* Infinite Streams *}
15 codatatype (sset: 'a) stream (map: smap rel: stream_all2) =
16 Stream (shd: 'a) (stl: "'a stream") (infixr "##" 65)
20 lemma stream_case_cert:
21 assumes "CASE \<equiv> case_stream c"
22 shows "CASE (a ## s) \<equiv> c a s"
23 using assms by simp_all
26 Code.add_case @{thm stream_case_cert}
29 (*for code generation only*)
30 definition smember :: "'a \<Rightarrow> 'a stream \<Rightarrow> bool" where
31 [code_abbrev]: "smember x s \<longleftrightarrow> x \<in> sset s"
33 lemma smember_code[code, simp]: "smember x (Stream y s) = (if x = y then True else smember x s)"
34 unfolding smember_def by auto
36 hide_const (open) smember
38 (* TODO: Provide by the package*)
40 "\<lbrakk>\<And>s. P (shd s) s; \<And>s y. \<lbrakk>y \<in> sset (stl s); P y (stl s)\<rbrakk> \<Longrightarrow> P y s\<rbrakk> \<Longrightarrow>
41 \<forall>y \<in> sset s. P y s"
42 apply (rule stream.dtor_set_induct)
43 apply (auto simp add: shd_def stl_def fsts_def snds_def split_beta)
44 apply (metis Stream_def fst_conv stream.case stream.dtor_ctor stream.exhaust)
45 by (metis Stream_def sndI stl_def stream.collapse stream.dtor_ctor)
47 lemma smap_simps[simp]:
48 "shd (smap f s) = f (shd s)" "stl (smap f s) = smap f (stl s)"
49 by (case_tac [!] s) auto
51 theorem shd_sset: "shd s \<in> sset s"
54 theorem stl_sset: "y \<in> sset (stl s) \<Longrightarrow> y \<in> sset s"
57 (* only for the non-mutual case: *)
58 theorem sset_induct1[consumes 1, case_names shd stl, induct set: "sset"]:
59 assumes "y \<in> sset s" and "\<And>s. P (shd s) s"
60 and "\<And>s y. \<lbrakk>y \<in> sset (stl s); P y (stl s)\<rbrakk> \<Longrightarrow> P y s"
62 using assms sset_induct by blast
66 subsection {* prepend list to stream *}
68 primrec shift :: "'a list \<Rightarrow> 'a stream \<Rightarrow> 'a stream" (infixr "@-" 65) where
70 | "shift (x # xs) s = x ## shift xs s"
72 lemma smap_shift[simp]: "smap f (xs @- s) = map f xs @- smap f s"
75 lemma shift_append[simp]: "(xs @ ys) @- s = xs @- ys @- s"
78 lemma shift_simps[simp]:
79 "shd (xs @- s) = (if xs = [] then shd s else hd xs)"
80 "stl (xs @- s) = (if xs = [] then stl s else tl xs @- s)"
83 lemma sset_shift[simp]: "sset (xs @- s) = set xs \<union> sset s"
86 lemma shift_left_inj[simp]: "xs @- s1 = xs @- s2 \<longleftrightarrow> s1 = s2"
90 subsection {* set of streams with elements in some fixed set *}
93 streams :: "'a set \<Rightarrow> 'a stream set"
96 Stream[intro!, simp, no_atp]: "\<lbrakk>a \<in> A; s \<in> streams A\<rbrakk> \<Longrightarrow> a ## s \<in> streams A"
98 lemma shift_streams: "\<lbrakk>w \<in> lists A; s \<in> streams A\<rbrakk> \<Longrightarrow> w @- s \<in> streams A"
101 lemma streams_Stream: "x ## s \<in> streams A \<longleftrightarrow> x \<in> A \<and> s \<in> streams A"
102 by (auto elim: streams.cases)
104 lemma streams_stl: "s \<in> streams A \<Longrightarrow> stl s \<in> streams A"
105 by (cases s) (auto simp: streams_Stream)
107 lemma streams_shd: "s \<in> streams A \<Longrightarrow> shd s \<in> A"
108 by (cases s) (auto simp: streams_Stream)
111 assumes "sset s \<subseteq> A"
112 shows "s \<in> streams A"
113 using assms proof (coinduction arbitrary: s)
114 case streams then show ?case by (cases s) simp
118 assumes "s \<in> streams A"
119 shows "sset s \<subseteq> A"
121 fix x assume "x \<in> sset s" from this `s \<in> streams A` show "x \<in> A"
122 by (induct s) (auto intro: streams_shd streams_stl)
125 lemma streams_iff_sset: "s \<in> streams A \<longleftrightarrow> sset s \<subseteq> A"
126 by (metis sset_streams streams_sset)
128 lemma streams_mono: "s \<in> streams A \<Longrightarrow> A \<subseteq> B \<Longrightarrow> s \<in> streams B"
129 unfolding streams_iff_sset by auto
131 lemma smap_streams: "s \<in> streams A \<Longrightarrow> (\<And>x. x \<in> A \<Longrightarrow> f x \<in> B) \<Longrightarrow> smap f s \<in> streams B"
132 unfolding streams_iff_sset stream.set_map by auto
134 lemma streams_empty: "streams {} = {}"
135 by (auto elim: streams.cases)
137 lemma streams_UNIV[simp]: "streams UNIV = UNIV"
138 by (auto simp: streams_iff_sset)
140 subsection {* nth, take, drop for streams *}
142 primrec snth :: "'a stream \<Rightarrow> nat \<Rightarrow> 'a" (infixl "!!" 100) where
144 | "s !! Suc n = stl s !! n"
146 lemma snth_smap[simp]: "smap f s !! n = f (s !! n)"
147 by (induct n arbitrary: s) auto
149 lemma shift_snth_less[simp]: "p < length xs \<Longrightarrow> (xs @- s) !! p = xs ! p"
150 by (induct p arbitrary: xs) (auto simp: hd_conv_nth nth_tl)
152 lemma shift_snth_ge[simp]: "p \<ge> length xs \<Longrightarrow> (xs @- s) !! p = s !! (p - length xs)"
153 by (induct p arbitrary: xs) (auto simp: Suc_diff_eq_diff_pred)
155 lemma snth_sset[simp]: "s !! n \<in> sset s"
156 by (induct n arbitrary: s) (auto intro: shd_sset stl_sset)
158 lemma sset_range: "sset s = range (snth s)"
159 proof (intro equalityI subsetI)
160 fix x assume "x \<in> sset s"
161 thus "x \<in> range (snth s)"
164 then obtain n where "x = stl s !! n" by auto
165 thus ?case by (auto intro: range_eqI[of _ _ "Suc n"])
166 qed (auto intro: range_eqI[of _ _ 0])
169 primrec stake :: "nat \<Rightarrow> 'a stream \<Rightarrow> 'a list" where
171 | "stake (Suc n) s = shd s # stake n (stl s)"
173 lemma length_stake[simp]: "length (stake n s) = n"
174 by (induct n arbitrary: s) auto
176 lemma stake_smap[simp]: "stake n (smap f s) = map f (stake n s)"
177 by (induct n arbitrary: s) auto
179 primrec sdrop :: "nat \<Rightarrow> 'a stream \<Rightarrow> 'a stream" where
181 | "sdrop (Suc n) s = sdrop n (stl s)"
183 lemma sdrop_simps[simp]:
184 "shd (sdrop n s) = s !! n" "stl (sdrop n s) = sdrop (Suc n) s"
185 by (induct n arbitrary: s) auto
187 lemma sdrop_smap[simp]: "sdrop n (smap f s) = smap f (sdrop n s)"
188 by (induct n arbitrary: s) auto
190 lemma sdrop_stl: "sdrop n (stl s) = stl (sdrop n s)"
193 lemma stake_sdrop: "stake n s @- sdrop n s = s"
194 by (induct n arbitrary: s) auto
196 lemma id_stake_snth_sdrop:
197 "s = stake i s @- s !! i ## sdrop (Suc i) s"
198 by (subst stake_sdrop[symmetric, of _ i]) (metis sdrop_simps stream.collapse)
200 lemma smap_alt: "smap f s = s' \<longleftrightarrow> (\<forall>n. f (s !! n) = s' !! n)" (is "?L = ?R")
203 then have "\<And>n. smap f (sdrop n s) = sdrop n s'"
204 by coinduction (auto intro: exI[of _ 0] simp del: sdrop.simps(2))
205 then show ?L using sdrop.simps(1) by metis
208 lemma stake_invert_Nil[iff]: "stake n s = [] \<longleftrightarrow> n = 0"
211 lemma sdrop_shift: "\<lbrakk>s = w @- s'; length w = n\<rbrakk> \<Longrightarrow> sdrop n s = s'"
212 by (induct n arbitrary: w s) auto
214 lemma stake_shift: "\<lbrakk>s = w @- s'; length w = n\<rbrakk> \<Longrightarrow> stake n s = w"
215 by (induct n arbitrary: w s) auto
217 lemma stake_add[simp]: "stake m s @ stake n (sdrop m s) = stake (m + n) s"
218 by (induct m arbitrary: s) auto
220 lemma sdrop_add[simp]: "sdrop n (sdrop m s) = sdrop (m + n) s"
221 by (induct m arbitrary: s) auto
223 partial_function (tailrec) sdrop_while :: "('a \<Rightarrow> bool) \<Rightarrow> 'a stream \<Rightarrow> 'a stream" where
224 "sdrop_while P s = (if P (shd s) then sdrop_while P (stl s) else s)"
226 lemma sdrop_while_Stream[code]:
227 "sdrop_while P (Stream a s) = (if P a then sdrop_while P s else Stream a s)"
228 by (subst sdrop_while.simps) simp
230 lemma sdrop_while_sdrop_LEAST:
231 assumes "\<exists>n. P (s !! n)"
232 shows "sdrop_while (Not o P) s = sdrop (LEAST n. P (s !! n)) s"
234 from assms obtain m where "P (s !! m)" "\<And>n. P (s !! n) \<Longrightarrow> m \<le> n"
235 and *: "(LEAST n. P (s !! n)) = m" by atomize_elim (auto intro: LeastI Least_le)
236 thus ?thesis unfolding *
237 proof (induct m arbitrary: s)
239 hence "sdrop_while (Not \<circ> P) (stl s) = sdrop m (stl s)"
240 by (metis (full_types) not_less_eq_eq snth.simps(2))
241 moreover from Suc(3) have "\<not> (P (s !! 0))" by blast
242 ultimately show ?case by (subst sdrop_while.simps) simp
243 qed (metis comp_apply sdrop.simps(1) sdrop_while.simps snth.simps(1))
246 primcorec sfilter where
247 "shd (sfilter P s) = shd (sdrop_while (Not o P) s)"
248 | "stl (sfilter P s) = sfilter P (stl (sdrop_while (Not o P) s))"
250 lemma sfilter_Stream: "sfilter P (x ## s) = (if P x then x ## sfilter P s else sfilter P s)"
252 case True thus ?thesis by (subst sfilter.ctr) (simp add: sdrop_while_Stream)
254 case False thus ?thesis by (subst (1 2) sfilter.ctr) (simp add: sdrop_while_Stream)
258 subsection {* unary predicates lifted to streams *}
260 definition "stream_all P s = (\<forall>p. P (s !! p))"
262 lemma stream_all_iff[iff]: "stream_all P s \<longleftrightarrow> Ball (sset s) P"
263 unfolding stream_all_def sset_range by auto
265 lemma stream_all_shift[simp]: "stream_all P (xs @- s) = (list_all P xs \<and> stream_all P s)"
266 unfolding stream_all_iff list_all_iff by auto
268 lemma stream_all_Stream: "stream_all P (x ## X) \<longleftrightarrow> P x \<and> stream_all P X"
272 subsection {* recurring stream out of a list *}
274 primcorec cycle :: "'a list \<Rightarrow> 'a stream" where
275 "shd (cycle xs) = hd xs"
276 | "stl (cycle xs) = cycle (tl xs @ [hd xs])"
277 lemma cycle_decomp: "u \<noteq> [] \<Longrightarrow> cycle u = u @- cycle u"
278 proof (coinduction arbitrary: u)
279 case Eq_stream then show ?case using stream.collapse[of "cycle u"]
280 by (auto intro!: exI[of _ "tl u @ [hd u]"])
283 lemma cycle_Cons[code]: "cycle (x # xs) = x ## cycle (xs @ [x])"
284 by (subst cycle.ctr) simp
286 lemma cycle_rotated: "\<lbrakk>v \<noteq> []; cycle u = v @- s\<rbrakk> \<Longrightarrow> cycle (tl u @ [hd u]) = tl v @- s"
287 by (auto dest: arg_cong[of _ _ stl])
289 lemma stake_append: "stake n (u @- s) = take (min (length u) n) u @ stake (n - length u) s"
290 proof (induct n arbitrary: u)
291 case (Suc n) thus ?case by (cases u) auto
294 lemma stake_cycle_le[simp]:
295 assumes "u \<noteq> []" "n < length u"
296 shows "stake n (cycle u) = take n u"
297 using min_absorb2[OF less_imp_le_nat[OF assms(2)]]
298 by (subst cycle_decomp[OF assms(1)], subst stake_append) auto
300 lemma stake_cycle_eq[simp]: "u \<noteq> [] \<Longrightarrow> stake (length u) (cycle u) = u"
301 by (metis cycle_decomp stake_shift)
303 lemma sdrop_cycle_eq[simp]: "u \<noteq> [] \<Longrightarrow> sdrop (length u) (cycle u) = cycle u"
304 by (metis cycle_decomp sdrop_shift)
306 lemma stake_cycle_eq_mod_0[simp]: "\<lbrakk>u \<noteq> []; n mod length u = 0\<rbrakk> \<Longrightarrow>
307 stake n (cycle u) = concat (replicate (n div length u) u)"
308 by (induct "n div length u" arbitrary: n u) (auto simp: stake_add[symmetric])
310 lemma sdrop_cycle_eq_mod_0[simp]: "\<lbrakk>u \<noteq> []; n mod length u = 0\<rbrakk> \<Longrightarrow>
311 sdrop n (cycle u) = cycle u"
312 by (induct "n div length u" arbitrary: n u) (auto simp: sdrop_add[symmetric])
314 lemma stake_cycle: "u \<noteq> [] \<Longrightarrow>
315 stake n (cycle u) = concat (replicate (n div length u) u) @ take (n mod length u) u"
316 by (subst mod_div_equality[of n "length u", symmetric], unfold stake_add[symmetric]) auto
318 lemma sdrop_cycle: "u \<noteq> [] \<Longrightarrow> sdrop n (cycle u) = cycle (rotate (n mod length u) u)"
319 by (induct n arbitrary: u) (auto simp: rotate1_rotate_swap rotate1_hd_tl rotate_conv_mod[symmetric])
322 subsection {* iterated application of a function *}
324 primcorec siterate where
325 "shd (siterate f x) = x"
326 | "stl (siterate f x) = siterate f (f x)"
328 lemma stake_Suc: "stake (Suc n) s = stake n s @ [s !! n]"
329 by (induct n arbitrary: s) auto
331 lemma snth_siterate[simp]: "siterate f x !! n = (f^^n) x"
332 by (induct n arbitrary: x) (auto simp: funpow_swap1)
334 lemma sdrop_siterate[simp]: "sdrop n (siterate f x) = siterate f ((f^^n) x)"
335 by (induct n arbitrary: x) (auto simp: funpow_swap1)
337 lemma stake_siterate[simp]: "stake n (siterate f x) = map (\<lambda>n. (f^^n) x) [0 ..< n]"
338 by (induct n arbitrary: x) (auto simp del: stake.simps(2) simp: stake_Suc)
340 lemma sset_siterate: "sset (siterate f x) = {(f^^n) x | n. True}"
341 by (auto simp: sset_range)
343 lemma smap_siterate: "smap f (siterate f x) = siterate f (f x)"
344 by (coinduction arbitrary: x) auto
347 subsection {* stream repeating a single element *}
349 abbreviation "sconst \<equiv> siterate id"
351 lemma shift_replicate_sconst[simp]: "replicate n x @- sconst x = sconst x"
352 by (subst (3) stake_sdrop[symmetric]) (simp add: map_replicate_trivial)
354 lemma stream_all_same[simp]: "sset (sconst x) = {x}"
355 by (simp add: sset_siterate)
357 lemma same_cycle: "sconst x = cycle [x]"
360 lemma smap_sconst: "smap f (sconst x) = sconst (f x)"
363 lemma sconst_streams: "x \<in> A \<Longrightarrow> sconst x \<in> streams A"
364 by (simp add: streams_iff_sset)
367 subsection {* stream of natural numbers *}
369 abbreviation "fromN \<equiv> siterate Suc"
371 abbreviation "nats \<equiv> fromN 0"
373 lemma sset_fromN[simp]: "sset (fromN n) = {n ..}"
374 by (auto simp add: sset_siterate) arith
377 subsection {* flatten a stream of lists *}
380 "shd (flat ws) = hd (shd ws)"
381 | "stl (flat ws) = flat (if tl (shd ws) = [] then stl ws else tl (shd ws) ## stl ws)"
383 lemma flat_Cons[simp, code]: "flat ((x # xs) ## ws) = x ## flat (if xs = [] then ws else xs ## ws)"
384 by (subst flat.ctr) simp
386 lemma flat_Stream[simp]: "xs \<noteq> [] \<Longrightarrow> flat (xs ## ws) = xs @- flat ws"
389 lemma flat_unfold: "shd ws \<noteq> [] \<Longrightarrow> flat ws = shd ws @- flat (stl ws)"
392 lemma flat_snth: "\<forall>xs \<in> sset s. xs \<noteq> [] \<Longrightarrow> flat s !! n = (if n < length (shd s) then
393 shd s ! n else flat (stl s) !! (n - length (shd s)))"
394 by (metis flat_unfold not_less shd_sset shift_snth_ge shift_snth_less)
396 lemma sset_flat[simp]: "\<forall>xs \<in> sset s. xs \<noteq> [] \<Longrightarrow>
397 sset (flat s) = (\<Union>xs \<in> sset s. set xs)" (is "?P \<Longrightarrow> ?L = ?R")
399 fix x assume ?P "x : ?L"
400 then obtain m where "x = flat s !! m" by (metis image_iff sset_range)
401 with `?P` obtain n m' where "x = s !! n ! m'" "m' < length (s !! n)"
402 proof (atomize_elim, induct m arbitrary: s rule: less_induct)
405 proof (cases "y < length (shd s)")
406 case True thus ?thesis by (metis flat_snth less(2,3) snth.simps(1))
409 hence "x = flat (stl s) !! (y - length (shd s))" by (metis less(2,3) flat_snth)
411 { from less(2) have *: "length (shd s) > 0" by (cases s) simp_all
412 with False have "y > 0" by (cases y) simp_all
413 with * have "y - length (shd s) < y" by simp
415 moreover have "\<forall>xs \<in> sset (stl s). xs \<noteq> []" using less(2) by (cases s) auto
416 ultimately have "\<exists>n m'. x = stl s !! n ! m' \<and> m' < length (stl s !! n)" by (intro less(1)) auto
417 thus ?thesis by (metis snth.simps(2))
420 thus "x \<in> ?R" by (auto simp: sset_range dest!: nth_mem)
422 fix x xs assume "xs \<in> sset s" ?P "x \<in> set xs" thus "x \<in> ?L"
423 by (induct rule: sset_induct1)
424 (metis UnI1 flat_unfold shift.simps(1) sset_shift,
425 metis UnI2 flat_unfold shd_sset stl_sset sset_shift)
429 subsection {* merge a stream of streams *}
431 definition smerge :: "'a stream stream \<Rightarrow> 'a stream" where
432 "smerge ss = flat (smap (\<lambda>n. map (\<lambda>s. s !! n) (stake (Suc n) ss) @ stake n (ss !! n)) nats)"
434 lemma stake_nth[simp]: "m < n \<Longrightarrow> stake n s ! m = s !! m"
435 by (induct n arbitrary: s m) (auto simp: nth_Cons', metis Suc_pred snth.simps(2))
437 lemma snth_sset_smerge: "ss !! n !! m \<in> sset (smerge ss)"
438 proof (cases "n \<le> m")
439 case False thus ?thesis unfolding smerge_def
441 (auto simp: stream.set_map in_set_conv_nth simp del: stake.simps
442 intro!: exI[of _ n, OF disjI2] exI[of _ m, OF mp])
444 case True thus ?thesis unfolding smerge_def
446 (auto simp: stream.set_map in_set_conv_nth image_iff simp del: stake.simps snth.simps
447 intro!: exI[of _ m, OF disjI1] bexI[of _ "ss !! n"] exI[of _ n, OF mp])
450 lemma sset_smerge: "sset (smerge ss) = UNION (sset ss) sset"
452 fix x assume "x \<in> sset (smerge ss)"
453 thus "x \<in> UNION (sset ss) sset"
454 unfolding smerge_def by (subst (asm) sset_flat)
455 (auto simp: stream.set_map in_set_conv_nth sset_range simp del: stake.simps, fast+)
457 fix s x assume "s \<in> sset ss" "x \<in> sset s"
458 thus "x \<in> sset (smerge ss)" using snth_sset_smerge by (auto simp: sset_range)
462 subsection {* product of two streams *}
464 definition sproduct :: "'a stream \<Rightarrow> 'b stream \<Rightarrow> ('a \<times> 'b) stream" where
465 "sproduct s1 s2 = smerge (smap (\<lambda>x. smap (Pair x) s2) s1)"
467 lemma sset_sproduct: "sset (sproduct s1 s2) = sset s1 \<times> sset s2"
468 unfolding sproduct_def sset_smerge by (auto simp: stream.set_map)
471 subsection {* interleave two streams *}
473 primcorec sinterleave where
474 "shd (sinterleave s1 s2) = shd s1"
475 | "stl (sinterleave s1 s2) = sinterleave s2 (stl s1)"
477 lemma sinterleave_code[code]:
478 "sinterleave (x ## s1) s2 = x ## sinterleave s2 s1"
479 by (subst sinterleave.ctr) simp
481 lemma sinterleave_snth[simp]:
482 "even n \<Longrightarrow> sinterleave s1 s2 !! n = s1 !! (n div 2)"
483 "odd n \<Longrightarrow> sinterleave s1 s2 !! n = s2 !! (n div 2)"
484 by (induct n arbitrary: s1 s2)
485 (auto dest: even_nat_Suc_div_2 odd_nat_plus_one_div_two[folded nat_2])
487 lemma sset_sinterleave: "sset (sinterleave s1 s2) = sset s1 \<union> sset s2"
488 proof (intro equalityI subsetI)
489 fix x assume "x \<in> sset (sinterleave s1 s2)"
490 then obtain n where "x = sinterleave s1 s2 !! n" unfolding sset_range by blast
491 thus "x \<in> sset s1 \<union> sset s2" by (cases "even n") auto
493 fix x assume "x \<in> sset s1 \<union> sset s2"
494 thus "x \<in> sset (sinterleave s1 s2)"
496 assume "x \<in> sset s1"
497 then obtain n where "x = s1 !! n" unfolding sset_range by blast
498 hence "sinterleave s1 s2 !! (2 * n) = x" by simp
499 thus ?thesis unfolding sset_range by blast
501 assume "x \<in> sset s2"
502 then obtain n where "x = s2 !! n" unfolding sset_range by blast
503 hence "sinterleave s1 s2 !! (2 * n + 1) = x" by simp
504 thus ?thesis unfolding sset_range by blast
512 "shd (szip s1 s2) = (shd s1, shd s2)"
513 | "stl (szip s1 s2) = szip (stl s1) (stl s2)"
515 lemma szip_unfold[code]: "szip (Stream a s1) (Stream b s2) = Stream (a, b) (szip s1 s2)"
516 by (subst szip.ctr) simp
518 lemma snth_szip[simp]: "szip s1 s2 !! n = (s1 !! n, s2 !! n)"
519 by (induct n arbitrary: s1 s2) auto
522 subsection {* zip via function *}
524 primcorec smap2 where
525 "shd (smap2 f s1 s2) = f (shd s1) (shd s2)"
526 | "stl (smap2 f s1 s2) = smap2 f (stl s1) (stl s2)"
528 lemma smap2_unfold[code]:
529 "smap2 f (Stream a s1) (Stream b s2) = Stream (f a b) (smap2 f s1 s2)"
530 by (subst smap2.ctr) simp
533 "smap2 f s1 s2 = smap (split f) (szip s1 s2)"
534 by (coinduction arbitrary: s1 s2) auto