--- a/doc-src/TutorialI/Trie/document/Trie.tex Thu Jul 26 16:08:16 2012 +0200
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,297 +0,0 @@
-%
-\begin{isabellebody}%
-\def\isabellecontext{Trie}%
-%
-\isadelimtheory
-%
-\endisadelimtheory
-%
-\isatagtheory
-%
-\endisatagtheory
-{\isafoldtheory}%
-%
-\isadelimtheory
-%
-\endisadelimtheory
-%
-\begin{isamarkuptext}%
-To minimize running time, each node of a trie should contain an array that maps
-letters to subtries. We have chosen a
-representation where the subtries are held in an association list, i.e.\ a
-list of (letter,trie) pairs. Abstracting over the alphabet \isa{{\isaliteral{27}{\isacharprime}}a} and the
-values \isa{{\isaliteral{27}{\isacharprime}}v} we define a trie as follows:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-\isacommand{datatype}\isamarkupfalse%
-\ {\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}{\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}trie\ {\isaliteral{3D}{\isacharequal}}\ Trie\ \ {\isaliteral{22}{\isachardoublequoteopen}}{\isaliteral{27}{\isacharprime}}v\ option{\isaliteral{22}{\isachardoublequoteclose}}\ \ {\isaliteral{22}{\isachardoublequoteopen}}{\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a\ {\isaliteral{2A}{\isacharasterisk}}\ {\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}{\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}trie{\isaliteral{29}{\isacharparenright}}list{\isaliteral{22}{\isachardoublequoteclose}}%
-\begin{isamarkuptext}%
-\noindent
-\index{datatypes!and nested recursion}%
-The first component is the optional value, the second component the
-association list of subtries. This is an example of nested recursion involving products,
-which is fine because products are datatypes as well.
-We define two selector functions:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-\isacommand{primrec}\isamarkupfalse%
-\ {\isaliteral{22}{\isachardoublequoteopen}}value{\isaliteral{22}{\isachardoublequoteclose}}\ {\isaliteral{3A}{\isacharcolon}}{\isaliteral{3A}{\isacharcolon}}\ {\isaliteral{22}{\isachardoublequoteopen}}{\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}{\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}trie\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{27}{\isacharprime}}v\ option{\isaliteral{22}{\isachardoublequoteclose}}\ \isakeyword{where}\isanewline
-{\isaliteral{22}{\isachardoublequoteopen}}value{\isaliteral{28}{\isacharparenleft}}Trie\ ov\ al{\isaliteral{29}{\isacharparenright}}\ {\isaliteral{3D}{\isacharequal}}\ ov{\isaliteral{22}{\isachardoublequoteclose}}\isanewline
-\isacommand{primrec}\isamarkupfalse%
-\ alist\ {\isaliteral{3A}{\isacharcolon}}{\isaliteral{3A}{\isacharcolon}}\ {\isaliteral{22}{\isachardoublequoteopen}}{\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}{\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}trie\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a\ {\isaliteral{2A}{\isacharasterisk}}\ {\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}{\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}trie{\isaliteral{29}{\isacharparenright}}list{\isaliteral{22}{\isachardoublequoteclose}}\ \isakeyword{where}\isanewline
-{\isaliteral{22}{\isachardoublequoteopen}}alist{\isaliteral{28}{\isacharparenleft}}Trie\ ov\ al{\isaliteral{29}{\isacharparenright}}\ {\isaliteral{3D}{\isacharequal}}\ al{\isaliteral{22}{\isachardoublequoteclose}}%
-\begin{isamarkuptext}%
-\noindent
-Association lists come with a generic lookup function. Its result
-involves type \isa{option} because a lookup can fail:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-\isacommand{primrec}\isamarkupfalse%
-\ assoc\ {\isaliteral{3A}{\isacharcolon}}{\isaliteral{3A}{\isacharcolon}}\ {\isaliteral{22}{\isachardoublequoteopen}}{\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}key\ {\isaliteral{2A}{\isacharasterisk}}\ {\isaliteral{27}{\isacharprime}}val{\isaliteral{29}{\isacharparenright}}list\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{27}{\isacharprime}}key\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{27}{\isacharprime}}val\ option{\isaliteral{22}{\isachardoublequoteclose}}\ \isakeyword{where}\isanewline
-{\isaliteral{22}{\isachardoublequoteopen}}assoc\ {\isaliteral{5B}{\isacharbrackleft}}{\isaliteral{5D}{\isacharbrackright}}\ x\ {\isaliteral{3D}{\isacharequal}}\ None{\isaliteral{22}{\isachardoublequoteclose}}\ {\isaliteral{7C}{\isacharbar}}\isanewline
-{\isaliteral{22}{\isachardoublequoteopen}}assoc\ {\isaliteral{28}{\isacharparenleft}}p{\isaliteral{23}{\isacharhash}}ps{\isaliteral{29}{\isacharparenright}}\ x\ {\isaliteral{3D}{\isacharequal}}\isanewline
-\ \ \ {\isaliteral{28}{\isacharparenleft}}let\ {\isaliteral{28}{\isacharparenleft}}a{\isaliteral{2C}{\isacharcomma}}b{\isaliteral{29}{\isacharparenright}}\ {\isaliteral{3D}{\isacharequal}}\ p\ in\ if\ a{\isaliteral{3D}{\isacharequal}}x\ then\ Some\ b\ else\ assoc\ ps\ x{\isaliteral{29}{\isacharparenright}}{\isaliteral{22}{\isachardoublequoteclose}}%
-\begin{isamarkuptext}%
-Now we can define the lookup function for tries. It descends into the trie
-examining the letters of the search string one by one. As
-recursion on lists is simpler than on tries, let us express this as primitive
-recursion on the search string argument:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-\isacommand{primrec}\isamarkupfalse%
-\ lookup\ {\isaliteral{3A}{\isacharcolon}}{\isaliteral{3A}{\isacharcolon}}\ {\isaliteral{22}{\isachardoublequoteopen}}{\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}{\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}trie\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{27}{\isacharprime}}a\ list\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{27}{\isacharprime}}v\ option{\isaliteral{22}{\isachardoublequoteclose}}\ \isakeyword{where}\isanewline
-{\isaliteral{22}{\isachardoublequoteopen}}lookup\ t\ {\isaliteral{5B}{\isacharbrackleft}}{\isaliteral{5D}{\isacharbrackright}}\ {\isaliteral{3D}{\isacharequal}}\ value\ t{\isaliteral{22}{\isachardoublequoteclose}}\ {\isaliteral{7C}{\isacharbar}}\isanewline
-{\isaliteral{22}{\isachardoublequoteopen}}lookup\ t\ {\isaliteral{28}{\isacharparenleft}}a{\isaliteral{23}{\isacharhash}}as{\isaliteral{29}{\isacharparenright}}\ {\isaliteral{3D}{\isacharequal}}\ {\isaliteral{28}{\isacharparenleft}}case\ assoc\ {\isaliteral{28}{\isacharparenleft}}alist\ t{\isaliteral{29}{\isacharparenright}}\ a\ of\isanewline
-\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ None\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ None\isanewline
-\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {\isaliteral{7C}{\isacharbar}}\ Some\ at\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ lookup\ at\ as{\isaliteral{29}{\isacharparenright}}{\isaliteral{22}{\isachardoublequoteclose}}%
-\begin{isamarkuptext}%
-As a first simple property we prove that looking up a string in the empty
-trie \isa{Trie\ None\ {\isaliteral{5B}{\isacharbrackleft}}{\isaliteral{5D}{\isacharbrackright}}} always returns \isa{None}. The proof merely
-distinguishes the two cases whether the search string is empty or not:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-\isacommand{lemma}\isamarkupfalse%
-\ {\isaliteral{5B}{\isacharbrackleft}}simp{\isaliteral{5D}{\isacharbrackright}}{\isaliteral{3A}{\isacharcolon}}\ {\isaliteral{22}{\isachardoublequoteopen}}lookup\ {\isaliteral{28}{\isacharparenleft}}Trie\ None\ {\isaliteral{5B}{\isacharbrackleft}}{\isaliteral{5D}{\isacharbrackright}}{\isaliteral{29}{\isacharparenright}}\ as\ {\isaliteral{3D}{\isacharequal}}\ None{\isaliteral{22}{\isachardoublequoteclose}}\isanewline
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isatagproof
-\isacommand{apply}\isamarkupfalse%
-{\isaliteral{28}{\isacharparenleft}}case{\isaliteral{5F}{\isacharunderscore}}tac\ as{\isaliteral{2C}{\isacharcomma}}\ simp{\isaliteral{5F}{\isacharunderscore}}all{\isaliteral{29}{\isacharparenright}}\isanewline
-\isacommand{done}\isamarkupfalse%
-%
-\endisatagproof
-{\isafoldproof}%
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\begin{isamarkuptext}%
-Things begin to get interesting with the definition of an update function
-that adds a new (string, value) pair to a trie, overwriting the old value
-associated with that string:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-\isacommand{primrec}\isamarkupfalse%
-\ update{\isaliteral{3A}{\isacharcolon}}{\isaliteral{3A}{\isacharcolon}}\ {\isaliteral{22}{\isachardoublequoteopen}}{\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}{\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}trie\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{27}{\isacharprime}}a\ list\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{27}{\isacharprime}}v\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}{\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}trie{\isaliteral{22}{\isachardoublequoteclose}}\ \isakeyword{where}\isanewline
-{\isaliteral{22}{\isachardoublequoteopen}}update\ t\ {\isaliteral{5B}{\isacharbrackleft}}{\isaliteral{5D}{\isacharbrackright}}\ \ \ \ \ v\ {\isaliteral{3D}{\isacharequal}}\ Trie\ {\isaliteral{28}{\isacharparenleft}}Some\ v{\isaliteral{29}{\isacharparenright}}\ {\isaliteral{28}{\isacharparenleft}}alist\ t{\isaliteral{29}{\isacharparenright}}{\isaliteral{22}{\isachardoublequoteclose}}\ {\isaliteral{7C}{\isacharbar}}\isanewline
-{\isaliteral{22}{\isachardoublequoteopen}}update\ t\ {\isaliteral{28}{\isacharparenleft}}a{\isaliteral{23}{\isacharhash}}as{\isaliteral{29}{\isacharparenright}}\ v\ {\isaliteral{3D}{\isacharequal}}\isanewline
-\ \ \ {\isaliteral{28}{\isacharparenleft}}let\ tt\ {\isaliteral{3D}{\isacharequal}}\ {\isaliteral{28}{\isacharparenleft}}case\ assoc\ {\isaliteral{28}{\isacharparenleft}}alist\ t{\isaliteral{29}{\isacharparenright}}\ a\ of\isanewline
-\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ None\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ Trie\ None\ {\isaliteral{5B}{\isacharbrackleft}}{\isaliteral{5D}{\isacharbrackright}}\ {\isaliteral{7C}{\isacharbar}}\ Some\ at\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ at{\isaliteral{29}{\isacharparenright}}\isanewline
-\ \ \ \ in\ Trie\ {\isaliteral{28}{\isacharparenleft}}value\ t{\isaliteral{29}{\isacharparenright}}\ {\isaliteral{28}{\isacharparenleft}}{\isaliteral{28}{\isacharparenleft}}a{\isaliteral{2C}{\isacharcomma}}update\ tt\ as\ v{\isaliteral{29}{\isacharparenright}}\ {\isaliteral{23}{\isacharhash}}\ alist\ t{\isaliteral{29}{\isacharparenright}}{\isaliteral{29}{\isacharparenright}}{\isaliteral{22}{\isachardoublequoteclose}}%
-\begin{isamarkuptext}%
-\noindent
-The base case is obvious. In the recursive case the subtrie
-\isa{tt} associated with the first letter \isa{a} is extracted,
-recursively updated, and then placed in front of the association list.
-The old subtrie associated with \isa{a} is still in the association list
-but no longer accessible via \isa{assoc}. Clearly, there is room here for
-optimizations!
-
-Before we start on any proofs about \isa{update} we tell the simplifier to
-expand all \isa{let}s and to split all \isa{case}-constructs over
-options:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-\isacommand{declare}\isamarkupfalse%
-\ Let{\isaliteral{5F}{\isacharunderscore}}def{\isaliteral{5B}{\isacharbrackleft}}simp{\isaliteral{5D}{\isacharbrackright}}\ option{\isaliteral{2E}{\isachardot}}split{\isaliteral{5B}{\isacharbrackleft}}split{\isaliteral{5D}{\isacharbrackright}}%
-\begin{isamarkuptext}%
-\noindent
-The reason becomes clear when looking (probably after a failed proof
-attempt) at the body of \isa{update}: it contains both
-\isa{let} and a case distinction over type \isa{option}.
-
-Our main goal is to prove the correct interaction of \isa{update} and
-\isa{lookup}:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-\isacommand{theorem}\isamarkupfalse%
-\ {\isaliteral{22}{\isachardoublequoteopen}}{\isaliteral{5C3C666F72616C6C3E}{\isasymforall}}t\ v\ bs{\isaliteral{2E}{\isachardot}}\ lookup\ {\isaliteral{28}{\isacharparenleft}}update\ t\ as\ v{\isaliteral{29}{\isacharparenright}}\ bs\ {\isaliteral{3D}{\isacharequal}}\isanewline
-\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {\isaliteral{28}{\isacharparenleft}}if\ as{\isaliteral{3D}{\isacharequal}}bs\ then\ Some\ v\ else\ lookup\ t\ bs{\isaliteral{29}{\isacharparenright}}{\isaliteral{22}{\isachardoublequoteclose}}%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isatagproof
-%
-\begin{isamarkuptxt}%
-\noindent
-Our plan is to induct on \isa{as}; hence the remaining variables are
-quantified. From the definitions it is clear that induction on either
-\isa{as} or \isa{bs} is required. The choice of \isa{as} is
-guided by the intuition that simplification of \isa{lookup} might be easier
-if \isa{update} has already been simplified, which can only happen if
-\isa{as} is instantiated.
-The start of the proof is conventional:%
-\end{isamarkuptxt}%
-\isamarkuptrue%
-\isacommand{apply}\isamarkupfalse%
-{\isaliteral{28}{\isacharparenleft}}induct{\isaliteral{5F}{\isacharunderscore}}tac\ as{\isaliteral{2C}{\isacharcomma}}\ auto{\isaliteral{29}{\isacharparenright}}%
-\begin{isamarkuptxt}%
-\noindent
-Unfortunately, this time we are left with three intimidating looking subgoals:
-\begin{isabelle}
-~1.~\dots~{\isasymLongrightarrow}~lookup~\dots~bs~=~lookup~t~bs\isanewline
-~2.~\dots~{\isasymLongrightarrow}~lookup~\dots~bs~=~lookup~t~bs\isanewline
-~3.~\dots~{\isasymLongrightarrow}~lookup~\dots~bs~=~lookup~t~bs
-\end{isabelle}
-Clearly, if we want to make headway we have to instantiate \isa{bs} as
-well now. It turns out that instead of induction, case distinction
-suffices:%
-\end{isamarkuptxt}%
-\isamarkuptrue%
-\isacommand{apply}\isamarkupfalse%
-{\isaliteral{28}{\isacharparenleft}}case{\isaliteral{5F}{\isacharunderscore}}tac{\isaliteral{5B}{\isacharbrackleft}}{\isaliteral{21}{\isacharbang}}{\isaliteral{5D}{\isacharbrackright}}\ bs{\isaliteral{2C}{\isacharcomma}}\ auto{\isaliteral{29}{\isacharparenright}}\isanewline
-\isacommand{done}\isamarkupfalse%
-%
-\endisatagproof
-{\isafoldproof}%
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\begin{isamarkuptext}%
-\noindent
-\index{subgoal numbering}%
-All methods ending in \isa{tac} take an optional first argument that
-specifies the range of subgoals they are applied to, where \isa{{\isaliteral{5B}{\isacharbrackleft}}{\isaliteral{21}{\isacharbang}}{\isaliteral{5D}{\isacharbrackright}}} means
-all subgoals, i.e.\ \isa{{\isaliteral{5B}{\isacharbrackleft}}{\isadigit{1}}{\isaliteral{2D}{\isacharminus}}{\isadigit{3}}{\isaliteral{5D}{\isacharbrackright}}} in our case. Individual subgoal numbers,
-e.g. \isa{{\isaliteral{5B}{\isacharbrackleft}}{\isadigit{2}}{\isaliteral{5D}{\isacharbrackright}}} are also allowed.
-
-This proof may look surprisingly straightforward. However, note that this
-comes at a cost: the proof script is unreadable because the intermediate
-proof states are invisible, and we rely on the (possibly brittle) magic of
-\isa{auto} (\isa{simp{\isaliteral{5F}{\isacharunderscore}}all} will not do --- try it) to split the subgoals
-of the induction up in such a way that case distinction on \isa{bs} makes
-sense and solves the proof.
-
-\begin{exercise}
- Modify \isa{update} (and its type) such that it allows both insertion and
- deletion of entries with a single function. Prove the corresponding version
- of the main theorem above.
- Optimize your function such that it shrinks tries after
- deletion if possible.
-\end{exercise}
-
-\begin{exercise}
- Write an improved version of \isa{update} that does not suffer from the
- space leak (pointed out above) caused by not deleting overwritten entries
- from the association list. Prove the main theorem for your improved
- \isa{update}.
-\end{exercise}
-
-\begin{exercise}
- Conceptually, each node contains a mapping from letters to optional
- subtries. Above we have implemented this by means of an association
- list. Replay the development replacing \isa{{\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a\ {\isaliteral{5C3C74696D65733E}{\isasymtimes}}\ {\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}\ {\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}\ trie{\isaliteral{29}{\isacharparenright}}\ list}
- with \isa{{\isaliteral{27}{\isacharprime}}a\ {\isaliteral{5C3C52696768746172726F773E}{\isasymRightarrow}}\ {\isaliteral{28}{\isacharparenleft}}{\isaliteral{27}{\isacharprime}}a{\isaliteral{2C}{\isacharcomma}}\ {\isaliteral{27}{\isacharprime}}v{\isaliteral{29}{\isacharparenright}}\ trie\ option}.
-\end{exercise}%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isatagproof
-%
-\endisatagproof
-{\isafoldproof}%
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isatagproof
-%
-\endisatagproof
-{\isafoldproof}%
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isatagproof
-%
-\endisatagproof
-{\isafoldproof}%
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isatagproof
-%
-\endisatagproof
-{\isafoldproof}%
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isatagproof
-%
-\endisatagproof
-{\isafoldproof}%
-%
-\isadelimproof
-%
-\endisadelimproof
-%
-\isadelimtheory
-%
-\endisadelimtheory
-%
-\isatagtheory
-%
-\endisatagtheory
-{\isafoldtheory}%
-%
-\isadelimtheory
-%
-\endisadelimtheory
-\end{isabellebody}%
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