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<div class="document" id="plans-and-automatic-program-generation">
<h1 class="title">Plans and Automatic Program Generation</h1>
<p>Once you understand how <a class="reference external" href="rules/backward_chaining.html">backward-chaining</a> works, it is relatively easy to
do automatic program generation.</p>
<div class="section" id="adding-plans-to-backward-chaining-rules">
<h2>Adding Plans to Backward-Chaining Rules</h2>
<p>The way this is done is by attaching Python functions to
<a class="reference external" href="rules/backward_chaining.html">backward-chaining</a> <a class="reference external" href="rules/index.html">rules</a>. These functions are written in the <em>with</em>
clause at the end of each <a class="reference external" href="rules/index.html">rule</a> in the <a class="reference external" href="../pyke_syntax/krb_syntax/index.html">.krb file</a>. They don't affect how
the <a class="reference external" href="rules/index.html">rules</a> run to prove a goal, but are
gathered up to form a call graph that is returned along with the <a class="reference external" href="pattern_matching/pattern_variables.html">pattern
variable</a> bindings that <a class="reference external" href="../using_pyke/proving_goals.html">prove</a> the top-level goal.</p>
</div>
<div class="section" id="example">
<h2>Example</h2>
<p>Consider a small <a class="reference external" href="../knowledge_bases/rule_bases.html">rule base</a> to construct programs to transfer money between
bank accounts. Each <em>from_acct</em> and <em>to_acct</em> takes one of two forms:</p>
<ol class="arabic simple">
<li>(name, account_type)<ul>
<li>This is a local account with this bank.</li>
<li>Example: ('bruce', 'checking').</li>
</ul>
</li>
<li>(bank, name, account_type)<ul>
<li>This is a foreign account with another bank.</li>
<li>Example: ('my_other_bank', 'bruce', 'checking').</li>
</ul>
</li>
</ol>
<p>At least one of the bank accounts must be a local account.</p>
<p>Here's the example rule base:</p>
<pre class="literal-block">
1 transfer1
2 use transfer($from_acct, $to_acct) taking (amount)
3 when
4 withdraw($from_acct)
5 $$(amount)
6 deposit($to_acct)
7 $$(amount)
8 transfer2
9 use transfer($from_acct, $to_acct) taking (amount)
10 when
11 transfer_ach($from_acct, $to_acct)
12 $$(amount)
13 withdraw
14 use withdraw(($who, $acct_type)) taking (amount)
15 with
16 print "withdraw", amount, "from", $who, $acct_type
17 deposit
18 use deposit(($who, $acct_type)) taking (amount)
19 with
20 print "deposit", amount, "to", $who, $acct_type
21 transfer_ach1
22 use transfer_ach($from_acct, ($bank, $who, $acct_type)) taking (amount)
23 when
24 withdraw($from_acct)
25 $$(amount)
26 deposit((central_accts, ach_send_acct))
27 $$(amount)
28 with
29 print "send", amount, "to bank", $bank, "acct", $who, $acct_type
30 transfer_ach2
31 use transfer_ach($from_acct, $to_acct) taking (amount)
32 when
33 get_ach($from_acct)
34 $$(amount)
35 withdraw((central_accts, ach_recv_acct))
36 $$(amount)
37 deposit($to_acct)
38 $$(amount)
39 get_ach
40 use get_ach(($bank, $who, $acct_type)) taking (amount)
41 with
42 print "get", amount, "from bank", $bank, "acct", $who, $acct_type
</pre>
<div class="section" id="how-the-plan-functions-are-generated-for-this-example">
<h3>How the Plan Functions are Generated for This Example</h3>
<p>Each of these <a class="reference external" href="rules/index.html">rules</a> will have a plan function generated for it. These plan
functions are generated with the same name as the <a class="reference external" href="rules/index.html">rule</a> name. Thus, the
name of the generated Python plan function for the first rule would be
"transfer1".</p>
<p>The plan function generated for the first rule consists of two lines taken
from lines 5 and 7 of this example. The $$ in each of these lines will
be expanded to the subordinate plan function returned from the proof of
"withdraw($from_acct)" and "deposit($to_acct)" respectfully. The generated
plan function will be defined to take an "amount" parameter because of the
<em>taking</em> clause on line 2. This parameter is passed on to each of the
subordinate plan functions in lines 5 and 7.</p>
<p>The plan function generated for the "withdraw" rule on line 13 will have
the single line taken from line 16 in the <em>with</em> clause. The "$who" and
"$acct_type" <a class="reference external" href="pattern_matching/pattern_variables.html">pattern variables</a> will be expanded to constant values taken
from the values bound to these <a class="reference external" href="pattern_matching/pattern_variables.html">pattern variables</a> after the top-level
(transfer) goal has been proven.</p>
<p>Finally, the plan function generated for the "transfer_ach1" rule on line
21 will have three lines: two from the <em>when</em> clause (lines 25 and 27)
followed by one from the <em>with</em> clause (line 29). These lines will be
generated at the same indent level in the plan function even though they
are at different indent levels in the <a class="reference external" href="../pyke_syntax/krb_syntax/index.html">.krb file</a>.</p>
<p>For more detailed information about the options available for plans in the
<a class="reference external" href="../pyke_syntax/krb_syntax/index.html">.krb file</a>, see <a class="reference external" href="rules/backward_chaining.html">Bc_rule Syntax</a>.</p>
</div>
</div>
<div class="section" id="running-the-example">
<h2>Running the Example</h2>
<!-- This code is hidden. It will add '' to sys.path, change to the doc.examples
directory and store the directory path in __file__ for the code section
following:
>>> import sys
>>> if '' not in sys.path: sys.path.insert(0, '')
>>> import os
>>> os.chdir("../../examples")
>>> __file__ = os.getcwd() -->
<p>The plan is created as a byproduct of <a class="reference external" href="../using_pyke/proving_goals.html">proving</a> the goal:</p>
<blockquote>
<pre class="doctest-block">
>>> from pyke import knowledge_engine
</pre>
<pre class="doctest-block">
>>> engine = knowledge_engine.engine(__file__)
>>> engine.activate('plan_example')
>>> no_vars, plan1 = \
... engine.prove_1_goal(
... 'plan_example.transfer((bruce, checking), (bruce, savings))')
</pre>
</blockquote>
<p><tt class="docutils literal">plan1</tt> is now a program to transfer X amount
from 'bruce', 'checking' to 'bruce', 'savings'. Using the above rule names
as function names, plan1 looks like this:</p>
<div class="figure align-center">
<img alt="../images/plan1.png" src="../images/plan1.png" style="width: 187.0px; height: 118.0px;" />
<p class="caption">Plan1</p>
</div>
<p>And can be called like a standard function, passing the parameters
specified in the <em>taking</em> clause of the rules for the top-level goal
(transfer):</p>
<blockquote>
<pre class="doctest-block">
>>> plan1(100)
withdraw 100 from bruce checking
deposit 100 to bruce savings
</pre>
</blockquote>
<p>The program may be used multiple times:</p>
<blockquote>
<pre class="doctest-block">
>>> plan1(50)
withdraw 50 from bruce checking
deposit 50 to bruce savings
</pre>
</blockquote>
<p>Notice the strings: <tt class="docutils literal">bruce</tt>, <tt class="docutils literal">checking</tt> and <tt class="docutils literal">savings</tt> in the output.
These were specified as <a class="reference external" href="pattern_matching/pattern_variables.html">pattern variables</a> in the code and are <a class="reference external" href="../about_pyke/cooking_functions.html">cooked</a>
into the plan along with the function call graph.</p>
<p>Let's create a second program:</p>
<blockquote>
<pre class="doctest-block">
>>> no_vars, plan2 = \
... engine.prove_1_goal(
... 'plan_example.transfer((bruce, checking), '
... '(my_other_bank, bruce, savings))')
</pre>
</blockquote>
<p><tt class="docutils literal">plan2</tt> is now a program to transfer X amount
from 'my_other_bank', 'bruce', 'checking' to 'bruce', 'savings'.
Plan2 looks like this:</p>
<div class="figure align-center">
<img alt="../images/plan2.png" src="../images/plan2.png" style="width: 187.0px; height: 195.0px;" />
<p class="caption">Plan2</p>
</div>
<p>And is run just like plan1, but produces different results:</p>
<blockquote>
<pre class="doctest-block">
>>> plan2(200)
withdraw 200 from bruce checking
deposit 200 to central_accts ach_send_acct
send 200 to bank my_other_bank acct bruce savings
</pre>
</blockquote>
<p>And the final use case:</p>
<blockquote>
<pre class="doctest-block">
>>> no_vars, plan3 = \
... engine.prove_1_goal(
... 'plan_example.transfer((my_other_bank, bruce, checking), '
... '(bruce, savings))')
>>> plan3(150)
get 150 from bank my_other_bank acct bruce checking
withdraw 150 from central_accts ach_recv_acct
deposit 150 to bruce savings
</pre>
</blockquote>
<p>Plan3 looks like this:</p>
<div class="figure align-center">
<img alt="../images/plan3.png" src="../images/plan3.png" style="width: 264.0px; height: 198.0px;" />
<p class="caption">Plan3</p>
</div>
<p>Note that the same <em>transfer2</em> function is calling two different functions
(<em>transfer_ach1</em> and <em>transfer_ach2</em>) in plan2 and plan3. This shows how
different functions may be chosen based on the <a class="reference external" href="rules/index.html">rule</a> inferencing. Also
note that after the generation of plan3, plan2 is still valid; both may
still be called successfully, resulting in different calls from the initial
<em>transfer2</em> function.</p>
</div>
<div class="section" id="conclusion">
<h2>Conclusion</h2>
<p>So you can see that it quite easy to use Pyke to automatically combine
Python functions into programs!</p>
<p>It also allows data within each Python function to be specified using a
<a class="reference external" href="pattern_matching/pattern_variables.html">pattern variable</a> so that Pyke can customize these values to match the
specific situation.</p>
<p>If you would like to know more about how Pyke <em>cooks</em> (or customizes) your
Python functions, see <a class="reference external" href="../about_pyke/cooking_functions.html">Cooking Functions</a>.</p>
<!-- ADD_LINKS MARKER -->
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<div id="right-nav-div">
<h3>More:</h3>
<div class="right-item"><a href="statements.html">Statements</a><p>What is a <em>statement</em> in Pyke?</p>
</div>
<div class="right-item"><a href="pattern_matching/index.html">Pattern Matching</a><p>Explanation of <em>pattern matching</em> and <em>pattern variables</em>.</p>
</div>
<div class="right-item"><a href="rules/index.html">Rules</a><p>Explanation of <em>rules</em>, <em>forward-chaining</em> and <em>backward-chaining</em>.</p>
</div>
<div class="right-item"><a href="plans.html">Plans and Automatic Program Generation</a><p>Explanation of <em>plans</em> and automatic program generation.</p>
</div>
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Copyright © 2007-2009 Bruce Frederiksen
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