124 lines
3.6 KiB
HTML
124 lines
3.6 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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<!Originally converted to HTML using LaTeX2HTML 95 (Thu Jan 19 1995) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<HEAD>
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<TITLE> Summary of Rules</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Summary of Rules">
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<meta name="keywords" value="lp">
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<meta name="resource-type" value="document">
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<meta name="distribution" value="global">
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<P>
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<BR> <HR>
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<A HREF="node49.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A>
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<A HREF="node41.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A>
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<A HREF="node47.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="previous_motif.gif"></A> <BR>
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<A HREF="lp.html"><B>Contents</B></A>
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<B> Next:</B>
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<A HREF="node49.html"> Exercises</A>
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<B>Up:</B>
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<A HREF="node41.html"> Programming Techniques</A>
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<B> Previous:</B>
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<A HREF="node47.html"> Abstraction</A>
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<BR> <HR> <P>
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<H1> Summary of Rules</H1>
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<P>
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<DL COMPACT><DT>1.
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<DD> When recurring on a list, do three things:
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<DL COMPACT><DT>a.
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<DD> check for the termination condition;
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<DT>b.
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<DD> use the first element of the list;
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<DT>c.
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<DD> recur with the ``rest'' of the list.
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<P>
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</DL>
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<DT>2.
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<DD> If a function builds a list using ``cons,'' return () at
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the terminating line.
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<DT>3.
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<DD> When recurring on a nested list, do three things:
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<DL COMPACT><DT>a.
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<DD> check for the termination condition;
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<DT>b.
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<DD> check if the first element of the list is an
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atom or a list;
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<DT>c.
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<DD> recur with the ``first'' and the ``rest'' of the list.
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<P>
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</DL>
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<DT>4.
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<DD> When evaluating an expression, do three things:
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<DL COMPACT><DT>a.
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<DD> check for the termination condition;
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<DT>b.
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<DD> identify operator;
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<DT>c.
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<DD> apply operator to recursive calls on the operands.
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<P>
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</DL>
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<DT>5.
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<DD> When building a number value using +, return 0 at the
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terminating line. When building a number value using
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*, return 1 at the terminating line.
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<DT>6.
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<DD> When recurring on a number, do three things:
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<DL COMPACT><DT>a.
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<DD> check for the termination condition;
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<DT>b.
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<DD> use the number in some form;
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<DT>c.
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<DD> recur with a changed form of the number.
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<P>
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</DL>
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<DT>7.
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<DD> To ensure proper termination do two things:
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<DL COMPACT><DT>a.
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<DD> make sure that you are changing at least one argument in your
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recursive call;
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<DT>b.
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<DD> make sure that your test for termination looks at the arguments that
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change in the recursive call.
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<P>
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</DL>
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<DT>8.
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<DD> Two simple cases may occur when changing an argument in
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a recursive call:
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<DL COMPACT><DT>a.
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<DD> if you are using ``rest'' to change an argument which is a list,
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use ``null'' in the test for termination;
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<DT>b.
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<DD> if you are decreasing an argument which is a number, compare
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it with 0 in the test for termination.
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<P>
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</DL>
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<DT>9.
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<DD> Use ``let'' to reduce the number of function calls.
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<P>
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<DT>10.
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<DD> Encapsulate program fragments into new functions to
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improve clarity.
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<P>
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<DT>11.
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<DD> Encapsulate repeated program fragments into new functions
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to reduce program size.
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<P>
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</DL><BR> <HR>
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<A HREF="node49.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A>
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<A HREF="node41.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A>
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<A HREF="node47.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="previous_motif.gif"></A> <BR>
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<A HREF="lp.html"><B>Contents</B></A>
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<B> Next:</B>
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<A HREF="node49.html"> Exercises</A>
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<B>Up:</B>
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<A HREF="node41.html"> Programming Techniques</A>
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<B> Previous:</B>
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<A HREF="node47.html"> Abstraction</A>
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<BR> <HR> <P>
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<BR> <HR>
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<P>
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<ADDRESS>
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<I>© Colin Allen & Maneesh Dhagat <BR>
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March 2007 </I>
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</ADDRESS>
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</BODY>
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