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