80 lines
2.3 KiB
HTML
80 lines
2.3 KiB
HTML
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<!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> Lists</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Lists">
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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="node7.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A>
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<A HREF="node4.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A>
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<A HREF="node5.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="node7.html"> Some Primitive Functions</A>
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<B>Up:</B>
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<A HREF="node4.html"> Basic Data Types</A>
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<B> Previous:</B>
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<A HREF="node5.html"> Atoms</A>
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<BR> <HR> <P>
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<H2> Lists</H2>
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<P>
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The second rule of evaluation concerns lists. The interpreter treats
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any list as containing the name of a function followed by the
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arguments to the function. Schematically then, a list is read like
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this:
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<P>
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<BLOCKQUOTE>
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<PRE>(name-of-function first-argument second-argument ...)
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</PRE>
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</BLOCKQUOTE>
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For example, try the following:
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<P>
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<BLOCKQUOTE>
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<PRE>> (+ 2 13 45)
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60
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</PRE>
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</BLOCKQUOTE>
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In this case, the interpreter applied the function + to the evaluated
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arguments and return with the value 60. Since the numbers are
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predefined, eval finds values for all the arguments, and everyone is
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happy. You could also enter:
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<P>
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<BLOCKQUOTE>
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<PRE>> (+ my-age 1)
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11
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</PRE>
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</BLOCKQUOTE>
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This works fine because my-age is evaluated and the value 10 is found
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(assuming you did just what was described in the section above).
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However:
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<P>
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<BLOCKQUOTE>
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<PRE>> (+ your-age 1)
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</PRE>
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</BLOCKQUOTE>
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will generate an error (unbound variable your-age).
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<P>
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Also, if you attempt to use something that is not a function, you
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will generate an error message. So, for example, typing
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<P>
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<BLOCKQUOTE>
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<PRE>> (foo 1 3 4)
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</PRE>
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</BLOCKQUOTE>
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causes an error (undefined function foo), unless you had previously
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defined foo to be a function. (More on defining functions in a later
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chapter).
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<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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