61 lines
2.1 KiB
HTML
61 lines
2.1 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> Reading</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Reading">
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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="node62.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A>
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<A HREF="node58.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A>
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<A HREF="node60.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="node62.html"> Input and Output </A>
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<B>Up:</B>
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<A HREF="node58.html"> Input and Output</A>
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<B> Previous:</B>
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<A HREF="node60.html"> Nicer Output Using </A>
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<BR> <HR> <P>
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<H1> Reading</H1>
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<P>
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Input from the keyboard is controlled using read, read-line, and read-char.
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<P>
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Read expects to receive a well-formed Lisp expression, i.e. an atom, list or string. It will not return a value until a complete expression has been entered -- in other words all opening parentheses or quotes must be matched.
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<P>
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Here is f-to-c using read:
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<P>
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<BLOCKQUOTE>
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<PRE>(defun f-to-c ()
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(format t "~%Please enter Fahrenheit temperature: ")
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(let* ((ftemp (read))
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(ctemp (* (- ftemp 32) 5/9)))
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(format t
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"~%~s degrees Fahrenheit is ~s degrees Celsius~%"
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ftemp
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(float ctemp)) ;; print floated value
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ctemp)) ;; return ratio value
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> (f-to-c)
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Please enter Fahrenheit temperature: 56 ;; user enters 56
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56 degrees Fahrenheit is 13.333333333333333 degrees Celsius
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40/3
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</PRE>
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</BLOCKQUOTE>
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Read-line always returns a string. Read-line will take in everything until the return key is pressed and return a string containing all the characters typed. Read-char reads and returns a single character.
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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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