00000004.htm

一份很好的linux入门资料

＞<I>&nbsp;(push&nbsp;4&nbsp;a)&nbsp;</I><BR>
(4)&nbsp;<BR>
＞<I>&nbsp;(push&nbsp;5&nbsp;a)&nbsp;</I><BR>
(5&nbsp;4)&nbsp;<BR>
＞<I>&nbsp;(pop&nbsp;a)&nbsp;</I><BR>
5&nbsp;<BR>
＞<I>&nbsp;a&nbsp;</I><BR>
(4)&nbsp;<BR>
＞<I>&nbsp;(pop&nbsp;a)&nbsp;</I><BR>
4&nbsp;<BR>
＞<I>&nbsp;(pop&nbsp;a)&nbsp;</I><BR>
NIL&nbsp;<BR>
＞<I>&nbsp;a&nbsp;</I><BR>
NIL&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Functions&nbsp;<BR>
&nbsp;<BR>
You&nbsp;saw&nbsp;one&nbsp;example&nbsp;of&nbsp;a&nbsp;function&nbsp;above.&nbsp;Here&nbsp;are&nbsp;some&nbsp;more:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(+&nbsp;3&nbsp;4&nbsp;5&nbsp;6)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;this&nbsp;function&nbsp;takes&nbsp;any&nbsp;number&nbsp;of&nbsp;arguments&nbsp;</I><BR>
18&nbsp;<BR>
＞<I>&nbsp;(+&nbsp;(+&nbsp;3&nbsp;4)&nbsp;(+&nbsp;(+&nbsp;4&nbsp;5)&nbsp;6))&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;isn't&nbsp;prefix&nbsp;notation&nbsp;fun?&nbsp;</I><BR>
22&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;foo&nbsp;(x&nbsp;y)&nbsp;(+&nbsp;x&nbsp;y&nbsp;5))&nbsp;&nbsp;&nbsp;;defining&nbsp;a&nbsp;function&nbsp;</I><BR>
FOO&nbsp;<BR>
＞<I>&nbsp;(foo&nbsp;5&nbsp;0)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;calling&nbsp;a&nbsp;function&nbsp;</I><BR>
10&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;fact&nbsp;(x)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;a&nbsp;recursive&nbsp;function&nbsp;</I><BR>
&nbsp;&nbsp;&nbsp;&nbsp;(if&nbsp;(&gt;&nbsp;x&nbsp;0)&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(*&nbsp;x&nbsp;(fact&nbsp;(-&nbsp;x&nbsp;1)))&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1&nbsp;<BR>
&nbsp;&nbsp;)&nbsp;)&nbsp;<BR>
FACT&nbsp;<BR>
＞<I>&nbsp;(fact&nbsp;5)&nbsp;</I><BR>
120&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;a&nbsp;(x)&nbsp;(if&nbsp;(=&nbsp;x&nbsp;0)&nbsp;t&nbsp;(b&nbsp;(-&nbsp;x))))&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;mutually&nbsp;recursive&nbsp;functions&nbsp;</I><BR>
A&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;b&nbsp;(x)&nbsp;(if&nbsp;(&gt;&nbsp;x&nbsp;0)&nbsp;(a&nbsp;(-&nbsp;x&nbsp;1))&nbsp;(a&nbsp;(+&nbsp;x&nbsp;1))))&nbsp;</I><BR>
B&nbsp;<BR>
＞<I>&nbsp;(a&nbsp;5)&nbsp;</I><BR>
T&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;bar&nbsp;(x)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;a&nbsp;function&nbsp;with&nbsp;multiple&nbsp;statements&nbsp;in&nbsp;</I><BR>
&nbsp;&nbsp;&nbsp;&nbsp;(setq&nbsp;x&nbsp;(*&nbsp;x&nbsp;3))&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;its&nbsp;body&nbsp;--&nbsp;it&nbsp;will&nbsp;return&nbsp;the&nbsp;value&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;(setq&nbsp;x&nbsp;(/&nbsp;x&nbsp;2))&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;returned&nbsp;by&nbsp;its&nbsp;final&nbsp;statement&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;(+&nbsp;x&nbsp;4)&nbsp;<BR>
&nbsp;&nbsp;)&nbsp;<BR>
BAR&nbsp;<BR>
＞<I>&nbsp;(bar&nbsp;6)&nbsp;</I><BR>
13&nbsp;<BR>
&nbsp;<BR>
When&nbsp;we&nbsp;defined&nbsp;foo,&nbsp;we&nbsp;gave&nbsp;it&nbsp;two&nbsp;arguments,&nbsp;x&nbsp;and&nbsp;y.&nbsp;Now&nbsp;when&nbsp;we&nbsp;<BR>
call&nbsp;foo,&nbsp;we&nbsp;are&nbsp;required&nbsp;to&nbsp;provide&nbsp;exactly&nbsp;two&nbsp;arguments:&nbsp;the&nbsp;first&nbsp;<BR>
will&nbsp;become&nbsp;the&nbsp;value&nbsp;of&nbsp;x&nbsp;for&nbsp;the&nbsp;duration&nbsp;of&nbsp;the&nbsp;call&nbsp;to&nbsp;foo,&nbsp;and&nbsp;the&nbsp;<BR>
second&nbsp;will&nbsp;become&nbsp;the&nbsp;value&nbsp;of&nbsp;y&nbsp;for&nbsp;the&nbsp;duration&nbsp;of&nbsp;the&nbsp;call.&nbsp;In&nbsp;<BR>
LISP,&nbsp;most&nbsp;variables&nbsp;are&nbsp;lexically&nbsp;scoped;&nbsp;that&nbsp;is,&nbsp;if&nbsp;foo&nbsp;calls&nbsp;bar&nbsp;<BR>
and&nbsp;bar&nbsp;tries&nbsp;to&nbsp;reference&nbsp;x,&nbsp;bar&nbsp;will&nbsp;not&nbsp;get&nbsp;foo's&nbsp;value&nbsp;for&nbsp;x.&nbsp;<BR>
&nbsp;<BR>
The&nbsp;process&nbsp;of&nbsp;assigning&nbsp;a&nbsp;symbol&nbsp;a&nbsp;value&nbsp;for&nbsp;the&nbsp;duration&nbsp;of&nbsp;some&nbsp;<BR>
lexical&nbsp;scope&nbsp;is&nbsp;called&nbsp;binding.&nbsp;<BR>
&nbsp;<BR>
You&nbsp;can&nbsp;specify&nbsp;optional&nbsp;arguments&nbsp;for&nbsp;your&nbsp;functions.&nbsp;Any&nbsp;argument&nbsp;<BR>
after&nbsp;the&nbsp;symbol&nbsp;&amp;optional&nbsp;is&nbsp;optional:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;bar&nbsp;(x&nbsp;&amp;optional&nbsp;y)&nbsp;(if&nbsp;y&nbsp;x&nbsp;0))&nbsp;</I><BR>
BAR&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;baaz&nbsp;(&amp;optional&nbsp;(x&nbsp;3)&nbsp;(z&nbsp;10))&nbsp;(+&nbsp;x&nbsp;z))&nbsp;</I><BR>
BAAZ&nbsp;<BR>
＞<I>&nbsp;(bar&nbsp;5)&nbsp;</I><BR>
0&nbsp;<BR>
＞<I>&nbsp;(bar&nbsp;5&nbsp;t)&nbsp;</I><BR>
5&nbsp;<BR>
＞<I>&nbsp;(baaz&nbsp;5)&nbsp;</I><BR>
15&nbsp;<BR>
＞<I>&nbsp;(baaz&nbsp;5&nbsp;6)&nbsp;</I><BR>
11&nbsp;<BR>
＞<I>&nbsp;(baaz)&nbsp;</I><BR>
13&nbsp;<BR>
&nbsp;<BR>
It&nbsp;is&nbsp;legal&nbsp;to&nbsp;call&nbsp;the&nbsp;function&nbsp;bar&nbsp;with&nbsp;either&nbsp;one&nbsp;or&nbsp;two&nbsp;arguments.&nbsp;<BR>
If&nbsp;it&nbsp;is&nbsp;called&nbsp;with&nbsp;one&nbsp;argument,&nbsp;x&nbsp;will&nbsp;be&nbsp;bound&nbsp;to&nbsp;the&nbsp;value&nbsp;of&nbsp;that&nbsp;<BR>
argument&nbsp;and&nbsp;y&nbsp;will&nbsp;be&nbsp;bound&nbsp;to&nbsp;nil;&nbsp;if&nbsp;it&nbsp;is&nbsp;called&nbsp;with&nbsp;two&nbsp;<BR>
arguments,&nbsp;x&nbsp;and&nbsp;y&nbsp;will&nbsp;be&nbsp;bound&nbsp;to&nbsp;the&nbsp;values&nbsp;of&nbsp;the&nbsp;first&nbsp;and&nbsp;second&nbsp;<BR>
argument,&nbsp;respectively.&nbsp;<BR>
&nbsp;<BR>
The&nbsp;function&nbsp;baaz&nbsp;has&nbsp;two&nbsp;optional&nbsp;arguments.&nbsp;It&nbsp;specifies&nbsp;a&nbsp;default&nbsp;<BR>
value&nbsp;for&nbsp;each&nbsp;of&nbsp;them:&nbsp;if&nbsp;the&nbsp;caller&nbsp;specifies&nbsp;only&nbsp;one&nbsp;argument,&nbsp;z&nbsp;<BR>
will&nbsp;be&nbsp;bound&nbsp;to&nbsp;10&nbsp;instead&nbsp;of&nbsp;to&nbsp;nil,&nbsp;and&nbsp;if&nbsp;the&nbsp;caller&nbsp;specifies&nbsp;no&nbsp;<BR>
arguments,&nbsp;x&nbsp;will&nbsp;be&nbsp;bound&nbsp;to&nbsp;3&nbsp;and&nbsp;z&nbsp;to&nbsp;10.&nbsp;<BR>
&nbsp;<BR>
You&nbsp;can&nbsp;make&nbsp;your&nbsp;function&nbsp;accept&nbsp;any&nbsp;number&nbsp;of&nbsp;arguments&nbsp;by&nbsp;ending&nbsp;its&nbsp;<BR>
argument&nbsp;list&nbsp;with&nbsp;an&nbsp;&amp;rest&nbsp;parameter.&nbsp;LISP&nbsp;will&nbsp;collect&nbsp;all&nbsp;arguments&nbsp;<BR>
not&nbsp;otherwise&nbsp;accounted&nbsp;for&nbsp;into&nbsp;a&nbsp;list&nbsp;and&nbsp;bind&nbsp;the&nbsp;&amp;rest&nbsp;parameter&nbsp;to&nbsp;<BR>
that&nbsp;list.&nbsp;So:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;foo&nbsp;(x&nbsp;&amp;rest&nbsp;y)&nbsp;y)&nbsp;</I><BR>
FOO&nbsp;<BR>
＞<I>&nbsp;(foo&nbsp;3)&nbsp;</I><BR>
NIL&nbsp;<BR>
＞<I>&nbsp;(foo&nbsp;4&nbsp;5&nbsp;6)&nbsp;</I><BR>
(5&nbsp;6)&nbsp;<BR>
&nbsp;<BR>
Finally,&nbsp;you&nbsp;can&nbsp;give&nbsp;your&nbsp;function&nbsp;another&nbsp;kind&nbsp;of&nbsp;optional&nbsp;argument&nbsp;<BR>
called&nbsp;a&nbsp;keyword&nbsp;argument.&nbsp;The&nbsp;caller&nbsp;can&nbsp;give&nbsp;these&nbsp;arguments&nbsp;in&nbsp;any&nbsp;<BR>
order,&nbsp;because&nbsp;they're&nbsp;labelled&nbsp;with&nbsp;keywords.&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;foo&nbsp;(&amp;key&nbsp;x&nbsp;y)&nbsp;(cons&nbsp;x&nbsp;y))&nbsp;</I><BR>
FOO&nbsp;<BR>
＞<I>&nbsp;(foo&nbsp;:x&nbsp;5&nbsp;:y&nbsp;3)&nbsp;</I><BR>
(5&nbsp;.&nbsp;3)&nbsp;<BR>
＞<I>&nbsp;(foo&nbsp;:y&nbsp;3&nbsp;:x&nbsp;5)&nbsp;</I><BR>
(5&nbsp;.&nbsp;3)&nbsp;<BR>
＞<I>&nbsp;(foo&nbsp;:y&nbsp;3)&nbsp;</I><BR>
(NIL&nbsp;.&nbsp;3)&nbsp;<BR>
＞<I>&nbsp;(foo)&nbsp;</I><BR>
(NIL)&nbsp;<BR>
&nbsp;<BR>
An&nbsp;&amp;key&nbsp;parameter&nbsp;can&nbsp;have&nbsp;a&nbsp;default&nbsp;value&nbsp;too:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(defun&nbsp;foo&nbsp;(&amp;key&nbsp;(x&nbsp;5))&nbsp;x)&nbsp;</I><BR>
FOO&nbsp;<BR>
＞<I>&nbsp;(foo&nbsp;:x&nbsp;7)&nbsp;</I><BR>
7&nbsp;<BR>
＞<I>&nbsp;(foo)&nbsp;</I><BR>
5&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Printing&nbsp;<BR>
&nbsp;<BR>
Some&nbsp;functions&nbsp;can&nbsp;cause&nbsp;output.&nbsp;The&nbsp;simplest&nbsp;one&nbsp;is&nbsp;print,&nbsp;which&nbsp;<BR>
prints&nbsp;its&nbsp;argument&nbsp;and&nbsp;then&nbsp;returns&nbsp;it.&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(print&nbsp;3)&nbsp;</I><BR>
3&nbsp;<BR>
3&nbsp;<BR>
&nbsp;<BR>
The&nbsp;first&nbsp;3&nbsp;above&nbsp;was&nbsp;printed,&nbsp;the&nbsp;second&nbsp;was&nbsp;returned.&nbsp;<BR>
&nbsp;<BR>
If&nbsp;you&nbsp;want&nbsp;more&nbsp;complicated&nbsp;output,&nbsp;you&nbsp;will&nbsp;need&nbsp;to&nbsp;use&nbsp;format.&nbsp;<BR>
Here's&nbsp;an&nbsp;example:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(format&nbsp;t&nbsp;&quot;An&nbsp;atom:&nbsp;~S~%and&nbsp;a&nbsp;list:&nbsp;~S~%and&nbsp;an&nbsp;integer:&nbsp;~D~%&quot;&nbsp;</I><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;nil&nbsp;(list&nbsp;5)&nbsp;6)&nbsp;<BR>
An&nbsp;atom:&nbsp;NIL&nbsp;<BR>
and&nbsp;a&nbsp;list:&nbsp;(5)&nbsp;<BR>
and&nbsp;an&nbsp;integer:&nbsp;6&nbsp;<BR>
&nbsp;<BR>
The&nbsp;first&nbsp;argument&nbsp;to&nbsp;format&nbsp;is&nbsp;either&nbsp;t,&nbsp;nil,&nbsp;or&nbsp;a&nbsp;stream.&nbsp;T&nbsp;specifies&nbsp;<BR>
output&nbsp;to&nbsp;the&nbsp;terminal.&nbsp;Nil&nbsp;means&nbsp;not&nbsp;to&nbsp;print&nbsp;anything&nbsp;but&nbsp;to&nbsp;return&nbsp;a&nbsp;<BR>
string&nbsp;containing&nbsp;the&nbsp;output&nbsp;instead.&nbsp;Streams&nbsp;are&nbsp;general&nbsp;places&nbsp;for&nbsp;<BR>
output&nbsp;to&nbsp;go:&nbsp;they&nbsp;can&nbsp;specify&nbsp;a&nbsp;file,&nbsp;or&nbsp;the&nbsp;terminal,&nbsp;or&nbsp;another&nbsp;<BR>
program.&nbsp;This&nbsp;handout&nbsp;will&nbsp;not&nbsp;describe&nbsp;streams&nbsp;in&nbsp;any&nbsp;further&nbsp;detail.&nbsp;<BR>
&nbsp;<BR>
The&nbsp;second&nbsp;argument&nbsp;is&nbsp;a&nbsp;formatting&nbsp;template,&nbsp;which&nbsp;is&nbsp;a&nbsp;string&nbsp;<BR>
optionally&nbsp;containing&nbsp;formatting&nbsp;directives.&nbsp;<BR>
&nbsp;<BR>
All&nbsp;remaining&nbsp;arguments&nbsp;may&nbsp;be&nbsp;referred&nbsp;to&nbsp;by&nbsp;the&nbsp;formatting&nbsp;<BR>
directives.&nbsp;LISP&nbsp;will&nbsp;replace&nbsp;the&nbsp;directives&nbsp;with&nbsp;some&nbsp;appropriate&nbsp;<BR>
characters&nbsp;based&nbsp;on&nbsp;the&nbsp;arguments&nbsp;to&nbsp;which&nbsp;they&nbsp;refer&nbsp;and&nbsp;then&nbsp;print&nbsp;<BR>
the&nbsp;resulting&nbsp;string.&nbsp;<BR>
&nbsp;<BR>
Format&nbsp;always&nbsp;returns&nbsp;nil&nbsp;unless&nbsp;its&nbsp;first&nbsp;argument&nbsp;is&nbsp;nil,&nbsp;in&nbsp;which&nbsp;<BR>
case&nbsp;it&nbsp;prints&nbsp;nothing&nbsp;and&nbsp;returns&nbsp;a&nbsp;string.&nbsp;<BR>
&nbsp;<BR>
There&nbsp;are&nbsp;three&nbsp;different&nbsp;directives&nbsp;in&nbsp;the&nbsp;above&nbsp;example:&nbsp;~S,&nbsp;~D,&nbsp;and&nbsp;<BR>
~%.&nbsp;The&nbsp;first&nbsp;one&nbsp;accepts&nbsp;any&nbsp;LISP&nbsp;object&nbsp;and&nbsp;is&nbsp;replaced&nbsp;by&nbsp;a&nbsp;printed&nbsp;<BR>
representation&nbsp;of&nbsp;that&nbsp;object&nbsp;(the&nbsp;same&nbsp;representation&nbsp;which&nbsp;is&nbsp;<BR>
produced&nbsp;by&nbsp;print).&nbsp;The&nbsp;second&nbsp;one&nbsp;accepts&nbsp;only&nbsp;integers.&nbsp;The&nbsp;third&nbsp;one&nbsp;<BR>
doesn't&nbsp;refer&nbsp;to&nbsp;an&nbsp;argument;&nbsp;it&nbsp;is&nbsp;always&nbsp;replaced&nbsp;by&nbsp;a&nbsp;carriage&nbsp;<BR>
return.&nbsp;<BR>
&nbsp;<BR>
Another&nbsp;useful&nbsp;directive&nbsp;is&nbsp;~~,&nbsp;which&nbsp;is&nbsp;replaced&nbsp;by&nbsp;a&nbsp;single&nbsp;~.&nbsp;<BR>
&nbsp;<BR>
Refer&nbsp;to&nbsp;a&nbsp;LISP&nbsp;manual&nbsp;for&nbsp;(many,&nbsp;many)&nbsp;additional&nbsp;formatting&nbsp;<BR>
directives.&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Forms&nbsp;and&nbsp;the&nbsp;Top-Level&nbsp;Loop&nbsp;<BR>
&nbsp;<BR>
The&nbsp;things&nbsp;which&nbsp;you&nbsp;type&nbsp;to&nbsp;the&nbsp;LISP&nbsp;interpreter&nbsp;are&nbsp;called&nbsp;forms;&nbsp;the&nbsp;<BR>
LISP&nbsp;interpreter&nbsp;repeatedly&nbsp;reads&nbsp;a&nbsp;form,&nbsp;evaluates&nbsp;it,&nbsp;and&nbsp;prints&nbsp;the&nbsp;<BR>
result.&nbsp;This&nbsp;procedure&nbsp;is&nbsp;called&nbsp;the&nbsp;read-eval-print&nbsp;loop.&nbsp;<BR>
&nbsp;<BR>
Some&nbsp;forms&nbsp;will&nbsp;cause&nbsp;errors.&nbsp;After&nbsp;an&nbsp;error,&nbsp;LISP&nbsp;will&nbsp;put&nbsp;you&nbsp;into&nbsp;<BR>
the&nbsp;debugger&nbsp;so&nbsp;you&nbsp;can&nbsp;try&nbsp;to&nbsp;figure&nbsp;out&nbsp;what&nbsp;caused&nbsp;the&nbsp;error.&nbsp;LISP&nbsp;<BR>
debuggers&nbsp;are&nbsp;all&nbsp;different;&nbsp;but&nbsp;most&nbsp;will&nbsp;respond&nbsp;to&nbsp;the&nbsp;command&nbsp;<BR>
&quot;help&quot;&nbsp;or&nbsp;&quot;:help&quot;&nbsp;by&nbsp;giving&nbsp;some&nbsp;form&nbsp;of&nbsp;help.&nbsp;<BR>
&nbsp;<BR>
In&nbsp;general,&nbsp;a&nbsp;form&nbsp;is&nbsp;either&nbsp;an&nbsp;atom&nbsp;(for&nbsp;example,&nbsp;a&nbsp;symbol,&nbsp;an&nbsp;<BR>
integer,&nbsp;or&nbsp;a&nbsp;string)&nbsp;or&nbsp;a&nbsp;list.&nbsp;If&nbsp;the&nbsp;form&nbsp;is&nbsp;an&nbsp;atom,&nbsp;LISP&nbsp;evaluates&nbsp;<BR>
it&nbsp;immediately.&nbsp;Symbols&nbsp;evaluate&nbsp;to&nbsp;their&nbsp;value;&nbsp;integers&nbsp;and&nbsp;strings&nbsp;<BR>
evaluate&nbsp;to&nbsp;themselves.&nbsp;If&nbsp;the&nbsp;form&nbsp;is&nbsp;a&nbsp;list,&nbsp;LISP&nbsp;treats&nbsp;its&nbsp;first&nbsp;<BR>
element&nbsp;as&nbsp;the&nbsp;name&nbsp;of&nbsp;a&nbsp;function;&nbsp;it&nbsp;evaluates&nbsp;the&nbsp;remaining&nbsp;elements&nbsp;<BR>
recursively,&nbsp;and&nbsp;then&nbsp;calls&nbsp;the&nbsp;function&nbsp;with&nbsp;the&nbsp;values&nbsp;of&nbsp;the&nbsp;<BR>
remaining&nbsp;elements&nbsp;as&nbsp;arguments.&nbsp;<BR>
&nbsp;<BR>
For&nbsp;example,&nbsp;if&nbsp;LISP&nbsp;sees&nbsp;the&nbsp;form&nbsp;(+&nbsp;3&nbsp;4),&nbsp;it&nbsp;treats&nbsp;+&nbsp;as&nbsp;the&nbsp;name&nbsp;of&nbsp;<BR>
a&nbsp;function.&nbsp;It&nbsp;then&nbsp;evaluates&nbsp;3&nbsp;to&nbsp;get&nbsp;3&nbsp;and&nbsp;4&nbsp;to&nbsp;get&nbsp;4;&nbsp;finally&nbsp;it&nbsp;<BR>
calls&nbsp;+&nbsp;with&nbsp;3&nbsp;and&nbsp;4&nbsp;as&nbsp;the&nbsp;arguments.&nbsp;The&nbsp;+&nbsp;function&nbsp;returns&nbsp;7,&nbsp;which&nbsp;<BR>
LISP&nbsp;prints.&nbsp;<BR>
&nbsp;<BR>
The&nbsp;top-level&nbsp;loop&nbsp;provides&nbsp;some&nbsp;other&nbsp;conveniences;&nbsp;one&nbsp;particularly&nbsp;<BR>
convenient&nbsp;convenience&nbsp;is&nbsp;the&nbsp;ability&nbsp;to&nbsp;talk&nbsp;about&nbsp;the&nbsp;results&nbsp;of&nbsp;<BR>