00000004.htm

来自「一份很好的linux入门资料」· HTM 代码 · 共 1,027 行 · 第 1/5 页

＞<I>&nbsp;(aref&nbsp;*&nbsp;1&nbsp;1)&nbsp;</I><BR>
NIL&nbsp;<BR>
＞<I>&nbsp;(make-array&nbsp;4)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;1D&nbsp;arrays&nbsp;don't&nbsp;need&nbsp;the&nbsp;extra&nbsp;parens&nbsp;</I><BR>
#(NIL&nbsp;NIL&nbsp;NIL&nbsp;NIL)&nbsp;<BR>
&nbsp;<BR>
Array&nbsp;indices&nbsp;always&nbsp;start&nbsp;at&nbsp;0.&nbsp;<BR>
&nbsp;<BR>
See&nbsp;below&nbsp;for&nbsp;how&nbsp;to&nbsp;set&nbsp;the&nbsp;elements&nbsp;of&nbsp;an&nbsp;array.&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Strings&nbsp;<BR>
&nbsp;<BR>
A&nbsp;string&nbsp;is&nbsp;a&nbsp;sequence&nbsp;of&nbsp;characters&nbsp;between&nbsp;double&nbsp;quotes.&nbsp;LISP&nbsp;<BR>
represents&nbsp;a&nbsp;string&nbsp;as&nbsp;a&nbsp;variable-length&nbsp;array&nbsp;of&nbsp;characters.&nbsp;You&nbsp;can&nbsp;<BR>
write&nbsp;a&nbsp;string&nbsp;which&nbsp;contains&nbsp;a&nbsp;double&nbsp;quote&nbsp;by&nbsp;preceding&nbsp;the&nbsp;quote&nbsp;<BR>
with&nbsp;a&nbsp;backslash;&nbsp;a&nbsp;double&nbsp;backslash&nbsp;stands&nbsp;for&nbsp;a&nbsp;single&nbsp;backslash.&nbsp;For&nbsp;<BR>
example:&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot;abcd&quot;&nbsp;has&nbsp;4&nbsp;characters&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot;\&quot;&quot;&nbsp;has&nbsp;1&nbsp;character&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot;\\&quot;&nbsp;has&nbsp;1&nbsp;character&nbsp;<BR>
&nbsp;<BR>
Here&nbsp;are&nbsp;some&nbsp;functions&nbsp;for&nbsp;dealing&nbsp;with&nbsp;strings:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(concatenate&nbsp;'string&nbsp;&quot;abcd&quot;&nbsp;&quot;efg&quot;)&nbsp;</I><BR>
&quot;abcdefg&quot;&nbsp;<BR>
＞<I>&nbsp;(char&nbsp;&quot;abc&quot;&nbsp;1)&nbsp;</I><BR>
#\b&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;LISP&nbsp;writes&nbsp;characters&nbsp;preceded&nbsp;by&nbsp;#\&nbsp;<BR>
＞<I>&nbsp;(aref&nbsp;&quot;abc&quot;&nbsp;1)&nbsp;</I><BR>
#\b&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;remember,&nbsp;strings&nbsp;are&nbsp;really&nbsp;arrays&nbsp;<BR>
&nbsp;<BR>
The&nbsp;concatenate&nbsp;function&nbsp;can&nbsp;actually&nbsp;work&nbsp;with&nbsp;any&nbsp;type&nbsp;of&nbsp;sequence:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(concatenate&nbsp;'string&nbsp;'(#\a&nbsp;#\b)&nbsp;'(#\c))&nbsp;</I><BR>
&quot;abc&quot;&nbsp;<BR>
＞<I>&nbsp;(concatenate&nbsp;'list&nbsp;&quot;abc&quot;&nbsp;&quot;de&quot;)&nbsp;</I><BR>
(#\a&nbsp;#\b&nbsp;#\c&nbsp;#\d&nbsp;#\e)&nbsp;<BR>
＞<I>&nbsp;(concatenate&nbsp;'vector&nbsp;'#(3&nbsp;3&nbsp;3)&nbsp;'#(3&nbsp;3&nbsp;3))&nbsp;</I><BR>
#(3&nbsp;3&nbsp;3&nbsp;3&nbsp;3&nbsp;3)&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Structures&nbsp;<BR>
&nbsp;<BR>
LISP&nbsp;structures&nbsp;are&nbsp;analogous&nbsp;to&nbsp;C&nbsp;structs&nbsp;or&nbsp;Pascal&nbsp;records.&nbsp;Here&nbsp;is&nbsp;<BR>
an&nbsp;example:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(defstruct&nbsp;foo&nbsp;</I><BR>
&nbsp;&nbsp;&nbsp;&nbsp;bar&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;baaz&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;quux&nbsp;<BR>
&nbsp;&nbsp;)&nbsp;<BR>
FOO&nbsp;<BR>
&nbsp;<BR>
This&nbsp;example&nbsp;defines&nbsp;a&nbsp;data&nbsp;type&nbsp;called&nbsp;foo&nbsp;which&nbsp;is&nbsp;a&nbsp;structure&nbsp;<BR>
containing&nbsp;3&nbsp;fields.&nbsp;It&nbsp;also&nbsp;defines&nbsp;4&nbsp;functions&nbsp;which&nbsp;operate&nbsp;on&nbsp;this&nbsp;<BR>
data&nbsp;type:&nbsp;make-foo,&nbsp;foo-bar,&nbsp;foo-baaz,&nbsp;and&nbsp;foo-quux.&nbsp;The&nbsp;first&nbsp;one&nbsp;<BR>
makes&nbsp;a&nbsp;new&nbsp;object&nbsp;of&nbsp;type&nbsp;foo;&nbsp;the&nbsp;others&nbsp;access&nbsp;the&nbsp;fields&nbsp;of&nbsp;an&nbsp;<BR>
object&nbsp;of&nbsp;type&nbsp;foo.&nbsp;Here&nbsp;is&nbsp;how&nbsp;to&nbsp;use&nbsp;these&nbsp;functions:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(make-foo)&nbsp;</I><BR>
#s(FOO&nbsp;:BAR&nbsp;NIL&nbsp;:BAAZ&nbsp;NIL&nbsp;:QUUX&nbsp;NIL)&nbsp;<BR>
＞<I>&nbsp;(make-foo&nbsp;:baaz&nbsp;3)&nbsp;</I><BR>
#s(FOO&nbsp;:BAR&nbsp;NIL&nbsp;:BAAZ&nbsp;3&nbsp;:QUUX&nbsp;NIL)&nbsp;<BR>
＞<I>&nbsp;(foo-bar&nbsp;*)&nbsp;</I><BR>
NIL&nbsp;<BR>
＞<I>&nbsp;(foo-baaz&nbsp;**)&nbsp;</I><BR>
3&nbsp;<BR>
&nbsp;<BR>
The&nbsp;make-foo&nbsp;function&nbsp;can&nbsp;take&nbsp;a&nbsp;keyword&nbsp;argument&nbsp;for&nbsp;each&nbsp;of&nbsp;the&nbsp;<BR>
fields&nbsp;a&nbsp;structure&nbsp;of&nbsp;type&nbsp;foo&nbsp;can&nbsp;have.&nbsp;The&nbsp;field&nbsp;access&nbsp;functions&nbsp;<BR>
each&nbsp;take&nbsp;one&nbsp;argument,&nbsp;a&nbsp;structure&nbsp;of&nbsp;type&nbsp;foo,&nbsp;and&nbsp;return&nbsp;the&nbsp;<BR>
appropriate&nbsp;field.&nbsp;<BR>
&nbsp;<BR>
See&nbsp;below&nbsp;for&nbsp;how&nbsp;to&nbsp;set&nbsp;the&nbsp;fields&nbsp;of&nbsp;a&nbsp;structure.&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Setf&nbsp;<BR>
&nbsp;<BR>
Certain&nbsp;forms&nbsp;in&nbsp;LISP&nbsp;naturally&nbsp;define&nbsp;a&nbsp;memory&nbsp;location.&nbsp;For&nbsp;example,&nbsp;<BR>
if&nbsp;the&nbsp;value&nbsp;of&nbsp;x&nbsp;is&nbsp;a&nbsp;structure&nbsp;of&nbsp;type&nbsp;foo,&nbsp;then&nbsp;(foo-bar&nbsp;x)&nbsp;defines&nbsp;<BR>
the&nbsp;bar&nbsp;field&nbsp;of&nbsp;the&nbsp;value&nbsp;of&nbsp;x.&nbsp;Or,&nbsp;if&nbsp;the&nbsp;value&nbsp;of&nbsp;y&nbsp;is&nbsp;a&nbsp;one-&nbsp;<BR>
dimensional&nbsp;array,&nbsp;(aref&nbsp;y&nbsp;2)&nbsp;defines&nbsp;the&nbsp;third&nbsp;element&nbsp;of&nbsp;y.&nbsp;<BR>
&nbsp;<BR>
The&nbsp;setf&nbsp;special&nbsp;form&nbsp;uses&nbsp;its&nbsp;first&nbsp;argument&nbsp;to&nbsp;define&nbsp;a&nbsp;place&nbsp;in&nbsp;<BR>
memory,&nbsp;evaluates&nbsp;its&nbsp;second&nbsp;argument,&nbsp;and&nbsp;stores&nbsp;the&nbsp;resulting&nbsp;value&nbsp;<BR>
in&nbsp;the&nbsp;resulting&nbsp;memory&nbsp;location.&nbsp;For&nbsp;example,&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(setq&nbsp;a&nbsp;(make-array&nbsp;3))&nbsp;</I><BR>
#(NIL&nbsp;NIL&nbsp;NIL)&nbsp;<BR>
＞<I>&nbsp;(aref&nbsp;a&nbsp;1)&nbsp;</I><BR>
NIL&nbsp;<BR>
＞<I>&nbsp;(setf&nbsp;(aref&nbsp;a&nbsp;1)&nbsp;3)&nbsp;</I><BR>
3&nbsp;<BR>
＞<I>&nbsp;a&nbsp;</I><BR>
#(NIL&nbsp;3&nbsp;NIL)&nbsp;<BR>
＞<I>&nbsp;(aref&nbsp;a&nbsp;1)&nbsp;</I><BR>
3&nbsp;<BR>
＞<I>&nbsp;(defstruct&nbsp;foo&nbsp;bar)&nbsp;</I><BR>
FOO&nbsp;<BR>
＞<I>&nbsp;(setq&nbsp;a&nbsp;(make-foo))&nbsp;</I><BR>
#s(FOO&nbsp;:BAR&nbsp;NIL)&nbsp;<BR>
＞<I>&nbsp;(foo-bar&nbsp;a)&nbsp;</I><BR>
NIL&nbsp;<BR>
＞<I>&nbsp;(setf&nbsp;(foo-bar&nbsp;a)&nbsp;3)&nbsp;</I><BR>
3&nbsp;<BR>
＞<I>&nbsp;a&nbsp;</I><BR>
#s(FOO&nbsp;:BAR&nbsp;3)&nbsp;<BR>
＞<I>&nbsp;(foo-bar&nbsp;a)&nbsp;</I><BR>
3&nbsp;<BR>
&nbsp;<BR>
Setf&nbsp;is&nbsp;the&nbsp;only&nbsp;way&nbsp;to&nbsp;set&nbsp;the&nbsp;fields&nbsp;of&nbsp;a&nbsp;structure&nbsp;or&nbsp;the&nbsp;elements&nbsp;<BR>
of&nbsp;an&nbsp;array.&nbsp;<BR>
&nbsp;<BR>
Here&nbsp;are&nbsp;some&nbsp;more&nbsp;examples&nbsp;of&nbsp;setf&nbsp;and&nbsp;related&nbsp;functions.&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(setf&nbsp;a&nbsp;(make-array&nbsp;1))&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;setf&nbsp;on&nbsp;a&nbsp;variable&nbsp;is&nbsp;equivalent&nbsp;to&nbsp;setq&nbsp;</I><BR>
#(NIL)&nbsp;<BR>
＞<I>&nbsp;(push&nbsp;5&nbsp;(aref&nbsp;a&nbsp;1))&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;push&nbsp;can&nbsp;act&nbsp;like&nbsp;setf&nbsp;</I><BR>
(5)&nbsp;<BR>
＞<I>&nbsp;(pop&nbsp;(aref&nbsp;a&nbsp;1))&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;so&nbsp;can&nbsp;pop&nbsp;</I><BR>
5&nbsp;<BR>
＞<I>&nbsp;(setf&nbsp;(aref&nbsp;a&nbsp;1)&nbsp;5)&nbsp;</I><BR>
5&nbsp;<BR>
＞<I>&nbsp;(incf&nbsp;(aref&nbsp;a&nbsp;1))&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;incf&nbsp;reads&nbsp;from&nbsp;a&nbsp;place,&nbsp;increments,&nbsp;</I><BR>
6&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;;and&nbsp;writes&nbsp;back&nbsp;<BR>
＞<I>&nbsp;(aref&nbsp;a&nbsp;1)&nbsp;</I><BR>
6&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Booleans&nbsp;and&nbsp;Conditionals&nbsp;<BR>
&nbsp;<BR>
LISP&nbsp;uses&nbsp;the&nbsp;self-evaluating&nbsp;symbol&nbsp;nil&nbsp;to&nbsp;mean&nbsp;false.&nbsp;Anything&nbsp;other&nbsp;<BR>
than&nbsp;nil&nbsp;means&nbsp;true.&nbsp;Unless&nbsp;we&nbsp;have&nbsp;a&nbsp;reason&nbsp;not&nbsp;to,&nbsp;we&nbsp;usually&nbsp;use&nbsp;the&nbsp;<BR>
self-evaluating&nbsp;symbol&nbsp;t&nbsp;to&nbsp;stand&nbsp;for&nbsp;true.&nbsp;<BR>
&nbsp;<BR>
LISP&nbsp;provides&nbsp;a&nbsp;standard&nbsp;set&nbsp;of&nbsp;logical&nbsp;functions,&nbsp;for&nbsp;example&nbsp;and,&nbsp;or,&nbsp;<BR>
and&nbsp;not.&nbsp;The&nbsp;and&nbsp;and&nbsp;or&nbsp;connectives&nbsp;are&nbsp;short-circuiting:&nbsp;and&nbsp;will&nbsp;not&nbsp;<BR>
evaluate&nbsp;any&nbsp;arguments&nbsp;to&nbsp;the&nbsp;right&nbsp;of&nbsp;the&nbsp;first&nbsp;one&nbsp;which&nbsp;evaluates&nbsp;to&nbsp;<BR>
nil,&nbsp;while&nbsp;or&nbsp;will&nbsp;not&nbsp;evaluate&nbsp;any&nbsp;arguments&nbsp;to&nbsp;the&nbsp;right&nbsp;of&nbsp;the&nbsp;first&nbsp;<BR>
one&nbsp;which&nbsp;evaluates&nbsp;to&nbsp;t.&nbsp;<BR>
&nbsp;<BR>
LISP&nbsp;also&nbsp;provides&nbsp;several&nbsp;special&nbsp;forms&nbsp;for&nbsp;conditional&nbsp;execution.&nbsp;The&nbsp;<BR>
simplest&nbsp;of&nbsp;these&nbsp;is&nbsp;if.&nbsp;The&nbsp;first&nbsp;argument&nbsp;of&nbsp;if&nbsp;determines&nbsp;whether&nbsp;<BR>
the&nbsp;second&nbsp;or&nbsp;third&nbsp;argument&nbsp;will&nbsp;be&nbsp;executed:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(if&nbsp;t&nbsp;5&nbsp;6)&nbsp;</I><BR>
5&nbsp;<BR>
＞<I>&nbsp;(if&nbsp;nil&nbsp;5&nbsp;6)&nbsp;</I><BR>
6&nbsp;<BR>
＞<I>&nbsp;(if&nbsp;4&nbsp;5&nbsp;6)&nbsp;</I><BR>
5&nbsp;<BR>
&nbsp;<BR>
If&nbsp;you&nbsp;need&nbsp;to&nbsp;put&nbsp;more&nbsp;than&nbsp;one&nbsp;statement&nbsp;in&nbsp;the&nbsp;then&nbsp;or&nbsp;else&nbsp;clause&nbsp;<BR>
of&nbsp;an&nbsp;if&nbsp;statement,&nbsp;you&nbsp;can&nbsp;use&nbsp;the&nbsp;progn&nbsp;special&nbsp;form.&nbsp;Progn&nbsp;executes&nbsp;<BR>
each&nbsp;statement&nbsp;in&nbsp;its&nbsp;body,&nbsp;then&nbsp;returns&nbsp;the&nbsp;value&nbsp;of&nbsp;the&nbsp;final&nbsp;one.&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(setq&nbsp;a&nbsp;7)&nbsp;</I><BR>
7&nbsp;<BR>
＞<I>&nbsp;(setq&nbsp;b&nbsp;0)&nbsp;</I><BR>
0&nbsp;<BR>
＞<I>&nbsp;(setq&nbsp;c&nbsp;5)&nbsp;</I><BR>
5&nbsp;<BR>
＞<I>&nbsp;(if&nbsp;(&gt;&nbsp;a&nbsp;5)&nbsp;</I><BR>
&nbsp;&nbsp;&nbsp;&nbsp;(progn&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(setq&nbsp;a&nbsp;(+&nbsp;b&nbsp;7))&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(setq&nbsp;b&nbsp;(+&nbsp;c&nbsp;8)))&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;(setq&nbsp;b&nbsp;4)&nbsp;<BR>
&nbsp;&nbsp;)&nbsp;<BR>
13&nbsp;<BR>
&nbsp;<BR>
An&nbsp;if&nbsp;statement&nbsp;which&nbsp;lacks&nbsp;either&nbsp;a&nbsp;then&nbsp;or&nbsp;an&nbsp;else&nbsp;clause&nbsp;can&nbsp;be&nbsp;<BR>
written&nbsp;using&nbsp;the&nbsp;when&nbsp;or&nbsp;unless&nbsp;special&nbsp;form:&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(when&nbsp;t&nbsp;3)&nbsp;</I><BR>
3&nbsp;<BR>
＞<I>&nbsp;(when&nbsp;nil&nbsp;3)&nbsp;</I><BR>
NIL&nbsp;<BR>
＞<I>&nbsp;(unless&nbsp;t&nbsp;3)&nbsp;</I><BR>
NIL&nbsp;<BR>
＞<I>&nbsp;(unless&nbsp;nil&nbsp;3)&nbsp;</I><BR>
3&nbsp;<BR>
&nbsp;<BR>
When&nbsp;and&nbsp;unless,&nbsp;unlike&nbsp;if,&nbsp;allow&nbsp;any&nbsp;number&nbsp;of&nbsp;statements&nbsp;in&nbsp;their&nbsp;<BR>
bodies.&nbsp;(Eg,&nbsp;(when&nbsp;x&nbsp;a&nbsp;b&nbsp;c)&nbsp;is&nbsp;equivalent&nbsp;to&nbsp;(if&nbsp;x&nbsp;(progn&nbsp;a&nbsp;b&nbsp;c)).)&nbsp;<BR>
&nbsp;<BR>
＞<I>&nbsp;(when&nbsp;t&nbsp;</I><BR>
&nbsp;&nbsp;&nbsp;&nbsp;(setq&nbsp;a&nbsp;5)&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;(+&nbsp;a&nbsp;6)&nbsp;<BR>
&nbsp;&nbsp;)&nbsp;<BR>
11&nbsp;<BR>
&nbsp;<BR>
More&nbsp;complicated&nbsp;conditionals&nbsp;can&nbsp;be&nbsp;defined&nbsp;using&nbsp;the&nbsp;cond&nbsp;special&nbsp;<BR>
form,&nbsp;which&nbsp;is&nbsp;equivalent&nbsp;to&nbsp;an&nbsp;if&nbsp;...&nbsp;else&nbsp;if&nbsp;...&nbsp;fi&nbsp;construction.&nbsp;<BR>
&nbsp;<BR>
A&nbsp;cond&nbsp;consists&nbsp;of&nbsp;the&nbsp;symbol&nbsp;cond&nbsp;followed&nbsp;by&nbsp;a&nbsp;number&nbsp;of&nbsp;cond&nbsp;<BR>
clauses,&nbsp;each&nbsp;of&nbsp;which&nbsp;is&nbsp;a&nbsp;list.&nbsp;The&nbsp;first&nbsp;element&nbsp;of&nbsp;a&nbsp;cond&nbsp;clause&nbsp;is&nbsp;<BR>
the&nbsp;condition;&nbsp;the&nbsp;remaining&nbsp;elements&nbsp;(if&nbsp;any)&nbsp;are&nbsp;the&nbsp;action.&nbsp;The&nbsp;cond&nbsp;<BR>
form&nbsp;finds&nbsp;the&nbsp;first&nbsp;clause&nbsp;whose&nbsp;condition&nbsp;evaluates&nbsp;to&nbsp;true&nbsp;(ie,&nbsp;<BR>
doesn't&nbsp;evaluate&nbsp;to&nbsp;nil);&nbsp;it&nbsp;then&nbsp;executes&nbsp;the&nbsp;corresponding&nbsp;action&nbsp;and&nbsp;<BR>
returns&nbsp;the&nbsp;resulting&nbsp;value.&nbsp;None&nbsp;of&nbsp;the&nbsp;remaining&nbsp;conditions&nbsp;are&nbsp;<BR>
evaluated;&nbsp;nor&nbsp;are&nbsp;any&nbsp;actions&nbsp;except&nbsp;the&nbsp;one&nbsp;corresponding&nbsp;to&nbsp;the&nbsp;<BR>
selected&nbsp;condition.&nbsp;For&nbsp;example:&nbsp;<BR>