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📁 Tcl 语言的入门级图书
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<A NAME="top"><H1>Procedures</H1>


<P> At first glance, Tcl procedures are pretty standard.  Procedure invocations
have arguments that match up with parameters declared in procedure
implementations.  Namespaces for variables are different when procedures are
executing than before they are invoked.  Such local variable namespaces are
destroyed when their procedures finish executing.  Namespaces for procedures,
on the other hand, are global.  A procedure named <TT>p</TT> can be referenced
anyplace that the same Tcl interpreter controls.  (There is  one exception
to this described below in 
Action Families.)

<P> Beyond these common features, Tcl procedures have their own peculiarities.
They can be reimplemented on the fly.  The way they access and manipulate
values of nonlocal variables is unique.  These are topics you must
master before you can program well in Tcl.

<P> However, idiomatic Tcl/Tk programming involves more, it involves the
way you fit multiple actions into single procedures.  That topic, too,
is covered in this chapter &#150; your more complex scripts should take
advantage of it.

<P> Procedures are so important and the nuances of using them are so many
that the discussion of them continues with Chapter 9 and briefly
with Section 5.7.

<UL>
<LI> 
Procedures
<LI> 
Global and Local Variables
<LI> 
Passing Arguments by Reference
<LI> 
Default Values for Parameters
<LI> 
Reimplementing Procedures
<LI> 
Regional Variables
<LI> 
Action Families
<LI> 
An Example Action Family
<LI> 
Implementing Action Families in Earlier Versions of Tcl
<LI> 
Error Handling
<LI> 
<CITE>Procedures Defining Procedures</CITE>
<LI> 
Solutions to Exercises
</UL>
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<I>Jun 17, 1998</I>
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