mirror of
https://github.com/RTimothyEdwards/magic.git
synced 2026-08-28 17:15:13 +02:00
Tim Edwards
a816da60f9
since all of the title images still had 8.2, and the title text still said 7.3 or 7.4, having not been updated for a long time.
117 lines
4.4 KiB
HTML
117 lines
4.4 KiB
HTML
<HTML>
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<HEAD>
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<STYLE type="text/css">
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H1 {color: black }
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H2 {color: maroon }
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</STYLE>
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</HEAD>
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<TITLE>Magic-8.3 Command Reference</TITLE>
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<BODY BACKGROUND=graphics/blpaper.gif>
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<H1> <IMG SRC=graphics/magic_title8_3.png ALT="Magic VLSI Layout Tool Version 8.3">
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<IMG SRC=graphics/magic_OGL_sm.gif ALIGN="top" ALT="*"> </H1>
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<H2>tag</H2>
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<HR>
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Register a tag callback command.
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<HR>
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<H3>Usage:</H3>
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<BLOCKQUOTE>
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<B>tag</B> <I>command_name</I> [<I>procedure</I>] <BR><BR>
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<BLOCKQUOTE>
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where <I>command_name</I> is the name of any <B>magic</B>
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command, and <I>procedure</I> is any valid Tcl procedure.
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</BLOCKQUOTE>
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</BLOCKQUOTE>
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<H3>Summary:</H3>
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<BLOCKQUOTE>
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The <B>tag</B> command is registers callback procedures to be
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executed after the indicated <B>magic</B> command has been
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executed. The primary use of the <B>tag</B> command is to
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register procedures that update the GUI window in response
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to commands that are typed on the command line or generated
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from macro calls. <P>
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In keeping with standard methods for Tcl callback functions,
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certain "escape sequences" beginning with the percent ("<B>%</B>")
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character are allowed to be embedded in the callback function
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<I>procedure</I>, and are substituted prior to execution, with
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the substitutions defined as follows:
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<BLOCKQUOTE>
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<DL>
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<DT> <B>%W</B>
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<DD> Substitute the Tk path of the layout window from which
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or in reference to which <I>command_name</I> was invoked.
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<DT> <B>%r</B>
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<DD> Substitute the previous Tcl result string, but do not reset
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the Tcl result of the execution of <I>procedure</I>.
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<DT> <B>%R</B>
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<DD> Substitute the previous Tcl result string and reset the Tcl
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result from the execution of <I>procedure</I> such that the
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the result of <I>command_name</I> becomes the result of
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<I>procedure</I>.
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<DT> <B>%</B>[<B>0</B>-<B>5</B>]
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<DD> Substitute the zeroth to fifth argument to the original command.
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<DT> <B>%%</B>
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<DD> Substitute a single percent character.
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<DT> <B>%</B><I>char</I>
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<DD> where <I>char</I> is any character not defined above: No action,
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print exactly as written.
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</DL>
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</BLOCKQUOTE>
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When a tag callback is used, the return value seen by the interpreter
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is the return value of the function <I>procedure</I>, not the return
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value of the tagged command <I>command_name</I>. The escape sequence
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<B>%R</B> can be used to force the result of <I>command_name</I> to
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become the result of <I>procedure</I> (unless <I>procedure</I>
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produces an error condition, in which case the error is returned).
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The escape sequence <I>%r</I> passes the result of <I>command_name</I>
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as an argument to the procedure, which may choose to return it as
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a result, or not. <P>
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If no <I>procedure</I> is present, then the <B>tag</B> command
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returns whatever procedure string is attached to the indicated
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<I>command_name</I>, if any. This can be used as a way to prevent
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infinite recursion inside a tag callback; for example,
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<BLOCKQUOTE>
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<B>set savetag [tag callback </B><I>command</I><B>]</B> <BR>
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<I>(procedure calls, which may include a call to </I>command<I>)</I> <BR>
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<B>tag</B> <I>command</I> <B>$savetag</B>
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</BLOCKQUOTE>
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Another way to avoid infinite recursion is to check the procedure
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depth from within the tag callback procedure using the Tcl command
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"<B>info level</B>", to avoid executing the callback procedure if
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the level is not zero. <P>
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Only one tag callback is allowed per command name. However, only
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one is needed as that procedure may call as many other procedures
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as it wants to.
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</BLOCKQUOTE>
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<H3>Implementation Notes:</H3>
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<BLOCKQUOTE>
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<B>tag</B> is implemented as a built-in command in <B>magic</B>,
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but only in the Tcl version.
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</BLOCKQUOTE>
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<P><IMG SRC=graphics/line1.gif><P>
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<TABLE BORDER=0>
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<TR>
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<TD> <A HREF=commands.html>Return to command index</A>
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</TR>
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</TABLE>
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<P><I>Last updated:</I> March 7, 2020 at 1:06pm <P>
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</BODY>
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</HTML>
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