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<h2>14. Macros
<a name="14. Macros"></a>
</h2>
<p style="margin-top: 1em"><font color="#000000">You can
define macros in <b>pic</b>, with up to 32 arguments (up to
16 on EBCDIC platforms). This is useful for diagrams with
repetitive parts. In conjunction with the scope rules for
block composites, it effectively gives you the ability to
write functions.</font></p>
<p style="margin-top: 1em"><font color="#000000">The syntax
is</font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><b>define</b>
<i>name</i> <b>{</b> <i>replacement text</i>
<b>}</b></font></p>
<p style="margin-top: 1em"><font color="#000000">This
defines <i>name</i> as a macro to be replaced by the
replacement text (not including the braces). The macro may
be called as</font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><i>name</i><b>(</b><i>arg1,
arg2, ... argn</i><b>)</b></font></p>
<p style="margin-top: 1em"><font color="#000000">The
arguments (if any) are substituted for tokens <b>$1</b>,
<b>$2</b> ... <b>$n</b> appearing in the replacement
text.</font></p>
<p style="margin-top: 1em"><font color="#000000">As an
example of macro use, consider this:</font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>.PS
<br>
# Plot a single jumper in a box, $1 is the on-off state.
<br>
define jumper { [ <br>
shrinkfactor = 0.8; <br>
Outer: box invis wid 0.45 ht 1;</small></font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>#
Count on end ] to reset these <br>
boxwid = Outer.wid * shrinkfactor / 2; <br>
boxht = Outer.ht * shrinkfactor / 2;</small></font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>box
fill (!$1) with .s at center of Outer; <br>
box fill ($1) with .n at center of Outer; <br>
] }</small></font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>#
Plot a block of six jumpers. <br>
define jumperblock { <br>
jumper($1); <br>
jumper($2); <br>
jumper($3); <br>
jumper($4); <br>
jumper($5); <br>
jumper($6);</small></font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>jwidth
= last [].Outer.wid; <br>
jheight = last [].Outer.ht;</small></font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>box
with .nw at 6th last [].nw wid 6*jwidth ht
jheight;</small></font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>#
Use {} to avoid changing position from last box draw. <br>
# This is necessary so move in any direction works as
expected <br>
{"Jumpers in state $1$2$3$4$5$6" at last box .s +
(0,-0.2);} <br>
}</small></font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>#
Sample macro invocations. <br>
jumperblock(1,1,0,0,1,0); <br>
move; <br>
jumperblock(1,0,1,0,1,1); <br>
.PE</small></font></p>
<p style="margin-top: 1em"><font color="#000000">It yields
the following:</font></p>
<p align="center" style="margin-top: 1em"><font color="#000000"><img src="img/pic44.png" alt="Image img/pic44.png"></font></p>
<p align="center" style="margin-top: 1em"><font color="#000000">Figure
14-1: Sample use of a macro</font></p>
<p style="margin-top: 1em"><font color="#000000">This macro
example illustrates how you can combine [], brace grouping,
and variable assignment to write true functions.</font></p>
<p style="margin-top: 1em"><font color="#000000">One detail
the example above does not illustrate is the fact that macro
argument parsing is not token-oriented. If you call
<b>jumper( 1 )</b>, the value of $1 is
<b>" 1 "</b>. You could even call
<b>jumper(big string)</b> to give $1 the value
<b>"big string"</b>.</font></p>
<p style="margin-top: 1em"><font color="#000000">If you
want to pass in a coordinate pair, you can avoid getting
tripped up by the comma by wrapping the pair in
parentheses.</font></p>
<p style="margin-top: 1em"><font color="#000000">Macros
persist through pictures. To undefine a macro, say
<b>undef</b> <i>name</i>; for example,</font></p>
<p style="margin-left:10%; margin-top: 1em"><font color="#000000">undef
jumper <br>
undef jumperblock</font></p>
<p style="margin-top: 1em"><font color="#000000">would
undefine the two macros in the jumper block
example.</font></p>
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