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Code Editor : pic-14.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="generator" content="groff -Thtml, see www.gnu.org">
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
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 h1 { text-align: center }
</style>
<title>pic-14.html</title>

</head>
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<h2>14. Macros
<a name="14. Macros"></a>
</h2>

You can
define macros in pic, 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.

The syntax
is

define
name { replacement text
}

This
defines name as a macro to be replaced by the
replacement text (not including the braces). The macro may
be called as

name(arg1,
arg2, ... argn)

The
arguments (if any) are substituted for tokens $1,
$2 ... $n appearing in the replacement
text.

As an
example of macro use, consider this:

.PS
 
# Plot a single jumper in a box, $1 is the on-off state.
 
define jumper { [ 
shrinkfactor = 0.8; 
Outer: box invis wid 0.45 ht 1;

#
Count on end ] to reset these 
boxwid = Outer.wid * shrinkfactor / 2; 
boxht = Outer.ht * shrinkfactor / 2;

box
fill (!$1) with .s at center of Outer; 
box fill ($1) with .n at center of Outer; 
] }

#
Plot a block of six jumpers. 
define jumperblock { 
jumper($1); 
jumper($2); 
jumper($3); 
jumper($4); 
jumper($5); 
jumper($6);

jwidth
= last [].Outer.wid; 
jheight = last [].Outer.ht;

box
with .nw at 6th last [].nw wid 6*jwidth ht
jheight;

#
Use {} to avoid changing position from last box draw. 
# This is necessary so move in any direction works as
expected 
{&quot;Jumpers in state $1$2$3$4$5$6&quot; at last box .s +
(0,-0.2);} 
}

#
Sample macro invocations. 
jumperblock(1,1,0,0,1,0); 
move; 
jumperblock(1,0,1,0,1,1); 
.PE

It yields
the following:

Figure
14-1: Sample use of a macro

This macro
example illustrates how you can combine [], brace grouping,
and variable assignment to write true functions.

One detail
the example above does not illustrate is the fact that macro
argument parsing is not token-oriented. If you call
jumper(&nbsp;1&nbsp;), the value of $1 is
&quot;&nbsp;1&nbsp;&quot;. You could even call
jumper(big&nbsp;string) to give $1 the value
&quot;big&nbsp;string&quot;.

If you
want to pass in a coordinate pair, you can avoid getting
tripped up by the comma by wrapping the pair in
parentheses.

Macros
persist through pictures. To undefine a macro, say
undef name; for example,

undef
jumper 
undef jumperblock

would
undefine the two macros in the jumper block
example.
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${this.title}

Code Editor : pic-14.html