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groff-doc-1.21-2.fc15.i686.rpm

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<h2>21. PIC Reference
<a name="21. PIC Reference"></a>
</h2>


<p style="margin-top: 1em"><font color="#000000">This is an
annotated grammar of <b>pic</b>.</font></p>

<h3>21.1. Lexical Items
<a name="21.1. Lexical Items"></a>
</h3>


<p style="margin-top: 1em"><font color="#000000">In
general, <b>pic</b> is a free-format, token-oriented
language that ignores whitespace outside strings. But
certain lines and contructs are specially interpreted at the
lexical level:</font></p>

<p style="margin-top: 1em"><font color="#000000">A comment
begins with <b>#</b> and continues to <b>\n</b> (comments
may also follow text in a line). A line beginning with a
period or backslash may be interpreted as text to be passed
through to the post-processor, depending on command-line
options. An end-of-line backslash is interpreted as a
request to continue the line; the backslash and following
newline are ignored.</font></p>


<p style="margin-left:10%; margin-top: 1em"><font color="#000000">Here
are the grammar terminals:</font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="6%">



<p style="margin-top: 1em"><font color="#000000"><small>INT</small></font></p> </td>
<td width="4%"></td>
<td width="38%">


<p style="margin-top: 1em"><font color="#000000">A positive
integer.</font></p> </td>
<td width="42%">
</td></tr>
</table>


<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>NUMBER</small></font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="8%"></td>
<td width="2%"></td>
<td width="80%">


<p><font color="#000000">A floating point numeric constant.
May contain a decimal point or be expressed in scientific
notation in the style of <i>printf</i>(3)&rsquo;s %e escape.
A trailing &lsquo;i&rsquo; or &lsquo;I&rsquo; (indicating
the unit &lsquo;inch&rsquo;) is ignored.</font></p></td></tr>
<tr valign="top" align="left">
<td width="10%"></td>
<td width="8%">



<p style="margin-top: 1em"><font color="#000000"><small>TEXT</small></font></p> </td>
<td width="2%"></td>
<td width="80%">


<p style="margin-top: 1em"><font color="#000000">A string
enclosed in double quotes. A double quote within
<small>TEXT</small> must be preceded by a backslash. Instead
of <small>TEXT</small> you can use</font></p></td></tr>
</table>

<pre style="margin-left:30%; margin-top: 1em">sprintf ( TEXT [, &lt;expr&gt; ...] )</pre>



<p style="margin-left:20%; margin-top: 1em"><font color="#000000">except
after the &lsquo;until&rsquo; and &lsquo;last&rsquo;
keywords, and after all ordinal keywords (&lsquo;th&rsquo;
and friends).</font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="16%">



<p style="margin-top: 1em"><font color="#000000"><small>VARIABLE</small></font></p> </td>
<td width="74%">
</td></tr>
</table>

<p style="margin-left:20%;"><font color="#000000">A string
starting with a character from the set [a-z], optionally
followed by one or more characters of the set [a-zA-Z0-9_].
(Values of variables are preserved across
pictures.)</font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="10%"></td>
<td width="10%">



<p style="margin-top: 1em"><font color="#000000"><small>LABEL</small></font></p> </td>
<td width="80%">


<p style="margin-top: 1em"><font color="#000000">A string
starting with a character from the set [A-Z], optionally
followed by one or more characters of the set
[a-zA-Z0-9_].</font></p> </td></tr>
</table>


<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>COMMAND-LINE</small></font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="80%">


<p><font color="#000000">A line starting with a command
character (&lsquo;.&rsquo; in groff mode, &lsquo;\&rsquo; in
TeX mode).</font></p></td></tr>
</table>


<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>BALANCED-TEXT</small></font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="80%">


<p><font color="#000000">A string either enclosed by
&lsquo;{&rsquo; and &lsquo;}&rsquo; or with <i>X</i> and
<i>X</i>, where <i>X</i> doesn&rsquo;t occur in the
string.</font></p> </td></tr>
</table>


<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>BALANCED-BODY</small></font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="80%">


<p><font color="#000000">Delimiters as in
<small>BALANCED-TEXT</small> ; the body is interpreted as
&lsquo;<b>&lang;command&rang;...</b>&rsquo;.</font></p> </td></tr>
</table>


<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>FILENAME</small></font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="80%">


<p><font color="#000000">The name of a file. This has the
same semantics as <small>TEXT</small> .</font></p></td></tr>
</table>


<p style="margin-left:10%; margin-top: 1em"><font color="#000000"><small>MACRONAME</small></font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="20%"></td>
<td width="50%">


<p><font color="#000000">Either <small>VARIABLE</small> or
<small>LABEL</small> .</font></p></td>
<td width="30%">
</td></tr>
</table>

<h3>21.2. Semi-Formal Grammar
<a name="21.2. Semi-Formal Grammar"></a>
</h3>


<p style="margin-top: 1em"><font color="#000000">Tokens not
enclosed in &lang;&rang; are literals, except:</font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="4%">



<p style="margin-top: 1em"><font color="#000000">1.</font></p> </td>
<td width="6%"></td>
<td width="90%">


<p style="margin-top: 1em"><font color="#000000"><b>\n</b>
is a newline.</font></p></td></tr>
<tr valign="top" align="left">
<td width="4%">



<p style="margin-top: 1em"><font color="#000000">2.</font></p> </td>
<td width="6%"></td>
<td width="90%">


<p style="margin-top: 1em"><font color="#000000">Three dots
is a suffix meaning &lsquo;replace with 0 or more
repetitions of the preceding element(s).</font></p></td></tr>
<tr valign="top" align="left">
<td width="4%">



<p style="margin-top: 1em"><font color="#000000">3.</font></p> </td>
<td width="6%"></td>
<td width="90%">


<p style="margin-top: 1em"><font color="#000000">An
enclosure in square brackets has its usual meaning of
&lsquo;this clause is optional&rsquo;.</font></p></td></tr>
<tr valign="top" align="left">
<td width="4%">



<p style="margin-top: 1em"><font color="#000000">4.</font></p> </td>
<td width="6%"></td>
<td width="90%">



<p style="margin-top: 1em"><font color="#000000">Square-bracket-enclosed
portions within tokens are optional. Thus,
&lsquo;h[eigh]t&rsquo; matches either &lsquo;height&rsquo;
or &lsquo;ht&rsquo;.</font></p></td></tr>
</table>

<p style="margin-top: 1em"><font color="#000000">If one of
these special tokens has to be referred to literally, it is
surrounded with single quotes.</font></p>

<p style="margin-top: 1em"><font color="#000000">The
top-level <b>pic</b> object is a picture.</font></p>

<pre style="margin-left:10%; margin-top: 1em">&lt;picture&gt; ::=
  .PS [NUMBER [NUMBER]]\n
  &lt;statement&gt; ...
  .PE \n</pre>


<p style="margin-top: 1em"><font color="#000000">The
arguments, if present, represent the width and height of the
picture, causing <b>pic</b> to attempt to scale it to the
given dimensions in inches. In no case, however, the X and
Y&nbsp;dimensions of the picture exceed the values of the
style variables <b>maxpswid</b> and <b>maxpsheight</b>
(which default to the normal 8.5i by 11i page
size).</font></p>

<p style="margin-top: 1em"><font color="#000000">If the
ending &lsquo;.PE&rsquo; is replaced by &lsquo;.PF&rsquo;,
the page vertical position is restored to its value at the
time &lsquo;.PS&rsquo; was encountered. Another alternate
form of invocation is &lsquo;.PS&nbsp;&lt;
<small>FILENAME</small> &rsquo;, which replaces the
&lsquo;.PS&rsquo; line with a file to be interpreted by
<b>pic</b> (but this feature is deprecated).</font></p>

<p style="margin-top: 1em"><font color="#000000">The
&lsquo;.PS&rsquo;, &lsquo;.PE&rsquo;, and &lsquo;.PF&rsquo;
macros to perform centering and scaling are normally
supplied by the post-processor.</font></p>

<p style="margin-top: 1em"><font color="#000000">In the
following, either &lsquo;|&rsquo; or a new line starts an
alternative.</font></p>
<pre style="margin-left:10%; margin-top: 1em">&lt;statement&gt; ::=
  &lt;command&gt; ;
  &lt;command&gt; \n

&lt;command&gt; ::=
  &lt;primitive&gt; [&lt;attribute&gt;]
  LABEL : [;] &lt;command&gt;
  LABEL : [;] &lt;command&gt; [&lt;position&gt;]
  { &lt;command&gt; ... }
  VARIABLE [:] = &lt;any-expr&gt;
  figname = MACRONAME
  up | down | left | right
  COMMAND-LINE
  command &lt;print-arg&gt; ...
  print &lt;print-arg&gt; ...
  sh BALANCED-TEXT
  copy FILENAME
  copy [FILENAME] thru MACRONAME [until TEXT]
  copy [FILENAME] thru BALANCED-BODY [until TEXT]
  for VARIABLE = &lt;expr&gt; to &lt;expr&gt; [by [*] &lt;expr&gt;] do BALANCED-BODY
  if &lt;any-expr&gt; then BALANCED-BODY [else BALANCED-BODY]
  reset [VARIABLE [[,] VARIABLE ...]]


&lt;print-arg&gt; ::=
  TEXT
  &lt;expr&gt;
  &lt;position&gt;</pre>


<p style="margin-top: 1em"><font color="#000000">The
current position and direction are saved on entry to a
&lsquo;{&nbsp;...&nbsp;}&rsquo; construction and restored on
exit from it.</font></p>

<p style="margin-top: 1em"><font color="#000000">Note that
in &lsquo;if&rsquo; constructions, newlines can only occur
in <small>BALANCED-BODY</small> . This means that</font></p>

<pre style="margin-left:10%; margin-top: 1em">if
{ ... }
else
{ ... }</pre>


<p style="margin-top: 1em"><font color="#000000">fails. You
have to use the braces on the same line as the
keywords:</font></p>

<pre style="margin-left:10%; margin-top: 1em">if {
...
} else {
...
}</pre>


<p style="margin-top: 1em"><font color="#000000">This
restriction doesn&rsquo;t hold for the body after the
&lsquo;do&rsquo; in a &lsquo;for&rsquo;
construction.</font></p>

<p style="margin-top: 1em"><font color="#000000">At the
beginning of each picture, &lsquo;figname&rsquo; is reset to
the vbox name &lsquo;graph&rsquo;; this command has only a
meaning in TeX mode. While the grammar rules allow digits
and the underscore in the value of &lsquo;figname&rsquo;,
TeX normally accepts uppercase and lowercase letters only as
box names (you have to use &lsquo;\csname&rsquo; if you
really need to circumvent this limitation).</font></p>
<pre style="margin-left:10%; margin-top: 1em">&lt;any-expr&gt; ::=
  &lt;expr&gt;
  &lt;text-expr&gt;
  &lt;any-expr&gt; &lt;logical-op&gt; &lt;any-expr&gt;
  ! &lt;any-expr&gt;

&lt;logical-op&gt; ::=
  == | != | &amp;&amp; | &rsquo;||&rsquo;

&lt;text-expr&gt; ::=
  TEXT == TEXT
  TEXT != TEXT</pre>

<p style="margin-top: 1em"><font color="#000000">Logical
operators are handled specially by <b>pic</b> since they can
deal with text strings also. <b>pic</b> uses
<i>strcmp</i>(3) to test for equality of strings; an empty
string is considered as &lsquo;false&rsquo; for
&lsquo;&amp;&amp;&rsquo; and &lsquo;||&rsquo;.</font></p>

<pre style="margin-left:10%; margin-top: 1em">&lt;primitive&gt; ::=
  box                   # closed object &mdash; rectangle
  circle                # closed object &mdash; circle
  ellipse               # closed object &mdash; ellipse
  arc                   # open object &mdash; quarter-circle
  line                  # open object &mdash; line
  arrow                 # open object &mdash; line with arrowhead
  spline                # open object &mdash; spline curve
  move
  TEXT TEXT ...         # text within invisible box
  plot &lt;expr&gt; TEXT      # formatted text
  &rsquo;[&rsquo; &lt;command&gt; ... &rsquo;]&rsquo;</pre>


<p style="margin-top: 1em"><font color="#000000">Drawn
objects within &lsquo;[&nbsp;...&nbsp;]&rsquo; are treated
as a single composite object with a rectangular shape (that
of the bounding box of all the elements). Variable and label
assignments within a block are local to the block. Current
direction of motion is restored to the value at start of
block upon exit. Position is <i>not</i> restored (unlike
&lsquo;{&nbsp;}&rsquo;); instead, the current position
becomes the exit position for the current direction on the
block&rsquo;s bounding box.</font></p>

<pre style="margin-left:10%; margin-top: 1em">&lt;attribute&gt; ::=
  h[eigh]t &lt;expr&gt;       # set height of closed figure
  wid[th] &lt;expr&gt;        # set width of closed figure
  rad[ius] &lt;expr&gt;       # set radius of circle/arc
  diam[eter] &lt;expr&gt;     # set diameter of circle/arc
  up [&lt;expr&gt;]           # move up
  down [&lt;expr&gt;]         # move down
  left [&lt;expr&gt;]         # move left
  right [&lt;expr&gt;]        # move right
  from &lt;position&gt;       # set from position of open figure
  to &lt;position&gt;         # set to position of open figure
  at &lt;position&gt;         # set center of open figure
  with &lt;path&gt;           # fix corner/named point at specified location
  with &lt;position&gt;       # fix position of object at specified location
  by &lt;expr-pair&gt;        # set object&rsquo;s attachment point
  then                  # sequential segment composition
  dotted [&lt;expr&gt;]       # set dotted line style
  dashed [&lt;expr&gt;]       # set dashed line style
  thick[ness] &lt;expr&gt;    # set thickness of lines
  chop [&lt;expr&gt;]         # chop end(s) of segment
  &rsquo;-&gt;&rsquo; | &rsquo;&lt;-&rsquo; | &rsquo;&lt;-&gt;&rsquo;   # decorate with arrows
  invis[ible]           # make primitive invisible
  solid                 # make closed figure solid
  fill[ed] [&lt;expr&gt;]     # set fill density for figure
  xscaled &lt;expr&gt;        # slant box into x direction
  yscaled &lt;expr&gt;        # slant box into y direction
  colo[u]r[ed] TEXT     # set fill and outline color for figure
  outline[d] TEXT       # set outline color for figure
  shaded TEXT           # set fill color for figure
  same                  # copy size of previous object
  cw | ccw              # set orientation of curves
  ljust | rjust         # adjust text horizontally
  above | below         # adjust text vertically
  aligned               # align parallel to object
  TEXT TEXT ...         # text within object
  &lt;expr&gt;                # motion in the current direction</pre>


<p style="margin-top: 1em"><font color="#000000">Missing
attributes are supplied from defaults; inappropriate ones
are silently ignored. For lines, splines, and arcs, height
and width refer to arrowhead size.</font></p>

<p style="margin-top: 1em"><font color="#000000">The
&lsquo;at&rsquo; primitive sets the center of the current
object. The &lsquo;with&rsquo; attribute fixes the specified
feature of the given object to a specified location. (Note
that &lsquo;with&rsquo; is incorrectly described in the
Kernighan paper.)</font></p>

<p style="margin-top: 1em"><font color="#000000">The
&lsquo;by&rsquo; primitive is not documented in the tutorial
portion of the Kernighan paper, and should probably be
considered unreliable.</font></p>

<p style="margin-top: 1em"><font color="#000000">The
primitive &lsquo;arrow&rsquo; is a synonym for
&lsquo;line&nbsp;-&gt;&rsquo;.</font></p>

<p style="margin-top: 1em"><font color="#000000">Text is
normally an attribute of some object, in which case
successive strings are vertically stacked and centered on
the object&rsquo;s center by default. Standalone text is
treated as though placed in an invisible box.</font></p>

<p style="margin-top: 1em"><font color="#000000">A text
item consists of a string or sprintf-expression, optionally
followed by positioning information. Text (or strings
specified with &lsquo;sprintf&rsquo;) may contain font
changes, size changes, and local motions, provided those
changes are undone before the end of the current item. Text
may also contain \-escapes denoting special characters. The
base font and specific set of escapes supported is
implementation dependent, but supported escapes always
include the following:</font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="16%">


<p style="margin-top: 1em"><font color="#000000">\fR,
\f1</font></p> </td>
<td width="84%">
</td></tr>
</table>

<p style="margin-left:10%;"><font color="#000000">Set Roman
style (the default)</font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="16%">


<p style="margin-top: 1em"><font color="#000000">\fI,
\f2</font></p> </td>
<td width="84%">
</td></tr>
</table>

<p style="margin-left:10%;"><font color="#000000">Set
Italic style</font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="16%">


<p style="margin-top: 1em"><font color="#000000">\fB,
\f3</font></p> </td>
<td width="84%">
</td></tr>
</table>

<p style="margin-left:10%;"><font color="#000000">Set Bold
style</font></p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="18%">



<p style="margin-top: 1em"><font color="#000000">\fP&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</font></p> </td>
<td width="82%">
</td></tr>
</table>

<p style="margin-left:10%;"><font color="#000000">Revert to
previous style; only works one level deep, does not
stack.</font></p>

<p style="margin-top: 1em"><font color="#000000">Color
names are dependent on the pic implementation, but in all
modern versions color names recognized by the X&nbsp;window
system are supported.</font></p>

<p style="margin-top: 1em"><font color="#000000">A position
is an (x,y) coordinate pair. There are lots of different
ways to specify positions:</font></p>
<pre style="margin-left:10%; margin-top: 1em">&lt;position&gt; ::=
  &lt;position-not-place&gt;
  &lt;place&gt;
  ( &lt;position&gt; )

&lt;position-not-place&gt; ::=
  &lt;expr-pair&gt;
  &lt;position&gt; + &lt;expr-pair&gt;
  &lt;position&gt; - &lt;expr-pair&gt;
  ( &lt;position&gt; , &lt;position&gt; )
  &lt;expr&gt; [of the way] between &lt;position&gt; and &lt;position&gt;
  &lt;expr&gt; &rsquo;&lt;&rsquo; &lt;position&gt; , &lt;position&gt; &rsquo;&gt;&rsquo;

&lt;expr-pair&gt; ::=
  &lt;expr&gt; , &lt;expr&gt;
  ( expr-pair )

&lt;place&gt; ::=
  &lt;label&gt;
  &lt;label&gt; &lt;corner&gt;
  &lt;corner&gt; [of] &lt;label&gt;
  Here

&lt;label&gt; ::=
  LABEL [. LABEL ...]
  &lt;nth-primitive&gt;

&lt;corner&gt; ::=
  .n | .e | .w | .s
  .ne | .se | .nw | .sw
  .c[enter] | .start | .end
  .t[op] | .b[ot[tom]] | .l[eft] | .r[ight]
  left | right | &lt;top-of&gt; | &lt;bottom-of&gt;
  &lt;north-of&gt; | &lt;south-of&gt; | &lt;east-of&gt; | &lt;west-of&gt;
  &lt;center-of&gt; | &lt;start-of&gt; | &lt;end-of&gt;
  upper left | lower left | upper right | lower right

&lt;<i>xxx</i>-of&gt; ::=
<i>  xxx</i>                   # followed by &lsquo;of&rsquo;

&lt;nth-primitive&gt; ::=
  &lt;ordinal&gt; &lt;object-type&gt;
  [&lt;ordinal&gt;] last &lt;object-type&gt;

&lt;ordinal&gt; ::=
  INT th
  INT st | INT nd | INT rd
  &lsquo; &lt;any-expr&gt; &rsquo;th


&lt;object-type&gt; ::=
  box
  circle
  ellipse
  arc
  line
  arrow
  spline
  &rsquo;[]&rsquo;
  TEXT</pre>


<p style="margin-top: 1em"><font color="#000000">As
Kernighan notes, &ldquo;since barbarisms like <b>1th</b> and
<b>3th</b> are barbaric, synonyms like <b>1st</b> and
<b>3rd</b> are accepted as well.&rdquo; Objects of a given
type are numbered from 1 upwards in order of declaration;
the <b>last</b> modifier counts backwards.</font></p>

<p style="margin-top: 1em"><font color="#000000">The
&ldquo;&rsquo;th&rdquo; form (which allows you to select a
previous object with an expression, as opposed to a numeric
literal) is not documented in DWB&rsquo;s
<i>pic</i>(1).</font></p>

<p style="margin-top: 1em"><font color="#000000">The
&lang;<i>xxx</i>-of&rang; rule is special: The lexical
parser checks whether <i>xxx</i> is followed by the token
&lsquo;of&rsquo; without eliminating it so that the grammar
parser can still see &lsquo;of&rsquo;. Valid examples of
specifying a place with corner and label are thus</font></p>

<pre style="margin-left:10%; margin-top: 1em">A .n
.n of A
.n A
north of A</pre>



<p style="margin-top: 1em"><font color="#000000">while</font></p>


<pre style="margin-left:10%; margin-top: 1em">north A
A north</pre>


<p style="margin-top: 1em"><font color="#000000">both cause
a syntax error. (DWB <b>pic</b> also allows the weird form
&lsquo;A&nbsp;north&nbsp;of&rsquo;.)</font></p>

<p style="margin-top: 1em"><font color="#000000">Here the
special rules for the &lsquo;with&rsquo; keyword using a
path:</font></p>
<pre style="margin-left:10%; margin-top: 1em">&lt;path&gt; ::=
  &lt;relative-path&gt;
  ( &lt;relative-path&gt; , &lt;relative-path&gt; )


&lt;relative-path&gt; ::=
  &lt;corner&gt;
  . LABEL [. LABEL ...] [&lt;corner&gt;]</pre>


<p style="margin-top: 1em"><font color="#000000">The
following style variables control output:</font></p>


<p align="center"><font color="#000000"><img src="img/pic51.png" alt="Image img/pic51.png"></font></p>

<p><font color="#000000">Any of these can be set by
assignment, or reset using the <b>reset</b> statement. Style
variables assigned within &lsquo;[&nbsp;]&rsquo; blocks are
restored to their beginning-of-block value on exit;
top-level assignments persist across pictures. Dimensions
are divided by <b>scale</b> on output.</font></p>

<p style="margin-top: 1em"><font color="#000000">All
<b>pic</b> expressions are evaluated in floating point;
units are always inches (a trailing &lsquo;i&rsquo; or
&lsquo;I&rsquo; is ignored). Expressions have the following
simple grammar, with semantics very similar to
C&nbsp;expressions:</font></p>
<pre style="margin-left:10%; margin-top: 1em">&lt;expr&gt; ::=
  VARIABLE
  NUMBER
  &lt;place&gt; &lt;place-attribute&gt;
  &lt;expr&gt; &lt;op&gt; &lt;expr&gt;
  - &lt;expr&gt;
  ( &lt;any-expr&gt; )
  ! &lt;expr&gt;
  &lt;func1&gt; ( &lt;any-expr&gt; )
  &lt;func2&gt; ( &lt;any-expr&gt; , &lt;any-expr&gt; )
  rand ( )

&lt;place-attribute&gt;
 .x | .y | .h[eigh]t | .wid[th] | .rad

&lt;op&gt; ::=
  + | - | * | / | % | ^ | &rsquo;&lt;&rsquo; | &rsquo;&gt;&rsquo; | &rsquo;&lt;=&rsquo; | &rsquo;&gt;=&rsquo;

&lt;func1&gt; ::=
  sin | cos | log | exp | sqrt | int | rand | srand

&lt;func2&gt; ::=
  atan2 | max | min</pre>

<p style="margin-top: 1em"><font color="#000000">Both
<b>exp</b> and <b>log</b> are base 10; <b>int</b> does
integer truncation; and <b>rand()</b> returns a random
number in [0-1).</font></p>

<p style="margin-top: 1em"><font color="#000000">There are
<b>define</b> and <b>undef</b> statements which are not part
of the grammar (they behave as pre-processor macros to the
language). These may be used to define
pseudo-functions.</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 $1, $2 ... $n
appearing in the replacement text. To undefine a macro, say
<b>undef</b> <i>name</i>, specifying the name to be
undefined.</font></p>
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