Artifact 5ce795542e6ee8bfd06154e34e78460211c48d95709d018fc5013532e9e8e566:

• Executable file r37/lisp/csl/html/r37_0065.html — part of check-in [f2fda60abd] at 2011-09-02 18:13:33 on branch master — Some historical releases purely for archival purposes

  git-svn-id: https://svn.code.sf.net/p/reduce-algebra/code/trunk/historical@1375 2bfe0521-f11c-4a00-b80e-6202646ff360 (user: arthurcnorman@users.sourceforge.net, size: 2281) [annotate] [blame] [check-ins using] [more...]

<A NAME=SETQ>

<TITLE>SETQ</TITLE></A>
<b><a href=r37_idx.html>INDEX</a></b><p><p>



<B>SETQ</B> _ _ _  _ _ _  _ _ _  _ _ _ <B>operator</B><P>
<P>
 
 <P>
<P>
The <em>setq</em> operator is an infix or prefix binary assignment operator. 
It is identical to <em>:=</em>. 
 <P> <H3> 
syntax: </H3>
<P>
<P>
<em>setq</em>(&lt;restricted\_expression&gt;,&lt;expression&gt;) or 
<P>
<P>
&lt;restricted\_expression&gt; <em>setq</em> &lt;expression&gt; 
<P>
<P>
<P>
&lt;restricted expression&gt; is ordinarily a single identifier, though 
simple expressions may be used (see Comments below). &lt;expression&gt; can 
be any valid REDUCE expression. If &lt;expression&gt; is a 
<A HREF=r37_0345.html>matrix</A> 
identifier, then &lt;restricted\_expression&gt; can be a matrix identifier 
(redimensioned if necessary), which has each element set to the 
corresponding elements of the identifier on the right-hand side. 
<P>
<P>
 <P> <H3> 
examples: </H3>
<P><PRE><TT>
setq(b,6); 

  B := 6 


c setq sin(x); 

  C := SIN(X) 


w + setq(c,x+3) + z; 

  W + X + Z + 3 


c; 

  X + 3 


setq(a1 + a2,25); 

  A1 + A2 := 25 


a1; 

  - (A2 - 25)

</TT></PRE><P>Embedding a <em>setq</em> statement in an expression has the side 
effect of making 
the assignment, as shown in the third example above. 
<P>
<P>
Assignments are generally done for identifiers, but may be done for simple 
expressions as well, subject to the following remarks: 
<P>
<P>
 _ _ _ (i) 
If the left-hand side is an identifier, an operator, or a power, the rule 
is added to the rule table. 
<P>
<P>
 _ _ _ (ii) 
If the operators <em>- + /</em> appear on the left-hand side, all but the first 

term of the expression is moved to the right-hand side. 
<P>
<P>
 _ _ _ (iii) 
If the operator <em>*</em> appears on the left-hand side, any constant terms are
 
moved to the right-hand side, but the symbolic factors remain. 
<P>
<P>
Be careful not to make a recursive <em>setq</em> assignment that is not 
controlled inside a loop statement. The process of resubstitution 
continues until you get a stack overflow message. <em>setq</em> can be used 
to attach functionality to operators, as the <em>:=</em> does. 
<P>
<P>
<P>