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<TITLE>LambdaMOO Programmer's Manual - Conditionals</TITLE>
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<H3><A NAME="SEC31" HREF="ProgrammersManual_toc.html#TOC31">Statements for Testing Conditions</A></H3>

<P>
The <SAMP>`if'</SAMP> statement allows you to decide whether or not to perform some
statements based on the value of an arbitrary expression:

</P>

<PRE>
if (<VAR>expression</VAR>)
  <VAR>statements</VAR>
endif
</PRE>

<P>
<VAR>Expression</VAR> is evaluated and, if it returns a true value, the statements
are executed in order; otherwise, nothing more is done.

</P>
<P>
One frequently wants to perform one set of statements if some condition is
true and some other set of statements otherwise.  The optional <SAMP>`else'</SAMP>
phrase in an <SAMP>`if'</SAMP> statement allows you to do this:

</P>

<PRE>
if (<VAR>expression</VAR>)
  <VAR>statements-1</VAR>
else
  <VAR>statements-2</VAR>
endif
</PRE>

<P>
This statement is executed just like the previous one, except that
<VAR>statements-1</VAR> are executed if <VAR>expression</VAR> returns a true value and
<VAR>statements-2</VAR> are executed otherwise.

</P>
<P>
Sometimes, one needs to test several conditions in a kind of nested
fashion:

</P>

<PRE>
if (<VAR>expression-1</VAR>)
  <VAR>statements-1</VAR>
else
  if (<VAR>expression-2</VAR>)
    <VAR>statements-2</VAR>
  else
    if (<VAR>expression-3</VAR>)
      <VAR>statements-3</VAR>
    else
      <VAR>statements-4</VAR>
    endif
  endif
endif
</PRE>

<P>
Such code can easily become tedious to write and difficult to read.  MOO
provides a somewhat simpler notation for such cases:

</P>

<PRE>
if (<VAR>expression-1</VAR>)
  <VAR>statements-1</VAR>
elseif (<VAR>expression-2</VAR>)
  <VAR>statements-2</VAR>
elseif (<VAR>expression-3</VAR>)
  <VAR>statements-3</VAR>
else
  <VAR>statements-4</VAR>
endif
</PRE>

<P>
Note that <SAMP>`elseif'</SAMP> is written as a single word, without any spaces.  This
simpler version has the very same meaning as the original: evaluate
<VAR>expression-i</VAR> for <VAR>i</VAR> equal to 1, 2, and 3, in turn, until one of
them returns a true value; then execute the <VAR>statements-i</VAR> associated with
that expression.  If none of the <VAR>expression-i</VAR> return a true value, then
execute <VAR>statements-4</VAR>.

</P>
<P>
Any number of <SAMP>`elseif'</SAMP> phrases can appear, each having this form:

</P>

<PRE>
elseif (<VAR>expression</VAR>) <VAR>statements</VAR>
</PRE>

<P>
The complete syntax of the <SAMP>`if'</SAMP> statement, therefore, is as follows:

</P>

<PRE>
if (<VAR>expression</VAR>)
  <VAR>statements</VAR>
<VAR>zero-or-more-elseif-phrases</VAR>
<VAR>an-optional-else-phrase</VAR>
endif
</PRE>

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