Alessandro Bonazzi
8c43d5cf2f
Files correlati : cg0.exe cg0700a.msk cg0700b.msk cg3.exe cg4.exe Bug : Commento: Merge 1.0 libraries
56 lines
2.0 KiB
XML
56 lines
2.0 KiB
XML
<?xml version='1.0'?>
|
|
<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
|
|
"../dtd/4.1.2/docbookx.dtd">
|
|
<section id="dsssl.expr.loop"><title>Loops</title>
|
|
<para>
|
|
<indexterm><primary>for loop, DSSSL and</primary></indexterm>
|
|
<indexterm><primary>loops, implementing (DSSSL)</primary></indexterm>
|
|
<indexterm><primary>tail recursion (DSSSL)</primary></indexterm>
|
|
|
|
<acronym>DSSSL</acronym> doesn't have any construct that resembles the
|
|
for loop that occurs in most imperative languages like C
|
|
and Java. Instead, <acronym>DSSSL</acronym> employs a common trick in
|
|
functional languages for implementing a loop: tail recursion.
|
|
</para>
|
|
<para>
|
|
Loops in <acronym>DSSSL</acronym> use a special form of
|
|
<literal>let</literal>. This loop counts from 1 to 10:
|
|
<screen>
|
|
(let <co id="dl1"/>loopvar <co id="dl2"/>((count 1))
|
|
<co id="dl3"/>(if (> count 10)
|
|
<co id="dl4"/>#t
|
|
(<co id="dl5"/>loopvar <co id="dl6"/>(+ count 1))))</screen></para>
|
|
<calloutlist>
|
|
<callout arearefs="dl1">
|
|
<para>This variable controls the loop. It is declared without an
|
|
initial value, immediately after the <literal>let</literal>
|
|
operand.</para>
|
|
</callout>
|
|
<callout arearefs="dl2">
|
|
<para>
|
|
<indexterm><primary>variables (DSSSL)</primary>
|
|
<secondary>local, defining after loop variable</secondary></indexterm>
|
|
|
|
Any number of additional local variables can be defined after
|
|
the loop variable, just as they can in any other
|
|
<literal>let</literal> expression.</para>
|
|
</callout>
|
|
<callout arearefs="dl3">
|
|
<para>If you ever want the loop to end, you have to put some sort of a
|
|
test in it.</para>
|
|
</callout>
|
|
<callout arearefs="dl4">
|
|
<para>This is the value that will be returned.</para>
|
|
</callout>
|
|
<callout arearefs="dl5">
|
|
<para>Note that you iterate the loop by using the loop variable as if
|
|
it was a function name.</para>
|
|
</callout>
|
|
<callout arearefs="dl6">
|
|
<para>The arguments to this function are the values that
|
|
you want the local variables declared in <xref linkend="dl2"/> to have
|
|
in the next iteration.</para>
|
|
</callout>
|
|
</calloutlist>
|
|
</section>
|