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control construct docs added

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[SVN r12734]
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Jaakko Järvi
2002-02-05 22:26:30 +00:00
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is granted, provided this copyright notice appears in all
copies, and a notice that the code was modified is included
with the copyright notice.
</p></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt>1. <a href="#introduction">In a nutshell</a></dt><dt>2. <a href="#sect:getting_started">Getting Started</a></dt><dd><dl><dt>2.1. <a href="#id2732612">Installing the library</a></dt></dl></dd><dt>3. <a href="#id2732964">Introduction</a></dt><dd><dl><dt>3.1. <a href="#id2732972">Motivation</a></dt><dt>3.2. <a href="#id2733662">Introduction to lambda expressions</a></dt></dl></dd><dt>4. <a href="#sect:using_library">Using the library</a></dt><dd><dl><dt>4.1. <a href="#sect:introductory_examples">Examples</a></dt><dt>4.2. <a href="#sect:parameter_and_return_types">Parameter and return types of lambda functors</a></dt><dt>4.3. <a href="#sect:actual_arguments_to_lambda_functors">About actual arguments to lambda functors</a></dt><dt>4.4. <a href="#sect:storing_bound_arguments">Storing bound arguments in lambda functions</a></dt></dl></dd><dt>5. <a href="#sect:lambda_expressions_in_details">Lambda expressions in details</a></dt><dd><dl><dt>5.1. <a href="#sect:placeholders">Placeholders</a></dt><dt>5.2. <a href="#sect:operator_expressions">Operator expressions</a></dt><dt>5.3. <a href="#bind_expressions">Bind expressions</a></dt><dt>5.4. <a href="#sect:overriding_deduced_return_value">Overriding the deduced return value</a></dt><dt>5.5. <a href="#sect:extending_return_type_system">Extending return type deduction system</a></dt><dt>5.6. <a href="#sect:delaying_constants_and_variables">Delaying constants and variables</a></dt><dt>5.7. <a href="#control_expressions">Control expressions</a></dt><dt>5.8. <a href="#id2794275">Exceptions</a></dt><dt>5.9. <a href="#construction_and_destruction">Construction and destruction</a></dt><dt>5.10. <a href="#id2794309">Special lambda expressions</a></dt></dl></dd><dt>6. <a href="#id2794352">Contributors</a></dt></dl></div><div class="simplesect"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2725492"></a>NOTE!</h2></div></div>
</p></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt>1. <a href="#introduction">In a nutshell</a></dt><dt>2. <a href="#sect:getting_started">Getting Started</a></dt><dd><dl><dt>2.1. <a href="#id2732612">Installing the library</a></dt></dl></dd><dt>3. <a href="#id2732964">Introduction</a></dt><dd><dl><dt>3.1. <a href="#id2732972">Motivation</a></dt><dt>3.2. <a href="#id2733662">Introduction to lambda expressions</a></dt></dl></dd><dt>4. <a href="#sect:using_library">Using the library</a></dt><dd><dl><dt>4.1. <a href="#sect:introductory_examples">Examples</a></dt><dt>4.2. <a href="#sect:parameter_and_return_types">Parameter and return types of lambda functors</a></dt><dt>4.3. <a href="#sect:actual_arguments_to_lambda_functors">About actual arguments to lambda functors</a></dt><dt>4.4. <a href="#sect:storing_bound_arguments">Storing bound arguments in lambda functions</a></dt></dl></dd><dt>5. <a href="#sect:lambda_expressions_in_details">Lambda expressions in details</a></dt><dd><dl><dt>5.1. <a href="#sect:placeholders">Placeholders</a></dt><dt>5.2. <a href="#sect:operator_expressions">Operator expressions</a></dt><dt>5.3. <a href="#bind_expressions">Bind expressions</a></dt><dt>5.4. <a href="#sect:overriding_deduced_return_value">Overriding the deduced return value</a></dt><dt>5.5. <a href="#sect:extending_return_type_system">Extending return type deduction system</a></dt><dt>5.6. <a href="#sect:delaying_constants_and_variables">Delaying constants and variables</a></dt><dt>5.7. <a href="#control_expressions">Control expressions</a></dt><dt>5.8. <a href="#id2794532">Exceptions</a></dt><dt>5.9. <a href="#construction_and_destruction">Construction and destruction</a></dt><dt>5.10. <a href="#id2794555">Special lambda expressions</a></dt></dl></dd><dt>6. <a href="#id2794599">Contributors</a></dt></dl></div><div class="simplesect"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2725492"></a>NOTE!</h2></div></div>
At the moment, the documentation is a draft. Exceptions, control constructs, advanced bind expressions (nesting binds etc.), constructor and destructor calls and a few other things are not documented yet.
@@ -926,9 +926,75 @@ This does not hold for compound assignment operators <tt>+=</tt>, <tt>-=</tt> et
Nevertheless, it is perfectly ok to delay the left operand explicitly.
For example, <tt>i += _1</tt> is equivalent to <tt>var(i) += _1</tt>.
</p></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="control_expressions"></a>5.7. Control expressions</h3></div></div><p>
BLL defines several functions to create lambda functors for control expressions.
They all take lambda functors as parameters and return <tt>void</tt>.
</p></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2794275"></a>5.8. Exceptions</h3></div></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="construction_and_destruction"></a>5.9. Construction and destruction</h3></div></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2794309"></a>5.10. Special lambda expressions</h3></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794317"></a>5.10.1. Protect</h4></div></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794325"></a>5.10.2. Const_parameters</h4></div></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794334"></a>5.10.3. Break_const</h4></div></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794342"></a>5.10.4. Unlambda</h4></div></div></div></div></div><div class="section"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2794352"></a>6. Contributors</h2></div></div>
BLL defines several functions to create lambda functors that represent control constructs.
They all take lambda functors as parameters and return <tt>void</tt>.
To start with an example, the following code outputs all even elements of some container <tt>a</tt>:
<pre class="programlisting">
for_each(a.begin(), a.end(),
if_then(_1 % 2 == 0, cout &lt;&lt; _1));
</pre>
</p><p>
The BLL supports the following function templates for control structures:
<pre class="programlisting">
if_then(condition, then_part)
if_then_else(condition, then_part, else_part)
while_loop(condition, body)
while_loop(condition) // no body case
do_while_loop(condition, body)
do_while_loop(condition) // no body case
for_loop(init, condition, increment, body)
for_loop(init, condition, increment) // no body case
switch_statement(...)
</pre>
</p><p>
Delayed variables tend to be commonplace in control lambda expressions.
For instance, here we use the <tt>var</tt> function to turn the arguments of <tt>for_loop</tt> into lambda expressions.
The effect of the code is to add 1 to each element of a two-dimensional array:
<pre class="programlisting">
int a[5][10]; int i;
for_each(a, a+5,
for_loop(var(i)=0, var(i)&lt;10, ++var(i),
_1[var(i)] += 1));
</pre>
As explained in <a href="#sect:delaying_constants_and_variables" title="5.6. Delaying constants and variables">Section 5.6</a>, we can avoid the repeated use of wrapping of <tt>var</tt> if we define it beforehand:
<pre class="programlisting">
int i;
var_type&lt;int&gt;::type vi(var(i));
for_each(a, a+5,
for_loop(vi=0, vi&lt;10, ++vi, _1[vi] += 6));
</pre>
</p><div class="section"><div class="titlepage"><div><h4 class="title"><a name="sect:switch_statement"></a>5.7.1. Switch statement</h4></div></div></div><p>
The lambda expressions for <tt>switch</tt> control structures are more complex since the number of cases may vary.
The general form of a switch lambda expression is:
<pre class="programlisting">
switch_statement(<i><tt>condition</tt></i>,
case_statement&lt;<i><tt>label</tt></i>&gt;(<i><tt>lambda expression</tt></i>),
case_statement&lt;<i><tt>label</tt></i>&gt;(<i><tt>lambda expression</tt></i>),
...
default_statement(<i><tt>lambda expression</tt></i>)
)
</pre>
The <tt><i><tt>condition</tt></i></tt> argument must be a lambda expression that creates a lambda functor with an integral return type.
The different cases are created with the <tt>case_statement</tt> functions, and the optional default case with the <tt>default_statement</tt> function.
The case labels are given as explicitly specified template arguments to <tt>case_statement functions</tt> and
<tt>break</tt> statements are implicitly part of each case.
For example, <tt>case_statement&lt;1&gt;(a)</tt>, where <tt>a</tt> is some lambda functor, generates the code:
<pre class="programlisting">case 1:
evaluate lambda functor a;
break;
</pre>
We have specialized the <tt>switch_statement</tt> function for up to 9 case statements.
</p></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2794532"></a>5.8. Exceptions</h3></div></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="construction_and_destruction"></a>5.9. Construction and destruction</h3></div></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2794555"></a>5.10. Special lambda expressions</h3></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794563"></a>5.10.1. Protect</h4></div></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794571"></a>5.10.2. Const_parameters</h4></div></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794580"></a>5.10.3. Break_const</h4></div></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794588"></a>5.10.4. Unlambda</h4></div></div></div></div></div><div class="section"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2794599"></a>6. Contributors</h2></div></div>
Jaakko Järvi, Gary Powell.
Additional help and ideas: Jeremy Siek, Peter Higley, Peter Dimov