====== Debugging Support ======

When ACT programs get long, it may be difficult to track down why a particular circuit is not being constructed properly. To help debug this, there are two basic debugging constructs provided.

===== Assertions =====

Sometimes it is useful to be able to check that a parameter (or an expression of parameters) has a reasonable 
value. To express this, ACT supports explicit assertions. We use Hoare's syntax for assertions, so the assertion that 
''x'' must be ''8'' would be written
<code act>
{x=8};
</code>
If a more meaningful message is required, the following syntax is also supported:
<code act>
{x=8 : "This assertion failed"};
</code>
which also reports the message specified when the assertion failed.

During circuit development/debugging, it may be helpful to assert that two signals are connected to each
other or in fact disconnected from each other at a particular point during circuit construction. To assert that ''a'' is connected to ''b'', use:
<code act>
bool a;
bool b;

{ a !== b : "a and b are connected!" };  // this will pass
a = b;
{ a === b : "a and b are not connected!" }; // this will pass
{ a !== b : "a and b are connected!" };  // this will fail
</code>

The operators ''==='' and ''!=='' are used to check that the two signals are connected or disconnected at the point the  assertion was encountered during circuit construction.

===== Log Messages =====

ACT supports debug log messages in verbose mode. A debug log statement can be written as:

<code act>
...
${ "Hello!" };   // log message "Hello"
...
</code>
When this construct is encountered, a log message is displayed. By default these messages are ignored; to see them, use the ''-Vconfig'' ACT command-line option to any ACT tool. (Note that this will also display the names of the configuration files loaded by ACT.)

A log message can include multiple values,  including parameter expressions. This can be useful to check values of parameters.
<code act>
${ "Parameter i has value ", i };  // display the value of i
</code>