Labels and Gotos

It is sometimes useful to be able to jump directly to some code location. Labels provide a way to mark a location in the code and the builtin $goto can jump to a label :

$print("enter");
$goto(next);
$print("skipping");
next:
$print("done");

Please note that label identifiers are global to the file, but cannot be defined in all expressions. The reason is to simplify the compiler since labels normally require multiple passes for stack preservation (see below). In the case a label cannot be declared, an error is printed at compilation-time. The builtin $goto can only be used with a valid label identifier, in that case only, the identifier is treated as a label and not as a variable.

Gotos and Stack Preservation

In all cases, gotos going to labels are preserving the stack. For example, in the following case, the variable "x" is popped out of the stack when the goto occurs :

{
	var x = 0;
	$goto(next);
}
next:

If the goto is done inside a block having defined local variables, these variables are also accessible, but their values are unspecified :

$goto(next);
{
	var x = 0;
	next:
	$print(x);
}

Gotos and Exceptions

In the same way gotos are preserving the stack size, they are also preserving the exception handlers, such that the following program is correctly compiled :

try {
	$goto(next);
} catch e {
	...
}
next:

In the case a goto is done inside a try...catch block, a temporary exception handler will be set that will only reraise the exception. The exception is not handled by the catch block since the try setup have been skipped :

$goto(next);
try {
	next:
	$throw("error");
} catch e {
	...
}
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