Extra features
Attributes and extensions
The language can be extended with attributes, enabling a variety of extensions.
An attribute is of the form #[key.of.extension] or #[key.of.extension = VALUE],
where VALUE can be of the form "STRING", or an expression in catala syntax.
An attribute is always bound to the element directly following it: an extension
could for example make use of them to retrieve labels to the input fields of a
scope in order to generate a web form:
declaration scope SomeComputation:
#[form.label = "Enter the number of children satisfying the condition XXX"]
input children_of_age content integer
Built-in attributes
Some attributes affect the Catala compiler itself with built-in support.
Debug print
By adding #[debug.print] in front of an expression in a Catala program, the
value of that expression will be printed upon computation by the interpreter,
when run with the --debug option. It is otherwise ignored by the other
backends.
It is also possible to print the value along with a specific tag using
#[debug.print = "some debug tag"].
Note that, in some cases, due to how the compiler works, debug prints could
appear duplicated or not at all, especially if optimisations are enabled (with
the -O flag). If that happens, try to move the attribute to the root of the
definition.