AttrOf

Used to fetch an attribute of a node with the given name.

attrOf val name<id>

Returns the attribute named name from val.

If name is type, the lookup refers to the type attribute of the node. Otherwise, the lookup is performed on the node’s non-type attributes.

If an attribute is not found through the procedure above and val is a type, a lookup is performed on its type-specific attributes.

import "std/io.orb";

data Foo {
    x:i32
}::((xTy i32));

fnc main () () {
    eval (sym (x 0::mark));

    attrOf x mark;  # true
    attrOf Foo xTy; # i32
};

There are two types of attributes: the type attribute (defined using :) and non-type attributes (defined using ::).

Each non-type attribute has a name and a value. The name must not be the identifier type. Node attributes may not share names. If the value is not specified, it is implicitly true.

Attribute values must be evaluated, and of a non-owning type.

Node attributes are preserved in invocation arguments, raw elements, and evaluated ref values.

After a node is processed, if the original node had a type attribute, it overrides the type attribute of the resulting node. The same applies to non-type attributes (as a whole, not per individual attribute).