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# 2. ASIS Extensions

ASIS-for-GNAT provides some additional types and queries as ASIS extensions. All these queries are defined and documented in the hierarchy headed by package `Asis.Extensions`. They are referred as "ASIS extensions" or "ASIS extension queries" below.

All the ASIS extensions obey the general ASIS rules:

- When using ASIS extensions, you have to follow the required sequencing of calls

- Only ASIS-defined exceptions propagate outside ASIS extension queries

If the documentation of an ASIS extension query contains a list of "appropriate" `Element` kinds, then the query can be applied only to `Element`s from this list, and it raises `ASIS_Inappropriate_Element` with `Value_Error` status otherwise. If the documentation of an ASIS extension query contains a list of "expected" element kinds, then the query can be applied to an `Element` having any kind, but it returns a meaningful result only for `Element`s from this list.

The current set of ASIS extensions originated from the ASIS implementation needs and from the development of some ASIS tools inside the ASIS-for-GNAT team. The `Asis.Extensions` hierarchy is not necessarily frozen: some further extension queries may be added, and suggestions from ASIS application developers are welcome.

Note that some of the ASIS extensions are implemented as ASIS secondary queries -- that is, the implementation of such a query is a sequence of primary ASIS queries. Some other extensions are pure extensions; that is, their implementation is based on direct access to GNAT's internal data structures.

> 2.1 `Asis.Extensions` |  |
> 2.2 `Asis.Extensions.Flat_Kinds` |  |
> 2.3 `Asis.Extensions.Iterator` |  |

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## 2.1 `Asis.Extensions`

This package, whose spec is located in the file ``asis-extensions.ads'`, contains the declarations of various ASIS extensions, including dynamic `Element` and `Compilation_Unit` list types, placeholder actual parameters for `Asis.Iterator.Traverse_Element`, additional `Element` structural and semantic queries, queries that return information about the status of the source file for a `Compilation_Unit`, queries returning the (images of the) values of static expressions, etc.

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## 2.2 `Asis.Extensions.Flat_Kinds`

The ASIS `Element` classification hierarchy is based on a set of Ada enumeration types, each corresponding to a "level" in the hierarchy. The package `Asis.Extensions.Flat_Kinds`, whose spec is located in the file ``asis-extensions-flat_kinds.ads'`, defines the enumeration type `Flat_Element_Kinds`; this type combines the values of all these types and thus provides a "flat" view onto the syntactic `Element` classification.

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## 2.3 `Asis.Extensions.Iterator`

This package, whose spec is located in the file ``asis-extensions-iterator.ads'`, contains the declarations of `Traverse_Unit` generic procedure that is a generalization of the standard ASIS `Asis.Iterator.Traverse_Element` iterator. `Traverse_Unit` provides the depth-first traversal of the whole syntactical structure of the ASIS Compilation Unit.

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