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6.1.3.2 Definitions

Definitions are implemented as an object-oriented hierarchy rooted in the definition class. The complete description of this hierarchy is provided in the Declt (reference)Reference Manual. This section provides an overview of the hierarchy in question, along with the most important remarks about it. Every definition class in the hierarchy has a name of the form foo-definition. For concision, and except for the definition and mixin classes, all class names in the figures below are abbreviated: a foo-definition class is simply denoted as foo. Abstract classes are drawn in red boxes with bold text, regular classes in blue boxes with normal font, and mixins (also abstract) in green ellipses with bold text.

As depicted in Figure 6.1, there are three main categories of definitions: component-definition is the root class for ASDF components, package-definition is the class for Lisp packages, and symbol-definition is the root class of all programmatic definitions named by symbols. The definition root class provides common properties, such as a reference to the corresponding Lisp object (when applicable), source information, and foreign status.

Figure 6.2 depicts the hierarchy of ASDF definitions. Unsurprisingly, this hierarchy closely follows that of actual ASDF components, although some peculiarities are worth mentioning here.

• The lisp-file-definition class corresponds to the ASDF cl-source-file one. Note that ASDF provides two additional subclasses for Lisp files, with extensions ‘.cl’ and ‘.lsp’. We don’t do that, however. Instead, there is a protocol for retrieving a file component’s extension.
• Notice the existence of a system-file-definition class, which is a subclass of lisp-file-definition. In ASDF, system files are not represented as components, but Declt pretends they are by faking a particular class of Lisp files for them. This allows us to document .asd files as particular Lisp files, without too much specific code. Note also that some (few) libraries list their system files (for example as static files) in the system definition. Declt is aware of this and removes such definitions, so as to avoid duplication.

The hierarchy of definitions named by symbols (under the symbol-definition class) is quite large, so it is split into four figures.

The varoid ones (Figure 6.3) represent simple values having symbolic names. This boils down to variables, symbol macros, and slots.

The funcoid ones (Figure 6.4) covers “parametric values”, that is, values having a lambda-list of some sort. This includes all variations on functions, macros, methods, types, setf expanders, and method combinations. You may wonder why the combination-definition class is not abstract. That is because the standard method combination is an instance of it. All funcoids have a slot indicating whether the definition is a setf one (e.g. a function named (setf foo)). The “setfable” branch represents definitions that may be related to a setf expander (that is, which could be either an access-fn or an update-fn). As a matter of fact, this hierarchy is not 100% correct: some funcoids can never be setf ones, and some setfable ones can never be related to a setf expander. On the other hand, doing it like this keeps said hierarchy relatively simple.

The “accessor” sub-branches represent definitions for methods, ordinary, or generic functions, which have been identified as reading or writing slots. The accessor mixin provides a back reference to the slot definition in question. Note that generic functions do not access slots; only their methods do (which is why the generic accessor branch does not use the accessor mixin). A generic function will be qualified as a generic reader (respectively a generic writer) if all its methods have been identified as reader (respectively writer) methods.

The classoid branch (Figure 6.5) represents (typed) structures, classes, and conditions. This part of the definitions hierarchy is probably not portable, as it relies on how SBCL implements a number of things, in particular, which classoids are in fact CLOS classes, which is represented by the CLOS classoid mixin. The CLOS classoid mixin provides super- and sub-classoid information, but this may change in the future. Indeed, it is perhaps possible to trace back :include information for typed structures as well, but this is not currently implemented.

Finally, the last group of symbol definitions is for aliases, that is, globally defined (compiler) macros or functions that are also manually attached to other symbols. Aliases are known to Declt so as to avoid duplicating documentation.