function-information

Arguments: fspec &optional env all-declarations special-operators

This function returns information about the operator named by fspec when it is found in the functional position in the environment env. env may be an environment object or nil, indicating the null lexical environment. all-declarations is a boolean which requests a building of all declarations out of previous declarations of the same name, including the global environment. This switch is added so that the interpreter, which almost never looks at declarations, doesn't need to cons as much for no good reason. special-operaor is a boolean which controls whether :special-operator is returned for the first value when fspec names both a macro and a special-operator in certain cases (see below for more information). The default is nil, and :macro is returned in that case.

Four values are returned.

The first value returned is one of the following values, providing information about the type of definition or binding of fspec:

• nil: there is no binding or definition of fspec.
• :function: fspec refers to a function.
• :macro: fspec refers to a macro.
• :compiler-macro: fspec has a compiler macro associated with it. (If the symbol names both a macro and a compiler macro, see below for details.)
• :special-operator: fspec refers to a special operator. (If fspec refers to both a macro and a special operator, see below for details.)

The second returned value is a locative cons (a cons whose car and/or cdr may be used as a mutable value). This locative cons is used to provide the local binding of the value (for :evaluation environments) or local compiler structure information (for the compiler/compilation environments). To reduce consing at critical points in the environments implementation, there are a few exceptions where the second value is not a cons representing a locative:

• When the first return value from function-information is :special-operator, then the second value is nil, because the value of a special operator is opaque to the programmer (companion-macros are mandated by the spec in order for a non-compiler to "see" into special-operators, and so a functional value does not make sense).
• When the first return value from function-information is either :function or :macro, and the definition is in fact dynamic and thus accessible via fdefinition or macro-function, respectively, then the second returned value is nil, unless the third argument to function-information is non-nil, indicating that consing definitions and declarations is ok.

The third returned value is an alist containing information declarations that apply to the bindings of symbol. The keys are symbols that name declaration specifiers (such as dynamic-extent, inline, ftype, etc.) and the value is the associated value.

The fourth returned value is a boolean indicating whether definition is local or global: the value is true if the binding is local, nil if not. (In CLtL-2, this local/global boolean is the second returned value.)

If one considers a namespace to be a one-to-one mapping of a name to a binding, then the function namespace is not a pure namespace in Common Lisp; consider that a name can simultaneously name both a special-operator and either a macro or a compiler-macro, or it can name a macro or function and a compiler-macro simultaneously. Of course, any lexical definition created for that name (such as an flet, labels, or macrolet) will shadow all of these potential combinations, but if no such shadowing occurs, there is a necessity for function-information to be able to make the distinctions between the various combinations of definition that are possible.

If the fourth argument (the special-operators argument) to function-information is true, and if the name is a non-shadowed special-operator, then :special-operator is returned, even if it has a macro or a compiler-macro definition as well. If the argument is nil, then for a special-operator which also has a compiler-macro, :compiler-macro is returned only for :compiler or :compilation environments (otherwise :special-operator is returned), and for a special-operator which also has a macro definition, :macro is returned only for :interpreter and :evaluation environments (otherwise :special-operator is returned).

We do not define what occurs if a special-operator has both a macro and a compiler-macro definition, beause Allegro CL has none of these situations. There should be a normalized behavior for such situation.

If a name defines a compiler-macro as well as either a macro or a function, then which is returned depends on the environment kind: a :compiler or :compilation environment will cause the :compiler-macro to be returned, and an :interpreter or an :evaluation environment will result in the :function or :macro being returned.

See environments.htm for more information on environments.

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This page was not revised from the 10.0 page.
Created 2019.8.20.