I/O customization variable n. one of the stream variables in the next figure, or some other (implementation-defined) stream variable that is defined by the implementation to be an I/O customization variable.

*debug-io*        *error-io*         query-io*       
*standard-input*  *standard-output*  *trace-output*  

Figure 26-2. Standardized I/O Customization Variables

identical adj. the same under eq.

identifier n. 1. a symbol used to identify or to distinguish names. 2. a string used the same way.

immutable adj. not subject to change, either because no operator is provided which is capable of effecting such change or because some constraint exists which prohibits the use of an operator that might otherwise be capable of effecting such a change. Except as explicitly indicated otherwise, implementations are not required to detect attempts to modify immutable objects or cells; the consequences of attempting to make such modification are undefined. ``Numbers are immutable.''

implementation n. a system, mechanism, or body of code that implements the semantics of Common Lisp.

implementation limit n. a restriction imposed by an implementation.

implementation-defined adj. implementation-dependent, but required by this specification to be defined by each conforming implementation and to be documented by the corresponding implementor.

implementation-dependent adj. describing a behavior or aspect of Common Lisp which has been deliberately left unspecified, that might be defined in some conforming implementations but not in others, and whose details may differ between implementations. A conforming implementation is encouraged (but not required) to document its treatment of each item in this specification which is marked implementation-dependent, although in some cases such documentation might simply identify the item as ``undefined.''

implementation-independent adj. used to identify or emphasize a behavior or aspect of Common Lisp which does not vary between conforming implementations.

implicit block n. a block introduced by a macro form rather than by an explicit block form.

implicit compilation n. compilation performed during evaluation.

implicit progn n. an ordered set of adjacent forms appearing in another form, and defined by their context in that form to be executed as if within a progn.

implicit tagbody n. an ordered set of adjacent forms and/or tags appearing in another form, and defined by their context in that form to be executed as if within a tagbody.

import v.t. (a symbol into a package) to make the symbol be present in the package.

improper list n. a list which is not a proper list: a circular list or a dotted list.

inaccessible adj. not accessible.

indefinite extent n. an extent whose duration is unlimited. ``Most Common Lisp objects have indefinite extent.''

indefinite scope n. scope that is unlimited.

indicator n. a property indicator.

indirect instance n. (of a class C1) an object of class C2, where C2 is a subclass of C1. ``An integer is an indirect instance of the class number.''

inherit v.t. 1. to receive or acquire a quality, trait, or characteristic; to gain access to a feature defined elsewhere. 2. (a class) to acquire the structure and behavior defined by a superclass. 3. (a package) to make symbols exported by another package accessible by using use-package.

initial pprint dispatch table n. the value of *print-pprint-dispatch* at the time the Lisp image is started.

initial readtable n. the value of *readtable* at the time the Lisp image is started.

initialization argument list n. a property list of initialization argument names and values used in the protocol for initializing and reinitializing instances of classes. See Section 7.1 (Object Creation and Initialization).

initialization form n. a form used to supply the initial value for a slot or variable. ``The initialization form for a slot in a defclass form is introduced by the keyword :initform.''

input adj. (of a stream) supporting input operations (i.e., being a ``data source''). An input stream might also be an output stream, in which case it is sometimes called a bidirectional stream. See the function input-stream-p.

instance n. 1. a direct instance. 2. a generalized instance. 3. an indirect instance.

integer n. an object of type integer, which represents a mathematical integer.

interactive stream n. a stream on which it makes sense to perform interactive querying. See Section 21.1.1.1.3 (Interactive Streams).

intern v.t. 1. (a string in a package) to look up the string in the package, returning either a symbol with that name which was already accessible in the package or a newly created internal symbol of the package with that name. 2. Idiom. generally, to observe a protocol whereby objects which are equivalent or have equivalent names under some predicate defined by the protocol are mapped to a single canonical object.

internal symbol n. (of a package) a symbol which is accessible in the package, but which is not an external symbol of the package.

internal time n. time, represented as an integer number of internal time units. Absolute internal time is measured as an offset from an arbitrarily chosen, implementation-dependent base. See Section 25.1.4.3 (Internal Time).

internal time unit n. a unit of time equal to 1/n of a second, for some implementation-defined integer value of n. See the variable internal-time-units-per-second.

interned adj. Trad. 1. (of a symbol) accessible[3] in any package. 2. (of a symbol in a specific package) present in that package.

interpreted function n. a function that is not a compiled function. (It is possible for there to be a conforming implementation which has no interpreted functions, but a conforming program must not assume that all functions are compiled functions.)

interpreted implementation n. an implementation that uses an execution strategy for interpreted functions that does not involve a one-time semantic analysis pre-pass, and instead uses ``lazy'' (and sometimes repetitious) semantic analysis of forms as they are encountered during execution.

interval designator n. (of type T) an ordered pair of objects that describe a subtype of T by delimiting an interval on the real number line. See Section 12.1.6 (Interval Designators).

invalid n., adj. 1. n. a possible constituent trait of a character which if present signifies that the character cannot ever appear in a token except under the control of a single escape character. For details, see Section 2.1.4.1 (Constituent Characters). 2. adj. (of a character) being a character that has syntax type constituent in the current readtable and that has the constituent trait invalid[1]. See Figure 2-8.

iteration form n. a compound form whose operator is named in the next figure, or a compound form that has an implementation-defined operator and that is defined by the implementation to be an iteration form.

do              do-external-symbols  dotimes  
do*             do-symbols           loop     
do-all-symbols  dolist                        

Figure 26-3. Standardized Iteration Forms

iteration variable n. a variable V, the binding for which was created by an explicit use of V in an iteration form.

• DOTIMES-IGNORE:X3J13-MAR91
• PLIST-DUPLICATES:ALLOW
• WITH-STANDARD-IO-SYNTAX-READTABLE:X3J13-MAR-91