CLHS: Glossary-Section E

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E

echo stream n. a stream of type echo-stream.

effective method n. the combination of applicable methods that are executed when a generic function is invoked with a particular sequence of arguments.

element n. 1. (of a list) an object that is the car of one of the conses that comprise the list. 2. (of an array) an object that is stored in the array. 3. (of a sequence) an object that is an element of the list or array that is the sequence. 4. (of a type) an object that is a member of the set of objects designated by the type. 5. (of an input stream) a character or number (as appropriate to the element type of the stream) that is among the ordered series of objects that can be read from the stream (using read-char or read-byte, as appropriate to the stream). 6. (of an output stream) a character or number (as appropriate to the element type of the stream) that is among the ordered series of objects that has been or will be written to the stream (using write-char or write-byte, as appropriate to the stream). 7. (of a class) a generalized instance of the class.

element type n. 1. (of an array) the array element type of the array. 2. (of a stream) the stream element type of the stream.

em n. Trad. a context-dependent unit of measure commonly used in typesetting, equal to the displayed width of of a letter ``M'' in the current font. (The letter ``M'' is traditionally chosen because it is typically represented by the widest glyph in the font, and other characters' widths are typically fractions of an em. In implementations providing non-Roman characters with wider characters than ``M,'' it is permissible for another character to be the implementation-defined reference character for this measure, and for ``M'' to be only a fraction of an em wide.) In a fixed width font, a line with n characters is n ems wide; in a variable width font, n ems is the expected upper bound on the width of such a line.

empty list n. the list containing no elements. See ().

empty type n. the type that contains no elements, and that is a subtype of all types (including itself). See nil.

end of file n. 1. the point in an input stream beyond which there is no further data. Whether or not there is such a point on an interactive stream is implementation-defined. 2. a situation that occurs upon an attempt to obtain data from an input stream that is at the end of file[1].

environment n. 1. a set of bindings. See Section 3.1.1 (Introduction to Environments). 2. an environment object. ``macroexpand takes an optional environment argument.''

environment object n. an object representing a set of lexical bindings, used in the processing of a form to provide meanings for names within that form. ``macroexpand takes an optional environment argument.'' (The object nil when used as an environment object denotes the null lexical environment; the values of environment parameters to macro functions are objects of implementation-dependent nature which represent the environment[1] in which the corresponding macro form is to be expanded.) See Section 3.1.1.4 (Environment Objects).

environment parameter n. A parameter in a defining form f for which there is no corresponding argument; instead, this parameter receives as its value an environment object which corresponds to the lexical environment in which the defining form f appeared.

error n. 1. (only in the phrase ``is an error'') a situation in which the semantics of a program are not specified, and in which the consequences are undefined. 2. a condition which represents an error situation. See Section 1.4.2 (Error Terminology). 3. an object of type error.

error output n. the output stream which is the value of the dynamic variable *error-output*.

escape n., adj. 1. n. a single escape or a multiple escape. 2. adj. single escape or multiple escape.

establish v.t. to build or bring into being a binding, a declaration, an exit point, a tag, a handler, a restart, or an environment. ``let establishes lexical bindings.''

evaluate v.t. (a form or an implicit progn) to execute the code represented by the form (or the series of forms making up the implicit progn) by applying the rules of evaluation, returning zero or more values.

evaluation n. a model whereby forms are executed, returning zero or more values. Such execution might be implemented directly in one step by an interpreter or in two steps by first compiling the form and then executing the compiled code; this choice is dependent both on context and the nature of the implementation, but in any case is not in general detectable by any program. The evaluation model is designed in such a way that a conforming implementation might legitimately have only a compiler and no interpreter, or vice versa. See Section 3.1.2 (The Evaluation Model).

evaluation environment n. a run-time environment in which macro expanders and code specified by eval-when to be evaluated are evaluated. All evaluations initiated by the compiler take place in the evaluation environment.

execute v.t. Trad. (code) to perform the imperative actions represented by the code.

execution time n. the duration of time that compiled code is being executed.

exhaustive partition n. (of a type) a set of pairwise disjoint types that form an exhaustive union.

exhaustive union n. (of a type) a set of subtypes of the type, whose union contains all elements of that type.

exit point n. a point in a control form from which (e.g., block), through which (e.g., unwind-protect), or to which (e.g., tagbody) control and possibly values can be transferred both actively by using another control form and passively through the normal control and data flow of evaluation. ``catch and block establish bindings for exit points to which throw and return-from, respectively, can transfer control and values; tagbody establishes a binding for an exit point with lexical extent to which go can transfer control; and unwind-protect establishes an exit point through which control might be transferred by operators such as throw, return-from, and go.''

explicit return n. the act of transferring control (and possibly values) to a block by using return-from (or return).

explicit use n. (of a variable V in a form F) a reference to V that is directly apparent in the normal semantics of F; i.e., that does not expose any undocumented details of the macro expansion of the form itself. References to V exposed by expanding subforms of F are, however, considered to be explicit uses of V.

exponent marker n. a character that is used in the textual notation for a float to separate the mantissa from the exponent. The characters defined as exponent markers in the standard readtable are shown in the next figure. For more information, see Section 2.1 (Character Syntax). ``The exponent marker `d' in `3.0d7' indicates that this number is to be represented as a double float.''

    Marker  Meaning
    D or d  double-float
    E or e  float (see *read-default-float-format*)
    F or f  single-float
    L or l  long-float
    S or s  short-float

Figure 26-1. Exponent Markers

export v.t. (a symbol in a package) to add the symbol to the list of external symbols of the package.

exported adj. (of a symbol in a package) being an external symbol of the package.

expressed adjustability n. (of an array) a generalized boolean that is conceptually (but not necessarily actually) associated with the array, representing whether the array is expressly adjustable. See also actual adjustability.

expressed array element type n. (of an array) the type which is the array element type implied by a type declaration for the array, or which is the requested array element type at its time of creation, prior to any selection of an upgraded array element type. (Common Lisp does not provide a way of detecting this type directly at run time, but an implementation is permitted to make assumptions about the array's contents and the operations which may be performed on the array when this type is noted during code analysis, even if those assumptions would not be valid in general for the upgraded array element type of the expressed array element type.)

expressed complex part type n. (of a complex) the type which is implied as the complex part type by a type declaration for the complex, or which is the requested complex part type at its time of creation, prior to any selection of an upgraded complex part type. (Common Lisp does not provide a way of detecting this type directly at run time, but an implementation is permitted to make assumptions about the operations which may be performed on the complex when this type is noted during code analysis, even if those assumptions would not be valid in general for the upgraded complex part type of the expressed complex part type.)

expression n. 1. an object, often used to emphasize the use of the object to encode or represent information in a specialized format, such as program text. ``The second expression in a let form is a list of bindings.'' 2. the textual notation used to notate an object in a source file. ``The expression `'sample` is equivalent to `(quote sample)`.''

expressly adjustable adj. (of an array) being actually adjustable by virtue of an explicit request for this characteristic having been made at the time of its creation. All arrays that are expressly adjustable are actually adjustable, but not necessarily vice versa.

extended character n. a character of type extended-char: a character that is not a base character.

extended function designator n. a designator for a function; that is, an object that denotes a function and that is one of: a function name (denoting the function it names in the global environment), or a function (denoting itself). The consequences are undefined if a function name is used as an extended function designator but it does not have a global definition as a function, or if it is a symbol that has a global definition as a macro or a special form. See also function designator.

extended lambda list n. a list resembling an ordinary lambda list in form and purpose, but offering additional syntax or functionality not available in an ordinary lambda list. ``defmacro uses extended lambda lists.''

extension n. a facility in an implementation of Common Lisp that is not specified by this standard.

extent n. the interval of time during which a reference to an object, a binding, an exit point, a tag, a handler, a restart, or an environment is defined.

external file format n. an object of implementation-dependent nature which determines one of possibly several implementation-dependent ways in which characters are encoded externally in a character file.

external file format designator n. a designator for an external file format; that is, an object that denotes an external file format and that is one of: the symbol `:default` (denoting an implementation-dependent default external file format that can accomodate at least the base characters), some other object defined by the implementation to be an external file format designator (denoting an implementation-defined external file format), or some other object defined by the implementation to be an external file format (denoting itself).

external symbol n. (of a package) a symbol that is part of the `external interface' to the package and that are inherited[3] by any other package that uses the package. When using the Lisp reader, if a package prefix is used, the name of an external symbol is separated from the package name by a single package marker while the name of an internal symbol is separated from the package name by a double package marker; see Section 2.3.4 (Symbols as Tokens).

externalizable object n. an object that can be used as a literal object in code to be processed by the file compiler.

The following X3J13 cleanup issue, not part of the specification, applies to this section:

- CHARACTER-VS-CHAR:LESS-INCONSISTENT-SHORT

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