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echo streamn. astream oftypeecho-stream.

effective methodn. the combination ofapplicable methods that are executed when ageneric function is invoked with a particular sequence ofarguments.

elementn. 1. (of alist) anobject that is thecar of one of theconses that comprise thelist. 2. (of anarray) anobject that is stored in thearray. 3. (of asequence) anobject that is anelement of thelist orarray that is thesequence. 4. (of atype) anobject that is a member of the set ofobjects designated by thetype. 5. (of aninputstream) acharacter ornumber (as appropriate to theelement type of thestream) that is among the ordered series ofobjects that can be read from thestream (usingread-char orread-byte, as appropriate to thestream). 6. (of anoutputstream) acharacter ornumber (as appropriate to theelement type of thestream) that is among the ordered series ofobjects that has been or will be written to thestream (usingwrite-char orwrite-byte, as appropriate to thestream). 7. (of aclass) ageneralized instance of theclass.

element typen. 1. (of anarray) thearray element type of thearray. 2. (of astream) thestream element type of thestream.

emn.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 widestglyph in the font, and other characters' widths are typically fractions of anem. In implementations providing non-Roman characters with wider characters than ``M,'' it is permissible for another character to be theimplementation-defined reference character for this measure, and for ``M'' to be only a fraction of anem wide.) In a fixed width font, a line withn characters isnems wide; in a variable width font,nems is the expected upper bound on the width of such a line.

empty listn. thelist containing noelements. See().

empty typen. thetype that contains noelements, and that is asubtype of alltypes (including itself). Seenil.

end of filen. 1. the point in aninputstream beyond which there is no further data. Whether or not there is such a point on aninteractive stream isimplementation-defined. 2. asituation that occurs upon an attempt to obtain data from aninputstream that is at theend of file[1].

environmentn. 1. a set ofbindings. SeeSection 3.1.1 (Introduction to Environments). 2. anenvironment object. ``macroexpand takes an optional environment argument.''

environment objectn. anobject representing a set oflexical bindings, used in the processing of aform to provide meanings fornames within thatform. ``macroexpand takes an optional environment argument.'' (Theobjectnil when used as anenvironment object denotes thenull lexical environment; thevalues ofenvironment parameters tomacro functions areobjects ofimplementation-dependent nature which represent theenvironment[1] in which the correspondingmacro form is to be expanded.) SeeSection 3.1.1.4 (Environment Objects).

environment parametern. Aparameter in adefining form f for which there is no correspondingargument; instead, thisparameter receives as its value anenvironmentobject which corresponds to thelexical environment in which thedefining form f appeared.

errorn. 1. (only in the phrase ``is an error'') asituation in which the semantics of a program are not specified, and in which the consequences are undefined. 2. acondition which represents anerrorsituation. SeeSection 1.4.2 (Error Terminology). 3. anobject oftypeerror.

error outputn. theoutputstream which is thevalue of thedynamic variable*error-output*.

escapen.,adj. 1.n. asingle escape or amultiple escape. 2.adj.single escape ormultiple escape.

establishv.t. to build or bring into being abinding, adeclaration, anexit point, atag, ahandler, arestart, or anenvironment. ``let establishes lexical bindings.''

evaluatev.t. (aform or animplicit progn) toexecute thecode represented by theform (or the series offorms making up theimplicit progn) by applying the rules ofevaluation, returning zero or more values.

evaluationn. a model wherebyforms areexecuted, returning zero or more values. Such execution might be implemented directly in one step by an interpreter or in two steps by firstcompiling theform and thenexecuting thecompiledcode; this choice is dependent both on context and the nature of theimplementation, but in any case is not in general detectable by any program. The evaluation model is designed in such a way that aconforming implementation might legitimately have only a compiler and no interpreter, or vice versa. SeeSection 3.1.2 (The Evaluation Model).

evaluation environmentn. arun-time environment in which macro expanders and code specified byeval-when to be evaluated are evaluated. All evaluations initiated by thecompiler take place in theevaluation environment.

executev.t.Trad. (code) to perform the imperative actions represented by thecode.

execution timen. the duration of time thatcompiled code is beingexecuted.

exhaustive partitionn. (of atype) a set ofpairwisedisjointtypes that form anexhaustive union.

exhaustive unionn. (of atype) a set ofsubtypes of thetype, whose union contains allelements of thattype.

exit pointn. a point in acontrol form from which (e.g.,block), through which (e.g.,unwind-protect), or to which (e.g.,tagbody) control and possiblyvalues can be transferred both actively by using anothercontrol form and passively through the normal control and data flow ofevaluation. ``catch andblock establish bindings for exit points to whichthrow andreturn-from, respectively, can transfer control and values;tagbody establishes a binding for an exit point with lexical extent to whichgo can transfer control; andunwind-protect establishes an exit point through which control might be transferred by operators such asthrow,return-from, andgo.''

explicit returnn. the act of transferring control (and possiblyvalues) to ablock by usingreturn-from (orreturn).

explicit usen. (of avariable V in aform 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 themacro expansion of theform itself. References to V exposed by expandingsubforms of F are, however, considered to beexplicit uses of V.

exponent markern. a character that is used in the textual notation for afloat to separate the mantissa from the exponent. The characters defined asexponent markers in thestandard readtable are shown in the next figure. For more information, seeSection 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 ddouble-float                             E or efloat (see*read-default-float-format*)  F or fsingle-float                             L or llong-float                               S or sshort-float

Figure 26-1. Exponent Markers

exportv.t. (asymbol in apackage) to add thesymbol to the list ofexternal symbols of thepackage.

exportedadj. (of asymbol in apackage) being anexternal symbol of thepackage.

expressed adjustabilityn. (of anarray) ageneralized boolean that is conceptually (but not necessarily actually) associated with thearray, representing whether thearray isexpressly adjustable. See alsoactual adjustability.

expressed array element typen. (of anarray) thetype which is thearray element type implied by atype declaration for thearray, or which is the requestedarray element type at its time of creation, prior to any selection of anupgraded array element type. (Common Lisp does not provide a way of detecting thistype directly at run time, but animplementation is permitted to make assumptions about thearray's contents and the operations which may be performed on thearray when thistype is noted during code analysis, even if those assumptions would not be valid in general for theupgraded array element type of theexpressed array element type.)

expressed complex part typen. (of acomplex) thetype which is implied as thecomplex part type by atype declaration for thecomplex, or which is the requestedcomplex part type at its time of creation, prior to any selection of anupgraded complex part type. (Common Lisp does not provide a way of detecting thistype directly at run time, but animplementation is permitted to make assumptions about the operations which may be performed on thecomplex when thistype is noted during code analysis, even if those assumptions would not be valid in general for theupgraded complex part type of theexpressed complex part type.)

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

expressly adjustableadj. (of anarray) beingactually adjustable by virtue of an explicit request for this characteristic having been made at the time of its creation. Allarrays that areexpressly adjustable areactually adjustable, but not necessarily vice versa.

extended charactern. acharacter oftypeextended-char: acharacter that is not abase character.

extended function designatorn. adesignator for afunction; that is, anobject that denotes afunction and that is one of: afunction name (denoting thefunction it names in theglobal environment), or afunction (denoting itself). The consequences are undefined if afunction name is used as anextended function designator but it does not have a global definition as afunction, or if it is asymbol that has a global definition as amacro or aspecial form. See alsofunction designator.

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

extensionn. a facility in animplementation of Common Lisp that is not specified by this standard.

extentn. the interval of time during which areference to anobject, abinding, anexit point, atag, ahandler, arestart, or anenvironment is defined.

external file formatn. anobject ofimplementation-dependent nature which determines one of possibly severalimplementation-dependent ways in whichcharacters are encoded externally in acharacterfile.

external file format designatorn. adesignator for anexternal file format; that is, anobject that denotes anexternal file format and that is one of: thesymbol:default (denoting animplementation-dependent defaultexternal file format that can accomodate at least thebase characters), some otherobject defined by theimplementation to be anexternal file format designator (denoting animplementation-definedexternal file format), or some otherobject defined by theimplementation to be anexternal file format (denoting itself).

external symboln. (of apackage) asymbol that is part of the `external interface' to thepackage and that areinherited[3] by any otherpackage thatuses thepackage. When using theLisp reader, if apackage prefix is used, thename of anexternal symbol is separated from thepackagename by a singlepackage marker while thename of aninternal symbol is separated from thepackagename by a doublepackage marker; seeSection 2.3.4 (Symbols as Tokens).

externalizable objectn. anobject that can be used as aliteralobject incode to be processed by thefile compiler.

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