CLHS: Glossary-Section T

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T

t n. 1. a. the boolean representing true. b. the canonical generalized boolean representing true. (Although any object other than nil is considered true as a generalized boolean, `t` is generally used when there is no special reason to prefer one such object over another.) 2. the name of the type to which all objects belong---the supertype of all types (including itself). 3. the name of the superclass of all classes except itself.

tag n. 1. a catch tag. 2. a go tag.

tail n. (of a list) an object that is the same as either some cons which makes up that list or the atom (if any) which terminates the list. ``The empty list is a tail of every proper list.''

target n. 1. (of a constructed stream) a constituent of the constructed stream. ``The target of a synonym stream is the value of its synonym stream symbol.'' 2. (of a displaced array) the array to which the displaced array is displaced. (In the case of a chain of constructed streams or displaced arrays, the unqualified term ``target'' always refers to the immediate target of the first item in the chain, not the immediate target of the last item.)

terminal I/O n. the bidirectional stream that is the value of the variable *terminal-io*.

terminating n. (of a macro character) being such that, if it appears while parsing a token, it terminates that token. See Section 2.2 (Reader Algorithm).

tertiary value n. (of values resulting from the evaluation of a form) the third value, if any, or else nil if there are fewer than three values.

throw v. to transfer control and values to a catch. See the special operator throw.

tilde n. the standard character that is called ``tilde'' (`~`). See Figure 2-5.

time a representation of a point (absolute time) or an interval (relative time) on a time line. See decoded time, internal time, and universal time.

time zone n. a rational multiple of `1/3600` between `-24` (inclusive) and `24` (inclusive) that represents a time zone as a number of hours offset from Greenwich Mean Time. Time zone values increase with motion to the west, so Massachusetts, U.S.A. is in time zone `5`, California, U.S.A. is time zone `8`, and Moscow, Russia is time zone -3. (When ``daylight savings time'' is separately represented as an argument or return value, the time zone that accompanies it does not depend on whether daylight savings time is in effect.)

token n. a textual representation for a number or a symbol. See Section 2.3 (Interpretation of Tokens).

top level form n. a form which is processed specially by compile-file for the purposes of enabling compile time evaluation of that form. Top level forms include those forms which are not subforms of any other form, and certain other cases. See Section 3.2.3.1 (Processing of Top Level Forms).

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

tree n. 1. a binary recursive data structure made up of conses and atoms: the conses are themselves also trees (sometimes called ``subtrees'' or ``branches''), and the atoms are terminal nodes (sometimes called leaves). Typically, the leaves represent data while the branches establish some relationship among that data. 2. in general, any recursive data structure that has some notion of ``branches'' and leaves.

tree structure n. (of a tree[1]) the set of conses that make up the tree. Note that while the car[1b] component of each such cons is part of the tree structure, the objects that are the cars[2] of each cons in the tree are not themselves part of its tree structure unless they are also conses.

true n. any object that is not false and that is used to represent the success of a predicate test. See t[1].

truename n. 1. the canonical filename of a file in the file system. See Section 20.1.3 (Truenames). 2. a pathname representing a truename[1].

two-way stream n. a stream of type two-way-stream, which is a bidirectional composite stream that receives its input from an associated input stream and sends its output to an associated output stream.

type n. 1. a set of objects, usually with common structure, behavior, or purpose. (Note that the expression ``X is of type Sa'' naturally implies that ``X is of type Sb'' if Sa is a subtype of Sb.) 2. (immediately following the name of a type) a subtype of that type. ``The type vector is an array type.''

type declaration n. a declaration that asserts that every reference to a specified binding within the scope of the declaration results in some object of the specified type.

type equivalent adj. (of two types X and Y) having the same elements; that is, X is a subtype of Y and Y is a subtype of X.

type expand n. to fully expand a type specifier, removing any references to derived types. (Common Lisp provides no program interface to cause this to occur, but the semantics of Common Lisp are such that every implementation must be able to do this internally, and some situations involving type specifiers are most easily described in terms of a fully expanded type specifier.)

type specifier n. an expression that denotes a type. ``The symbol `random-state`, the list `(integer 3 5)`, the list `(and list (not null))`, and the class named `standard-class` are type specifiers.''

The following X3J13 cleanup issues, not part of the specification, apply to this section:

- TIME-ZONE-NON-INTEGER:ALLOW
- TAILP-NIL:T

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