Final Vocab Flashcards
(226 cards)
1
Q
absolute code
A
computer program code that is executable without
further processing: all addresses in the code are absolute.
cf. relocatable code.
2
Q
abstract syntax tree (AST)
A
a tree representation of a program
that is abstracted from the details of a particular programming
language and its surface syntax.
3
Q
accepting state
A
a state of a finite automaton in which the input string is accepted
as being a member of the language recognized by the automaton.
4
Q
actual parameter
A
a parameter used in a call to a subprogram. cf. formal parameter.
5
Q
address alignment
A
see storage alignment.
6
Q
adjacency matrix
A
a method of representing a graph by a Boolean
matrix M , where M_{ij = 1 iff there is an arc from node i
to node j in the graph.
7
Q
aliasing
A
the creation of an alternate name for data, either in the definition of
a program or during its operation.
8
Q
alphabet
A
a set of symbols used in the definition of a language.
9
Q
ambiguity
A
a case where more than one interpretation is possible.
10
Q
ambiguous grammar
A
a grammar that allows some sentence or string to be generated
or parsed in more than one way (i.e., with distinct parse trees).
11
Q
antisymmetric
A
a relation * is antisymmetric iff
forall a, b . a b and b a –> a = b .
Example <=
12
Q
arity
A
the number of arguments of a function.
13
Q
associativity
A
a specification of the order in which operations should be performed
when two operators of the same precedence are adjacent. Most operators
are left-associative, e.g. the expression A - B - C
should be interpreted as ((A - B) - C).
14
Q
augmented transition network (ATN)
A
a formalism for describing parsers, especially for natural language.
Similar to a finite automaton, but augmented in that arbitrary tests may be
attached to transition arcs, subgrammars may be called recursively, and
structure-building actions may be executed as an arc is traversed.
15
Q
automatic programming
A
synthesis of a program that satisfies a
specification, where the specification is higher-level than ordinary
programming languages.
16
Q
available
A
an expression is available if it has been computed previously in the
computation path preceding the current location and has not been killed.
17
Q
AVL tree
A
self-balancing binary search tree
18
Q
backpatching
A
filling in the address of a label, which has just become defined, in preceding parts of the program that made forward references to it.
19
Q
backward referencing
A
a reference to an earlier statement in the program
20
Q
base address
A
the address of the beginning of a data area. This address is added to a relative address or offset to compute an absolute address.
21
Q
basic block
A
a sequence of program statements such that if any of them is executed, all
of them are; a sequence of statements that has a label (if any) only at the
beginning and a branch (if any) only at the end.
22
Q
basic type
A
a data type that is implemented in computer hardware
instructions, such as integer or real.
23
Q
bit vector
A
a sequence of Boolean values (0 or 1) represented as the
bits of one or more computer words. It is an efficient representation
for sets that are subsets of a fairly small finite set of possible elements.
24
Q
BNF
A
Backus-Naur Form, a syntax for writing context-free grammars
that describe computer languages.
25
Boolean matrix
a matrix whose elements are Boolean values, 0
or 1.
26
bottom-up parsing
a parsing method in which input words are matched against the right-hand
sides of grammar productions in an attempt to build a parse tree from the
bottom towards the top.
27
boxed number
a form of number storage that contains type information as well as a numeric value, e.g. Integer in Java.
28
BSS
a pseudo-operation for some assemblers, used to specify the
reservation of a block of storage, perhaps initialized to some constant
value. (an abbreviation of Block Starting with Symbol.)
29
busy
describes a variable whose value will be needed later during
program execution. Also, live.
30
cache prefetch
an instruction that causes the contents
of a specified memory address to be fetched from main memory into the cache
memory so that it will be available for fast access when needed.
31
call by name
a form of parameter transmission in which the effect of a textual
substitution of the actual parameter for the formal parameter is achieved
32
call by reference
a form of parameter transmission in which the address of the actual
parameter is transmitted to the subprogram. Any changes to the parameter
made by the subprogram will change the argument as seen by the calling
program.
33
call by value
a form of parameter transmission in which the value of the actual
parameter is transmitted to the subprogram. Changes to the parameter
made by the subprogram will not be seen by the calling program.
34
callee-saved
registers whose value must be preserved by a subprogram. The subprogram can either not use those registers, or save their values and restore them before exiting. Also, nonvolatile.
35
caller-saved
registers whose value may be destroyed by a subprogram. If the calling program wants to save those values, it must do so. Also, volatile.
36
canonical form
a standardized form of expressions or data. If all programs put their
expressions into a canonical form, the number of cases that will have
to be considered by other programs is reduced.
37
Cartesian product
if A and B are sets, the Cartesian product
A X B is the set of ordered pairs (a, b) where
a in A and b in B .
38
cascading errors
a situation, e.g. in compiling a program, where one error causes many
reported errors. For example, failure to declare a variable may cause
an error every time that variable is referenced.
39
cast
to coerce a given value to be of a specified type.
40
Chomsky hierarchy
the hierarchy of formal language types: regular, context free, context
sensitive, and recursively enumerable languages, each of which is a proper
subset of the following class.
41
CKY parser
a kind of parser, due to Cocke, Kasami, and Younger, that efficiently produces all possible parses of an input. Also written CYK.
42
class
in object-oriented programming, a description of a set of similar objects.
For example, Fido, an object or instance, might be a member of the class Dogs.
43
code generation
the phase of a compiler in which executable output code is generated
from intermediate code.
44
code motion
the movement of code by a compiler to a place other than where it appears
in the source program. For example, an expensive but unchanging
computation might be moved outside a loop.
45
collision
in a hash table, a case in which a symbol has the same
hash function value as another symbol.
46
column-major order
a method of storing arrays in which values in a column of the array
are in adjacent memory locations. cf. row-major order.
47
computed
of a subexpression, having its value computed within a given block of code.
48
concatenation
making a sequence that consists of the elements of a first sequence
followed by those of a second sequence.
49
condition code register
A CPU register that describes the result of the last arithmetic operation
or comparison. It typically contains bits for <0, =0,
>0, carry, and overflow.
50
constant folding
performing at compile time an operation whose
operands are constant, giving a new constant result.
51
context-free grammar
a grammar in which the left-hand side of each production consists of a
single nonterminal symbol.
52
control flow analysis
analysis of the possible paths that control flow
may take in a program during execution.
53
dangling reference
in execution of a program, a reference, usually by means of a pointer,
to storage that has been deallocated. For example, in a recursive
language, a pointer to storage that is allocated on the execution stack
could be retained after the routine associated with that stack frame has
exited, resulting in errors.
54
data area
a contiguous area of memory, specified by its base address and size.
Data within the area are referenced by the base address of the area and
the offset, or relative address, of the data within the area.
55
data flow analysis
analysis of places in the programs where data
receive values and the places where those data values can subsequently be used.
56
dead code
parts of a program that cannot be reached during execution and therefore
can never be executed.
57
declaration
a statement in a programming language that provides
information to the compiler, such as the structure of a data record,
but does not specify executable code.
58
defined
of a variable, having received a value prior to a given point in a program.
59
definition-use chain
the portion of a program flow graph across which a
variable is both defined and live (busy), beginning at the point where
the variable receives a value and ending at the last place that value is used.
Also, du-chain.
60
derivation
a list of steps that shows how a sentence
in a language is derived from a grammar by application of grammar rules.
61
deterministic finite automaton
a finite automaton that has at most one transition from a state for each
input symbol and no empty transitions. Abbreviated DFA.
62
disambiguating rules
rules that allow an ambiguous situation to be resolved to a single
outcome, e.g. rules of operator precedence.
63
dominator
a basic block of a program is a dominator of a second block if every
path from the entry of the program to the second block passes through it.
64
dynamic
refers to things that happen or can only be determined
during actual execution of a program. cf. static.
65
dynamic memory
memory that is assigned during execution of a program, especially heap
memory.
66
dynamic type checking
testing of the types of the values of variables at runtime, as is done
in Lisp and object-oriented languages. cf. static type checking.
67
enumerated type
a scalar type consisting of a finite set of
enumerated values, e.g. type boolean = (false, true);.
68
epilogue
a section of code that is executed just before leaving a subprogram
to restore register values, transfer the result of the subprogram to
the calling program, and branch to the return address.
69
equivalent grammars
grammars that denote the same language.
70
error production
a grammar production, as in a Yacc grammar,
that is executed if no other production matches the input.
71
finite automaton
an abstract computer consisting of an alphabet of symbols, a finite
set of states, a starting state, a subset of accepting states, and
transition rules that specify transitions from one state to another
depending on the input symbol. The machine begins in the starting
state; for each input symbol, it makes a transition as specifies by the
transition rules. If the automaton is in an accepting state at the end
of the input, the input is recognized. Also, finite state machine.
Abbreviated FA.
72
formal parameter
a parameter specified in the argument list of a procedure definition.
cf. actual parameter.
73
forward reference
reference to a label in a program that has not yet appeared in the program
text.
74
fragmentation
the breaking up of memory into blocks that are too small to be of use.
cf. internal fragmentation, external fragmentation.
75
garbage
storage that can no longer be accessed because no pointer to it exists.
76
garbage collection
the identification of unused storage and collection of it so that it can
be placed back on the heap for reuse.
77
global optimization
optimization based on analysis of the entire
program or procedure.
78
grammar
a formal specification of a language, consisting of a set of nonterminal
symbols, a set of terminal symbols or words, and production rules that specify
transformations of strings containing nonterminals into other strings.
79
graph
a (directed) graph is a pair ( S, Gamma ) where S is a set of
nodes and Gamma subset S X S is a set of transitions between
nodes.
80
graph coloring
an algorithm for assigning a minimal number of ``colors'' to nodes of
a graph such that no two nodes that are connected have the same color.
Used in compilers as a method of register assignment: colors correspond
to registers, nodes to variables or def-use chains, and connections to
variables that are simultaneously live.
81
hash function
a deterministic function that converts converts a
symbol or other input to a ``randomized'' integer value.
82
hash table
a table that associates key values with data by use of
a hash function.
83
hash with buckets
a form of hash table in which the hash code denotes a bucket or set of entries whose keys hash to that value
84
heap
an area of contiguous memory and/or a set of unused storage records that
can be allocated to the running program as dynamic memory upon request;
the address of the record is returned and assigned to a pointer variable.
new in Pascal, malloc in C, and cons in Lisp allocate
heap memory.
85
infix
an expression written with an operator between its operand,
e.g. a + b . cf. prefix, postfix.
86
implicit parameter
a parameter that is passed to a subprogram without being specified directly
by the programmer, e.g., the return address.
87
induction variable
a variable that is incremented during a loop and used to perform a similar
action on multiple data; also, loop index.
88
inherit
to use a method defined in a superclass.
89
inherited attribute
an attribute of a node in a parse tree that is derived from the context
in which the node appears. cf. synthesized attribute.
90
inlining
inserting code of a subprogram directly into the code compiled for the
calling program, rather than compiling a subroutine call to an external
procedure.
91
insertion
placement of a new data item in its proper position in an ordered sequence, such as a list, array, or symbol table
92
instance
in object-oriented programming, an individual data object
that is an instance of a class of similar objects. Also, object.
93
instance variable
a data field in an instance.
94
intermediate language
an internal language used as the representation of a program during
compilation, such as trees or quadruples. The source language is
translated to intermediate language, then to the object language.
95
interpreted code
a form of program that is read and executed by an interpreter program.
The interpreter reads an instruction, determines its meaning, and executes it.
96
interval
a set of basic blocks of a program that comprise a sequence of statements or
simple loop.
97
keyword
a special word that is used to indicate the structure of a language,
such as the reserved words of computer languages.
98
killed
of a subexpression, having any previously computed value invalidated
by redefinition of a component of the subexpression. Note that the term
``killed'' cannot properly be applied to a program variable.
99
Kleene closure
zero or more occurrences of a grammar item;
indicated by a superscript *
100
language denoted by a grammar
L(G), the set of strings that can
be derived from a grammar, beginning with the start symbol.
101
left-associative
an operator in an arithmetic expression such that if there are two adjacent
occurrences of the operator, the left one should be done first.
102
left factoring
a method of modifying a grammar to eliminate left recursion.
103
left recursion
in top-down parsing, a grammar rule whose right-hand side begins with the
nonterminal symbol on the left-hand side will cause an infinite recursion,
called left recursion. Also, describes such a production.
104
leftmost derivation
a derivation in which the leftmost nonterminal of the string is replaced
at each step.
105
lexeme
a basic symbol in a language; e.g., a variable name would be a lexeme for
a grammar of a programming language.
106
lexer
lexical analyzer. (a program that performs lexical analysis, reading characters and producing the internal form of lexemes.)
107
lexical analysis
parsing and conversion to internal form of the simplest elements of a
language, usually specified by a regular grammar, such as variable
names, numbers, etc.
108
lexical scoping
a convention in a block-structured programming language that a variable
can only be referenced within the block in which it is defined and
blocks contained within that block; thus, the scope of a variable is
completely determined at compile time. cf. dynamic scoping.
109
link editor
a program that combines relocatable code modules to form an executable
absolute code file. The link editor assigns memory locations for each
relocatable module, relocates relative addresses to form absolute
addresses, finds library modules whose names are referenced as external
symbols and includes those modules in the loading process, and fills in
absolute addresses for external references between modules.
110
live variable
a variable whose value will be used at a later point during execution.
111
loader
a program in the operating system that executes an absolute program by
allocating storage for it in main memory, reading the program into memory,
and jumping to its entry point. Sometimes link-editing is performed prior
to loading.
112
local optimization
optimization that can be done correctly taking
into account only a small part of the program.
113
location counter
1. a counter that denotes the next location in memory for code or
data during assembly or compilation of a program.
2. a numeric value that denotes the location of the beginning of a data
area, which is added to addresses during relocation.
114
loop unrolling
conversion of a loop into straight-line code by repetition of the code inside the loop with successive values of the loop index substituted into the code. for ( i = 0; i < 3; i++) x[i] = y[i]; could be unrolled to { x[0] = y[0]; x[1] = y[1]; x[2] = y[2]; }
115
macro
a statement in a programming language that is expanded into
one or more statements in the same language, by substitution of
arguments into a language pattern or by construction of the statements
by a program.
116
mark-and-sweep
a method of garbage collection in which all storage that is in use is
marked, then all storage that is not marked is swept up for reuse.
117
materialization
to store in memory as a discrete data value; to make a copy in memory of
otherwise transient data, such as a value in a register.
118
memory hierarchy
a hierarchy of different kinds of computer memory, in which there is a
small amount of costly fast memory (such as registers or cache) and
increasing amounts of slower kinds of memory.
119
memory leak
failure to return dynamic memory that is no longer in use; eventually
causes the program to run out of memory.
120
message
in object-oriented programming, an indirect function call.
A message is sent to an object; the selector of the message
(an abstract procedure name) is looked up in the class to which the
object belongs to determine the method that is the actual function
that is called.
121
method
in an object-oriented system, a procedure associated with a class that performs
the action associated with a message.
122
multiple inheritance
in an object-oriented system, the ability of a
class to have multiple superclasses and to inherit methods from all of them.
123
name equivalence
type equivalence testing in which two types are considered equal only if
they have the same name. cf. structural equivalence.
124
NaN
Not a Number, a floating-point value that does not represent a valid number. This could result from use of uninitialized data (if memory is initialized to NaN's), arithmetic performed on a NaN, or an undefined operation such as 0/0. A NaN may be quiet, or signalling, in which case its generation or use generates a CPU exception.
125
nondeterministic finite automaton
a finite automaton that has multiple state transitions from a single state
for a given input symbol, or that has a null transition, not requiring an
input symbol. Abbreviated NFA.
126
nonterminal
a symbol that names a phrase in a grammar.
127
nonvolatile register
a register whose value must be preserved across a procedure call.
128
object
in an object-oriented programming system, a data structure containing
instance variables and a pointer to the class to which the object belongs.
129
object language
the output language of a compiler.
130
object-oriented programming
a style of programming based on the use of
objects and messages, as opposed to data structures and procedure
calls.
131
observability
the ability to observe the state of a system. For software, the provision of built-in code to allow the internal operations of a program to be easily observed.
132
offset
the location of data relative to the start of a data area.
133
operand
a data value upon which an operation is performed.
134
operator
a symbol that denotes an operation to be performed on data in an expression.
135
optimization
transformation of a program to produce a program whose input-output
behavior is equivalent to that of the original program, but that has lower cost,
e.g. faster execution time.
136
overloading
the assignment of multiple meanings to an operator, depending on the type
of data to which it is applied; e.g., the symbol + could represent
integer addition, floating-point addition, or matrix addition.
137
padding
insertion of an area of unused storage in order to achieve storage alignment.
138
Pareto distribution
informally, a distribution in which most of a phenomenon is accounted for by a fraction of a population: 90% of execution time is spent in 10% of code.
139
parametric polymorphism
polymorphism in which type expressions
are parameterized, e.g. list of T where T is a type parameter.
140
parse tree
a data structure that shows how a statement in a language is derived from
the context-free grammar of the language; it may be annotated with additional
information, e.g. for compilation purposes.
141
parsing
the process of reading a source language, determining its structure,
and producing intermediate code for it.
142
partial evaluation
optimization of a program by evaluating parts of the program that are
constant at compile time. This may include unrolling loops and algebraic
optimization of operations involving constant data; the resulting program
may be larger, but faster and more suitable for parallel execution.
143
partition
a division of a set into disjoint subsets whose union
is the set. A partition corresponds to an equivalence relation
144
pass
a phase of a compiler or assembler in which the entire source program
(in its original form or some later representation) is processed.
145
peephole optimization
a kind of optimization, performed on generated code by a compiler,
in which a linear pass is made over the code examining a small region
of code to see if it can be improved; e.g., a jump instruction to the
next sequential location can be eliminated.
146
polymorphic function
a function that can operate on data of more than one type.
147
postamble
see epilogue.
148
postfix
a way of writing expressions in which an operator appears
after its operands: ab+.
149
postincrement
a CPU feature in which the value of an index register is automatically
incremented by a fixed amount after its use, thus pointing to the next data
in an array.
150
preamble
see prologue.
151
precedence
an ordering of operators that specifies that certain operators should
be performed before others when no ordering is otherwise specified.
152
prefix
1. a contiguous set of symbols at the beginning of a
string. 2. a way of writing expressions in which an operator appears
before its operands: +ab.
153
preorder
an order of visiting trees, in which a node is examined first, followed
by recursive examination of its children, in left-to-right order, in
the same fashion
154
production
a rule of a context-free grammar, specifying that a nonterminal symbol
can be replaced by another string of symbols.
155
prologue
a section of code that is executed immediately upon entry to a subprogram
to save register values, save the return address, and transfer parameters
to the subprogram.
156
quadruples
a form of intermediate program code used in compilers, equivalent to
a small ``assignment statement'' of the form ``R = X op Y'' where R
is the result, X and Y are operands, and op is the operation.
157
recognizer
a program or abstract device that can read a string of symbols and decide
whether the string is a member of a particular language.
158
record
a data area consisting of contiguous component fields,
which may be of different types.
159
recursive descent
a method of writing a parser in which a grammar rule is written as a
procedure that recognizes that phrase, calling subroutines as needed for
sub-phrases and producing a parse tree or other data structure as output.
160
reduce-reduce conflict
in a grammar for a shift-reduce parser,
a case in which an input might be reduced by more than one production.
161
reduction in strength
an optimization in which an operator is changed to a less-expensive
operator; e.g., x * 2 becomes x + x
162
reduction step
in shift-reduce parsing, the reduction of items at the top of the stack
to a phrase that encompasses those items.
163
referenced
of a variable, having its value read within a sequence of
code.
164
reflexive transitive closure
in a graph, the mapping from each node to the set of nodes that can be
reached from it in 0 or more steps.
165
register windows
a technique used in the SPARC architecture in which the CPU has a stack of registers and a stack frame or window of these registers is used by a given procedure.
166
regular expression
an algebraic expression that denotes a regular language.
167
regular grammar
a grammar that denotes a regular language; its productions can only have
on the right-hand side either a terminal string or a terminal string
followed by a single nonterminal.
168
regular language
a language described by a regular grammar, or recognizable by a finite
automaton, e.g. a simple item such as a variable name or a number in a
programming language.
169
rehash
1. in a hash table storage scheme, to calculate a new hash value for an item when the previous hash value caused a collision with an existing item. 2. the algorithm used to calculate the new hash value.
170
relation
a subset of the Cartesian product of two sets.
171
relocatable code
program code that can be relocated to run in different locations in
computer memory. Addresses within the program are specified relative to
location counters; external addresses are specified by symbolic names.
172
relocation
the process performed by a link editor to convert relocatable code
into absolute code that can be executed, by adding the absolute starting
address of a data area to relative addresses of data within that data area.
173
reserved word
a word in a programming language that is reserved for
use as part of the language and may not be used as an identifier.
174
restore registers
to load nonvolatile registers with the saved values that the registers
had upon entry to a subprogram.
175
return address
the address immediately following a call to a subprogram; the subprogram
returns when finished by branching to this address.
176
reverse Polish
an unambiguous, parenthesis-free notation for expressing an arithmetic
expression. Operators appear after their operands.
177
right-associative
an operator in an arithmetic expression such that if there are two adjacent
occurrences of the operator, the right one should be done first.
178
RISC
reduced instruction set computer. A CPU in which only a basic set
of instructions is provided and in which extra responsibilities may be
placed upon the compiler, e.g. not using the result of an instruction
until after a certain amount of time has passed.
179
row-major order
a method of storing a multi-dimensional array, such that elements of a row
of the array are adjacent in memory. cf. column-major order.
180
save registers
to save the values of nonvolatile registers upon entry to a subprogram
so that the values can be restored before the subprogram exits.
181
scalar type
a data type that occupies a fixed amount of storage.
182
selector
in object-oriented programming, an abstract procedure name or
name of a message action. The class describes the association between the
selector and the corresponding method that performs that action for objects
in the class.
183
semantics
the meaning of a statement in a language. cf. syntax.
184
send a message
the action of sending a message to (calling a method on) an object.
185
shadowing
a case where a name that is closer to the point of use prevents finding the same name in a different context that is farther away. For example, a method name such as .hashCode() that is defined for a Java class will shadow and override the .hashCode() that is defined for Object
186
shift-reduce conflict
in a grammar for a shift-reduce parser,
a case in which an input might either be shifted onto the stack or reduced.
187
shift-reduce parser
a parser that operates by alternately shifting input elements onto the
top of a stack or reducing a group of elements from the top of the stack to
a larger element representing a phrase.
188
significand
the fractional part of a floating-point number; also, mantissa
189
sound type system
a type system of a programming language in which it is guaranteed that
the value of a variable at runtime can only be of the type that was
determined for that variable at compile time; i.e., there can be no
runtime type errors.
190
spill code
code to store the values of some registers into main memory so that the
registers can be used for other purposes.
191
stack frame
a collection of the local variables of a procedure, as well as return
address, saved register values, etc. that are put on the execution
stack for each invocation of a procedure. Also, activation record
192
stack pointer
a CPU register that points to the start of the current stack frame and
is used as an index register to access data within the stack frame.
193
start symbol, S
he initial, or ``sentence'' nonterminal symbol S of a grammar.
194
static
refers to things that can be determined or performed
prior to execution of a program, e.g., at compile time.
cf. dynamic.
195
static analysis
analysis of a program by examining it, but without running it.
196
static type checking
checking or determination of the types of variables in a language at
compile time. This eliminates the need for dynamic type checking, but
requires that a variable have only a single type.
197
storage allocation
the assignment of memory locations to data
and program code.
198
string
a sequence of symbols or characters.
199
strong typing
a system of static type checking in which the types of all variables must
be declared and correct use of types is enforced by the compiler.
200
structural equivalence
a form of type checking in which two types are considered to be equivalent
if they have the same basic data type, or if they have the same
kind of structure whose components are structurally equivalent.
cf. name equivalence.
201
subrange
a contiguous subsequence of a sequence, e.g. 1..10
is a subrange of integer.
202
substring
a sequence of symbols that matches a contiguous subsequence of another string.
203
suffix
a sequence of symbols at the end of a string.
204
superclass
in object-oriented programming, a superset of other
classes. A superclass can provide methods that are inherited by its
subclasses. Mammal might be a superclass of Dog.
205
superscalar
a type of CPU design in which, although there is only a single instruction
stream, certain operations that are nearby in that stream can be
executed concurrently using independent functional units in the CPU.
206
symbol table
a data structure that associates a name (symbol) with
information about the named object.
207
syntax
the rules by which legitimate statements can be constructed.
cf. semantics.
208
syntax directed translation
in parsing a programming language, building the translation of a statement
or construct in a mechanical way from the translations of its syntactic
components.
209
synthesized attribute
an attribute of a structure, e.g. a phrase in a programming language
statement, that is derived from the attributes of its components. For
example, the sum of two floating-point quantities will also be
floating-point.
210
synthesized translation
a method of translating statements, e.g. in a programming language,
such that the translation of a phrase is built up from the translations
of its components.
211
tag
a small-integer field that is attached to data to describe its type
212
terminal
a symbol in a phrase structure grammar that is a part of the language
described by the grammar, such as a word or character of the language.
cf. nonterminal symbol.
213
token
a word, name, or sequence of characters having a meaning as a unit
in a language.
214
top-down parsing
a predictive form of parsing, such as recursive descent, in which the
parse tree of a statement is constructed starting at the root (sentence
symbol).
215
transitive closure
a relation formed from another relation by making it transitive.
Beginning with the original relation, if a b and b c ,
then a * c is added.
In a graph, the mapping from each node to the set of nodes that can be
reached from it in one or more steps.
216
triples
a form of intermediate code used in a compiler, consisting of an operator and two operands. Also called two-address code.
217
type
a description of a kind of variables, including a set of
possible values and a set of operations.
218
type coercion
the automatic conversion of data from its existing type into the type
required for an operation.
219
type constructor
an operator that makes a type from other types,
e.g. array or record.
220
type hierarchy
. in an object-oriented system, the hierarchy of data types formed
by the class-superclass relationships.
2. in general, a lattice of data types formed by containment
by higher types, e.g., integers are a subset of reals, which are
a subset of complex numbers.
221
type lattice
a lattice structure that shows which types are higher or derivable from others, e.g. float is higher than integer. When an operation is specified on different types, the arguments may be coerced to the least upper bound of the two types in the lattice.
222
type signature
type signature
a specification of the argument types and result type of a function or
procedure, e.g. push: item X stack --> stack
223
union type
a type formed by the union of other types, i.e. a member of the
union type can have the type of any one of its component types.
224
unreachable code
program code that cannot be executed because it is
impossible to get to it.
225
variable
an element of computer memory that can hold a value.
226
volatile register
a register whose value may be destroyed during a subroutine call.
