Backus-Naur Form (BNF; also called “Backus Normal Form”)
Formal method of specifying context-free grammars originally proposed
by John Backus, and slightly improved by Peter Naur in his 1960-01-02
committee document contributing to what became the Algol 60 report.
See Languages and Context-Free Grammars.
Context-free grammars
Grammars specified as rules that can be applied regardless of context.
Thus, if there is a rule which says that an integer can be used as an
expression, integers are allowed anywhere an expression is
permitted. See Languages and Context-Free Grammars.
Dynamic allocation
Allocation of memory that occurs during execution, rather than at
compile time or on entry to a function.
Empty string
Analogous to the empty set in set theory, the empty string is a
character string of length zero.
Finite-state stack machine
A “machine” that has discrete states in which it is said to exist at
each instant in time. As input to the machine is processed, the
machine moves from state to state as specified by the logic of the
machine. In the case of the parser, the input is the language being
parsed, and the states correspond to various stages in the grammar
rules. See The Bison Parser Algorithm.
Generalized LR (GLR)
A parsing algorithm that can handle all context-free grammars, including those
that are not LALR(1). It resolves situations that Bison's
usual LALR(1)
algorithm cannot by effectively splitting off multiple parsers, trying all
possible parsers, and discarding those that fail in the light of additional
right context. See Generalized LR Parsing.
Grouping
A language construct that is (in general) grammatically divisible;
for example, `expression' or `declaration' in C.
See Languages and Context-Free Grammars.
Infix operator
An arithmetic operator that is placed between the operands on which it
performs some operation.
Input stream
A continuous flow of data between devices or programs.
Language construct
One of the typical usage schemas of the language. For example, one of
the constructs of the C language is the if statement.
See Languages and Context-Free Grammars.
Left associativity
Operators having left associativity are analyzed from left to right:
‘a+b+c’ first computes ‘a+b’ and then combines with
‘c’. See Operator Precedence.
Left recursion
A rule whose result symbol is also its first component symbol; for
example, ‘expseq1 : expseq1 ',' exp;’. See Recursive Rules.
Left-to-right parsing
Parsing a sentence of a language by analyzing it token by token from
left to right. See The Bison Parser Algorithm.
The class of context-free grammars that Bison (like most other parser
generators) can handle; a subset of LR(1). See Mysterious Reduce/Reduce Conflicts.
LR(1)
The class of context-free grammars in which at most one token of
lookahead is needed to disambiguate the parsing of any piece of input.
Nonterminal symbol
A grammar symbol standing for a grammatical construct that can
be expressed through rules in terms of smaller constructs; in other
words, a construct that is not a token. See Symbols.
Parser
A function that recognizes valid sentences of a language by analyzing
the syntax structure of a set of tokens passed to it from a lexical
analyzer.
Postfix operator
An arithmetic operator that is placed after the operands upon which it
performs some operation.
Reduction
Replacing a string of nonterminals and/or terminals with a single
nonterminal, according to a grammar rule. See The Bison Parser Algorithm.
Reentrant
A reentrant subprogram is a subprogram which can be in invoked any
number of times in parallel, without interference between the various
invocations. See A Pure (Reentrant) Parser.
Reverse polish notation
A language in which all operators are postfix operators.
Right recursion
A rule whose result symbol is also its last component symbol; for
example, ‘expseq1: exp ',' expseq1;’. See Recursive Rules.
Semantics
In computer languages, the semantics are specified by the actions
taken for each instance of the language, i.e., the meaning of
each statement. See Defining Language Semantics.
Shift
A parser is said to shift when it makes the choice of analyzing
further input from the stream rather than reducing immediately some
already-recognized rule. See The Bison Parser Algorithm.
The nonterminal symbol that stands for a complete valid utterance in
the language being parsed. The start symbol is usually listed as the
first nonterminal symbol in a language specification.
See The Start-Symbol.
Symbol table
A data structure where symbol names and associated data are stored
during parsing to allow for recognition and use of existing
information in repeated uses of a symbol. See Multi-function Calc.
Syntax error
An error encountered during parsing of an input stream due to invalid
syntax. See Error Recovery.
Token
A basic, grammatically indivisible unit of a language. The symbol
that describes a token in the grammar is a terminal symbol.
The input of the Bison parser is a stream of tokens which comes from
the lexical analyzer. See Symbols.
Terminal symbol
A grammar symbol that has no rules in the grammar and therefore is
grammatically indivisible. The piece of text it represents is a token.
See Languages and Context-Free Grammars.