Glossary
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Backus-Naur Form (BNF)
     Formal method of specifying context-free grammars.  BNF was first
     used in the `ALGOL-60' report, 1963.  *Note Languages and
     Context-Free Grammars: Language and Grammar.

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.  *Note Languages and Context-Free
     Grammars: Language and Grammar.

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: Algorithm.

Grouping
     A language construct that is (in general) grammatically divisible;
     for example, `expression' or `declaration' in C.  *Note Languages
     and Context-Free Grammars: Language and Grammar.

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: Language and Grammar.

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: Precedence.

Left recursion
     A rule whose result symbol is also its first component symbol; for
     example, `expseq1 : expseq1 ',' exp;'.  See Recursive Rules: Recursion.

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: Algorithm.

Lexical analyzer (scanner)
     A function that reads an input stream and returns tokens one by
     one.  See The Lexical Analyzer Function `yylex': Lexical.

Lexical tie-in
     A flag, set by actions in the grammar rules, which alters the way
     tokens are parsed.  See Lexical Tie-ins.

Literal string token
     A token which constists of two or more fixed characters.  
See Symbols.

Look-ahead token
     A token already read but not yet shifted.  *Note Look-Ahead
     Tokens: Look-Ahead.

LALR(1)
     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: Mystery Conflicts.

LR(1)
     The class of context-free grammars in which at most one token of
     look-ahead 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.

Parse error
     An error encountered during parsing of an input stream due to
     invalid syntax.  See Error Recovery.

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.  *Note The Bison Parser
     Algorithm: 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: Pure Decl.

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: Recursion.

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: 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: Algorithm.

Single-character literal
     A single character that is recognized and interpreted as is.
     See From Formal Rules to Bison Input: Grammar in Bison.

Start symbol
     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: Start Decl.

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.  *Note Multi-function
     Calc::.

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: Language and Grammar.