Java Reference
In-Depth Information
G
rammar
(S): Creates a new grammar with start symbol S. The grammar
does not yet contain any productions.
P
roduction
,
rhs
): Creates a new production for nonterminal A and returns
a descriptor for the production. The iterator
rhs
supplies the symbols for
the production's RHS.
(A
P
roductions
( ): Returns an iterator that visits each of the grammar's produc-
tions in no particular order.
N
onterminal
(A): Adds A to the set of nonterminals. An error occurs if A
is already a terminal symbol. The function returns a descriptor for the
nonterminal.
T
erminal
( x ): Adds x to the set of terminals. An error occurs if x is already a
nonterminal symbol. The function returns a descriptor for the terminal.
N
on
T
erminals
( ): Returns an iterator for the set of nonterminals.
T
erminals
( ): Returns an iterator for the set of terminal symbols.
I
s
T
erminal
(
X
): Returns
true
if
X
is a terminal; otherwise, returns
false
.
RHS(
p
): Returns an iterator for the symbols on the RHS of production
p
.
LHS(
p
): Returns the nonterminal defined by production
p
.
P
roductions
F
or
(A): Returns an iterator that visits each production for non-
terminal A.
O
ccurrences
(
X
): Returns an iterator that visits each occurrence of
X
in the
RHS of all rules.
P
roduction
(
y
): Returns a descriptor for the production A
→α
where
α
con-
tains the occurrence
y
of some vocabulary symbol.
T
ail
(
y
): Accesses the symbols appearing after an occurrence. Given a symbol
occurrence
y
in the rule A
→α
y
β
,T
ail
(
y
) returns an iterator for the
symbols in
β
.
One of the most common grammar computations determines which nonter-
minals can derive
. This information is important because such nonterminals
may disappear during a parse and hencemust be handled carefully. Determin-
ing if a nonterminal can derive
λ
λ
is not entirely trivial because the derivation
can take more than one step:
A
⇒
BCD
⇒
BC
⇒
B
⇒λ.
