| java.lang.Object
 xtc.tree.Visitor
xtc.parser.DirectLeftRecurser
| DirectLeftRecurser | | public class DirectLeftRecurser extends Visitor (Code) | | Visitor to transform direct left-recursions into equivalent
right-recursions. As a practical matter, this visitor transforms
only void, text-only, token-level, and generic productions. For
generic productions, it builds on
xtc.util.Action actions to ensure that the resulting right-recursive productions preserve
the structure of the original productions' semantic values. In
particular, left-associative data structures remain
left-associative, even after transformation. This visitor requires
that all nested choices that do not appear as the last element in a
sequence have been lifted. It also assumes that the entire grammar
is contained in a single module.
This visitor may report errors to the user.
author:
Robert Grimm
version:
$Revision: 1.77 $ |
| Field Summary | |
| final public static int | STATE_BASE
The flag for processing the base case. | | final public static int | STATE_RECURSION
The flag for processing the recursive case. | | final protected Analyzer | analyzer
The analyzer utility. | | final protected AST | ast
The type operations. | | protected List<Binding> | children
The list of variables representing the children of the generic
node to be created. | | protected boolean | hasConstant
The flag for whether the grammar has the
Constants.ATT_CONSTANTconstant attribute. | | protected boolean | hasParseTree
The flag for whether the grammar has the
Constants.ATT_PARSE_TREE parseTree attribute. | | protected boolean | isGeneric
The flag for whether we are transforming a generic production. | | protected boolean | isTextOnly
The flag for whether we are transforming a text-only production. | | protected boolean | isToken
The flag for whether we are transforming a token-level production. | | protected boolean | isTopLevel
Flag for whether the current element is the top-level element of
a production. | | protected boolean | isVoid
The flag for whether we are transforming a void production. | | protected List<NodeMarker> | markers
The list of node markers. | | protected FullProduction | pTail
The new tail production. | | final protected Runtime | runtime
The runtime. | | protected Binding | seed
The binding for the seed value. | | protected boolean | seenChoice
Flag for whether we have processed an ordered choice. | | protected int | state
The current state. | | protected String | varAction
The name of the action's argument. |
| STATE_BASE | | final public static int STATE_BASE(Code) | | The flag for processing the base case.
|
| STATE_RECURSION | | final public static int STATE_RECURSION(Code) | | The flag for processing the recursive case.
|
| ast | | final protected AST ast(Code) | | The type operations.
|
| children | | protected List<Binding> children(Code) | | The list of variables representing the children of the generic
node to be created.
|
| isGeneric | | protected boolean isGeneric(Code) | | The flag for whether we are transforming a generic production.
|
| isTextOnly | | protected boolean isTextOnly(Code) | | The flag for whether we are transforming a text-only production.
|
| isToken | | protected boolean isToken(Code) | | The flag for whether we are transforming a token-level production.
|
| isTopLevel | | protected boolean isTopLevel(Code) | | Flag for whether the current element is the top-level element of
a production.
|
| isVoid | | protected boolean isVoid(Code) | | The flag for whether we are transforming a void production.
|
| seenChoice | | protected boolean seenChoice(Code) | | Flag for whether we have processed an ordered choice.
|
| state | | protected int state(Code) | | The current state.
|
| varAction | | protected String varAction(Code) | | The name of the action's argument.
|
| DirectLeftRecurser | | public DirectLeftRecurser(Runtime runtime, Analyzer analyzer, AST ast)(Code) | | Create a new direct left-recurser.
Parameters:
runtime - The runtime.
Parameters:
analyzer - The analyzer utility.
Parameters:
ast - The type operations. |
| bind | | protected Binding bind(Element e)(Code) | | Create a binding for the specified element. This method also
adds the name of the bound variable to the end of the list of
children.
Parameters:
e - The element to bind. The corresponding binding. |
| isBase | | public static boolean isBase(Sequence s, FullProduction p)(Code) | | Determine whether the specified sequence represents a base case
for a direct left-recursion. The specified sequence must be a
top-level alternative for the specified production, which, in
turn, must be
DirectLeftRecurser.isTransformable transformable .
Parameters:
s - The sequence.
Parameters:
p - The production. true if the specified sequence is a basecase for the direct left-recursion. |
| isRecursive | | public static boolean isRecursive(Sequence s, FullProduction p)(Code) | | Determine whether the specified sequence is directly
left-recursive. The specified sequence must be a top-level
alternative of the specified production, which, in turn, must be
DirectLeftRecurser.isTransformable transformable .
Parameters:
s - The sequence.
Parameters:
p - The production. true if the specified sequence is directlyleft-recursive. |
| isTransformable | | public static boolean isTransformable(FullProduction p)(Code) | | Determine whether the specified production contains a direct
left-recursion that is transformable into the corresponding
right-recursion by this visitor. Note that, for a production to
be transformable, all direct left-recursions must precede the
corresponding base cases. Further nore that this method assumes
that the specified production's element is an ordered choice of
sequences.
Parameters:
p - The production. true if the production is transformableby this visitor. |
| visit | | public void visit(Module m)(Code) | | Process the specified grammar.
|
| visit | | public Element visit(Element e)(Code) | | Visit the specified element. This method provides the default
implementation for repetitions, options, predicates, voided
elements, character terminals, (parser) actions, and value
elements.
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