xtc.parser
Class VariantSorter

java.lang.Object
  xtc.tree.Visitor
      xtc.parser.VariantSorter

public class VariantSorter
extends Visitor

Visitor to infer a grammar's variants.

This visitor assumes that the entire grammar is contained in a single module. It also assumes that the grammar's real root has been annotated and that directly left-recursive productions have not been transformed into equivalent right-iterations.

Version:

$Revision: 1.34 $

Author:

Robert Grimm

Nested Class Summary

class	VariantSorter.Registrar Visitor to register all generic node names with the type operations class.
class	VariantSorter.Typer Visitor to determine a generic production's variant type.

Field Summary

protected Analyzer	analyzer The analyzer.
protected AST	ast The type operations.
protected java.util.List<Element>	elements The list of elements representing the current alternative.
protected VariantSorter.Typer	gtyper The generic production typer.
protected boolean	hasChanged The flag for whether productions have changed in push mode.
protected boolean	isGeneric The flag for whether the current production is generic.
protected boolean	isPushMode The flag for whether the current mode is push or pull.
protected java.util.Map<Node,Node>	malformed The set of AST nodes resulting in an error.
protected FullProduction	production The current production.
protected java.util.List<Production>	productions The productions to be processed in push mode.
protected Runtime	runtime The runtime.
protected java.util.List<Type>	types The current types.

Constructor Summary

VariantSorter(Runtime runtime, Analyzer analyzer, AST ast)
Create a new variant sorter.

Method Summary

protected Type	merge(VariantT v1, VariantT v2, Production p) Merge the two variants.
protected void	pushPull(Module m) Push and pull any variant types.
protected void	recurse(Element e) Recurse on the specified element.
protected void	setType(Production p, Type t) Set the specified production's type to the specified type.
void	visit(FullProduction p) Visit the specified production.
void	visit(Module m) Visit the specified grammar.
void	visit(OrderedChoice c) Visit the specified choice.
void	visit(Sequence s) Visit the specified sequence.

Methods inherited from class xtc.tree.Visitor

dispatch, equals, hashCode, iterate, map, mapInPlace, unableToVisit, visit

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Field Detail

runtime

protected final Runtime runtime

The runtime.

analyzer

protected final Analyzer analyzer

The analyzer.

ast

protected final AST ast

The type operations.

gtyper

protected final VariantSorter.Typer gtyper

The generic production typer.

malformed

protected java.util.Map<Node,Node> malformed

The set of AST nodes resulting in an error.

isPushMode

protected boolean isPushMode

The flag for whether the current mode is push or pull.

productions

protected java.util.List<Production> productions

The productions to be processed in push mode.

hasChanged

protected boolean hasChanged

The flag for whether productions have changed in push mode.

types

protected java.util.List<Type> types

The current types. In push mode, the list contains exactly one variant type, which is being pushed through productions. In pull mode, the list contains the types of all alternatives, which may be variant types, type parameters, and error types and which are unified in visit(FullProduction).

production

protected FullProduction production

The current production.

isGeneric

protected boolean isGeneric

The flag for whether the current production is generic. We need to track this information in an explicit flag, because this visitor processes choices and sequences that will be lifted into their own productions.

elements

protected java.util.List<Element> elements

The list of elements representing the current alternative.

Constructor Detail

VariantSorter

public VariantSorter(Runtime runtime,
                     Analyzer analyzer,
                     AST ast)

Create a new variant sorter.

Parameters:

runtime - The runtime.

analyzer - The analyzer utility.

ast - The type operations.

Method Detail

merge

protected Type merge(VariantT v1,
                     VariantT v2,
                     Production p)

Merge the two variants. This method merges the second variant into the first variant, which must be polymorphic. If the second variant also is polymorphic, it simply adds the second variant's tuples to the first variant. Otherwise, it tries to create a new tuple with the second variant's original name and then adds that tuple to the first variant.

Parameters:

v1 - The first variant.

v2 - The second variant.

p - The production for error reporting.

Returns:

The first variant or the error type in case of errors.

setType

protected void setType(Production p,
                       Type t)

Set the specified production's type to the specified type. This method preserves the original type's generic attribute, unless the specified type is the error type.

Parameters:

p - The production.

t - The type.

pushPull

protected void pushPull(Module m)

Push and pull any variant types.

Parameters:

m - The grammar.

visit

public void visit(Module m)

Visit the specified grammar.

visit

public void visit(FullProduction p)

Visit the specified production.

visit

public void visit(OrderedChoice c)

Visit the specified choice.

visit

public void visit(Sequence s)

Visit the specified sequence.

recurse

protected void recurse(Element e)

Recurse on the specified element. If the element is an optionally bound nonterminal, this method processes the corresponding production. If the element is an optionally bound sequence or choice, this method processes the sequence or choice. Otherwise, it reports an error condition and returns.

Parameters:

e - The element.