org.nineml.coffeegrinder.trees

Interface Axe

All Known Implementing Classes:

PriorityAxe, RandomAxe, SequentialAxe

public interface Axe

An axe is a tool an Arborist might use to extract trees from a forest.

Method Summary

Modifier and Type	Method and Description
void	forArborist(Arborist arborist) Who's using this axe?
boolean	isSpecialist() Is this a specialist axe?
java.util.List<Family>	select(ParseTree tree, ForestNode forestNode, int count, java.util.List<Family> choices) Select a branch from a list of branches.
boolean	wasAmbiguousSelection() Was the previous selection ambiguous?

Method Detail

isSpecialist

boolean isSpecialist()

Is this a specialist axe?

A specialist axe can consider every tree in the forest differently every time it is used. A non-specialist axe considers every tree at most once and returns all the trees that are selected.

Returns:

true if the axe is specialist

select

java.util.List<Family> select(ParseTree tree,
                              ForestNode forestNode,
                              int count,
                              java.util.List<Family> choices)

Select a branch from a list of branches.

In an ambiguous forest, some nodes will have more than one possible choice. In any given tree, only one choice may be selected. This function is called to make the selection.

There will always be at least one element in the choices list when the method is called. The method must return at least one.

The first node in the list returned is the choice selected for the tree currently under construction. If only one choice is returned, the node becomes unambiguous on subsequent parses, the same selection will always be used. If additional choices are returned, they will be considered on subsequent parses. Note that if you want the selected choice to be considered on future parses, it must appear in the list twice. It is the only node that may appear twice.

Parameters:

tree - the parent node in the parse tree

forestNode - the forest node

count - the number of times node has occurred in this parse

choices - the possible paths

Returns:

the acceptable paths

Throws:

java.lang.NullPointerException - if null is returned

TreeWalkerException - if an invalid choice is made

wasAmbiguousSelection

boolean wasAmbiguousSelection()

Was the previous selection ambiguous?

This method asks if the previous selection was ambiguous. If the axe ever indicates that an ambiguous selection was made, the resulting parse is considered ambiguous. For example, the SequentialAxe always returns true because it treats all choices as equivalent. The PriorityAxe only considers a selection ambiguous if there wasn't a uniquely highest priority selection.

Returns:

true if the choice made was random

forArborist

void forArborist(Arborist arborist)

Who's using this axe?

Do not pass the same axe to more than one Arborist.

Parameters:

arborist - the Arborist using this axe.