fri.patterns.interpreter.parsergenerator.lexer
Class Strategy

java.lang.Object
  |
  +--fri.patterns.interpreter.parsergenerator.lexer.Strategy

All Implemented Interfaces:

java.io.Serializable

public class Strategy

extends java.lang.Object

implements java.io.Serializable

Strategy is the way how alternative concurrent character consumers are applied to input. It is used by LexerImpl and ConsumerAlternatives. There are consumers that have a fixed start character and others that have not. Consumers have different length of fixed start sequences. Some consumers have a fixed length to scan, others (with repeatable rules) have not. Consumers differ in their character sets, some having many possible characters, others lesser, some sets might overlap those of other consumers. Last but not least the Parser gives hints about currently expected tokens.

Following is the strategy implemented here:

• Divide consumers in two groups: those with fixed start character and those without.
• Sort both consumers groups by
  1. by the variance of their start character (which may be a set), the less the better
  2. their start sequence length (ends before first repeatable character), the longer the better
  3. by their fixed start length (ends before first character set), the longer the better This is done by Consumer implements Comparable.
• The lookahead character chooses consumers with fixed start character.
• If one matches, overlapping consumers without fixed start character are tried, when one scans longer, it wins.
• If none matches, consumers without fixed start character are tried, by sort order.
• If one matches, overlapping consumers without fixed start character are tried, when one scans longer, it wins.

Author:

Fritz Ritzberger

See Also:

Serialized Form

Nested Class Summary

static class

Strategy.Item The List item wrapper for toplevel consumers.

Constructor Summary

Strategy()

Method Summary

void	addIgnoringConsumer(java.lang.String symbol, fri.patterns.interpreter.parsergenerator.lexer.Consumer cc) Adds a Consumer to list of possible consumers.
void	addTokenConsumer(java.lang.String symbol, fri.patterns.interpreter.parsergenerator.lexer.Consumer cc) Adds a Consumer to list of possible consumers producing valid tokens.
Strategy.Item	consume(fri.patterns.interpreter.parsergenerator.lexer.InputText input, int lookahead, java.util.Map expectedTokenSymbols) Liefert null wenn kein consumer den input lesen kann, sonst den laengstmoeglichen gescannten Text.
boolean	hasTerminal(java.lang.String terminal) Returns true if the passed terminal is already in list.
void	setCompeteForLongestInput(boolean competeForLongestInput)
java.lang.String	toString() Returns a human readable representation of the lists and maps within this strategy.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Strategy

public Strategy()

Method Detail

setCompeteForLongestInput

public void setCompeteForLongestInput(boolean competeForLongestInput)

addIgnoringConsumer

public void addIgnoringConsumer(java.lang.String symbol,
                                fri.patterns.interpreter.parsergenerator.lexer.Consumer cc)

Adds a Consumer to list of possible consumers. This consumer will read input to be ignored by the parser.

addTokenConsumer

public void addTokenConsumer(java.lang.String symbol,
                             fri.patterns.interpreter.parsergenerator.lexer.Consumer cc)

Adds a Consumer to list of possible consumers producing valid tokens.

hasTerminal

public boolean hasTerminal(java.lang.String terminal)

Returns true if the passed terminal is already in list.

consume

public Strategy.Item consume(fri.patterns.interpreter.parsergenerator.lexer.InputText input,
                             int lookahead,
                             java.util.Map expectedTokenSymbols)
                      throws java.io.IOException

Liefert null wenn kein consumer den input lesen kann, sonst den laengstmoeglichen gescannten Text.

Parameters:

input - the input to read from

lookahead - the first byte or character from input

expectedTokenSymbols - expected token symbols (in key enumeration), can be null

java.io.IOException

toString

public java.lang.String toString()

Returns a human readable representation of the lists and maps within this strategy.

Overrides:

toString in class java.lang.Object