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package bjc.pratt;
import bjc.pratt.commands.DefaultInitialCommand;
import bjc.pratt.commands.DefaultNonInitialCommand;
import bjc.utils.data.ITree;
import bjc.utils.funcutils.NumberUtils;
import bjc.utils.parserutils.ParserException;
import java.util.HashMap;
import java.util.Map;
/**
* A configurable Pratt parser for expressions.
*
* @author EVE
*
* @param <K>
* The key type for the tokens.
*
* @param <V>
* The value type for the tokens.
*
* @param <C>
* The state type of the parser.
*
*
*/
public class PrattParser<K, V, C> {
/*
* Default commands that error when used.
*/
private final NonInitialCommand<K, V, C> DEFAULT_LEFT_COMMAND = new DefaultNonInitialCommand<>();
private final InitialCommand<K, V, C> DEFAULT_NULL_COMMAND = new DefaultInitialCommand<>();
/*
* Left-commands that depend on what the null command was.
*/
private Map<K, Map<K, NonInitialCommand<K, V, C>>> dependantLeftCommands;
/*
* The left commands.
*/
private Map<K, NonInitialCommand<K, V, C>> leftCommands;
/*
* The initial commands.
*/
private Map<K, InitialCommand<K, V, C>> nullCommands;
/*
* Initial commands only checked for statements.
*/
private Map<K, InitialCommand<K, V, C>> statementCommands;
/**
* Create a new Pratt parser.
*
*/
public PrattParser() {
dependantLeftCommands = new HashMap<>();
leftCommands = new HashMap<>();
nullCommands = new HashMap<>();
statementCommands = new HashMap<>();
}
/**
* Parse an expression.
*
* @param precedence
* The initial precedence for the expression.
*
* @param tokens
* The tokens for the expression.
*
* @param state
* The state of the parser.
*
* @param isStatement
* Whether or not to parse statements.
*
* @return The expression as an AST.
*
* @throws ParserException
* If something goes wrong during parsing.
*/
public ITree<Token<K, V>> parseExpression(int precedence, TokenStream<K, V> tokens, C state,
boolean isStatement) throws ParserException {
if (precedence < 0) {
throw new IllegalArgumentException("Precedence must be greater than zero");
}
Token<K, V> initToken = tokens.current();
tokens.next();
K initKey = initToken.getKey();
ITree<Token<K, V>> ast;
if (isStatement && statementCommands.containsKey(initKey)) {
ast = statementCommands.getOrDefault(initKey, DEFAULT_NULL_COMMAND).denote(initToken,
new ParserContext<>(tokens, this, state));
} else {
ast = nullCommands.getOrDefault(initKey, DEFAULT_NULL_COMMAND).denote(initToken,
new ParserContext<>(tokens, this, state));
}
int rightPrec = Integer.MAX_VALUE;
while (true) {
Token<K, V> tok = tokens.current();
K key = tok.getKey();
NonInitialCommand<K, V, C> command = leftCommands.getOrDefault(key, DEFAULT_LEFT_COMMAND);
if (dependantLeftCommands.containsKey(initKey)) {
command = dependantLeftCommands.get(initKey).getOrDefault(key, command);
}
int leftBind = command.leftBinding();
if (NumberUtils.between(precedence, rightPrec, leftBind)) {
tokens.next();
ast = command.denote(ast, tok, new ParserContext<>(tokens, this, state));
rightPrec = command.nextBinding();
} else {
break;
}
}
return ast;
}
/**
* Add a non-initial command to this parser.
*
* @param marker
* The key that marks the command.
*
* @param comm
* The command.
*/
public void addNonInitialCommand(K marker, NonInitialCommand<K, V, C> comm) {
leftCommands.put(marker, comm);
}
/**
* Add a initial command to this parser.
*
* @param marker
* The key that marks the command.
*
* @param comm
* The command.
*/
public void addInitialCommand(K marker, InitialCommand<K, V, C> comm) {
nullCommands.put(marker, comm);
}
/**
* Add a statement command to this parser.
*
* The difference between statements and initial commands is that
* statements can only appear at the start of the expression.
*
* @param marker
* The key that marks the command.
*
* @param comm
* The command.
*/
public void addStatementCommand(K marker, InitialCommand<K, V, C> comm) {
statementCommands.put(marker, comm);
}
/**
* Add a dependant non-initial command to this parser.
*/
public void addDependantCommand(K dependant, K marker, NonInitialCommand<K, V, C> comm) {
if (dependantLeftCommands.containsKey(dependant)) {
dependantLeftCommands.get(dependant).put(marker, comm);
} else {
Map<K, NonInitialCommand<K, V, C>> comms = new HashMap<>();
comms.put(marker, comm);
dependantLeftCommands.put(dependant, comms);
}
}
}
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