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package bjc.utils.parserutils;
import java.util.Deque;
import java.util.LinkedList;
import java.util.function.Consumer;
import java.util.function.Function;
import bjc.utils.funcdata.FunctionalList;
import bjc.utils.funcdata.FunctionalMap;
import bjc.utils.funcdata.IList;
import bjc.utils.funcdata.IMap;
import bjc.utils.funcutils.StringUtils;
/**
* Utility to run the shunting yard algorithm on a bunch of tokens
*
* @author ben
*
* @param <TokenType>
* The type of tokens being shunted
*/
public class ShuntingYard<TokenType> {
/**
* A enum representing the fundamental operator types
*
* @author ben
*
*/
public static enum Operator implements IPrecedent {
/**
* Represents addition
*/
ADD(1),
/**
* Represents subtraction
*/
SUBTRACT(2),
/**
* Represents multiplication
*/
MULTIPLY(3),
/**
* Represents division
*/
DIVIDE(4);
private final int precedence;
private Operator(int prec) {
precedence = prec;
}
/*
* (non-Javadoc)
*
* @see bjc.utils.parserutils.IPrecedent#getPrecedence()
*/
@Override
public int getPrecedence() {
return precedence;
}
}
private final class TokenShunter implements Consumer<String> {
private IList<TokenType> output;
private Deque<String> stack;
private Function<String, TokenType> transform;
public TokenShunter(IList<TokenType> outpt, Deque<String> stack,
Function<String, TokenType> transform) {
this.output = outpt;
this.stack = stack;
this.transform = transform;
}
@Override
public void accept(String token) {
if (operators.containsKey(token)) {
while (!stack.isEmpty()
&& isHigherPrec(token, stack.peek())) {
output.add(transform.apply(stack.pop()));
}
stack.push(token);
} else if (StringUtils.containsOnly(token, "\\(")) {
// Handle groups of parenthesis for multiple nesting levels
stack.push(token);
} else if (StringUtils.containsOnly(token, "\\)")) {
// Handle groups of parenthesis for multiple nesting levels
String swappedToken = token.replace(')', '(');
while (!stack.peek().equals(swappedToken)) {
output.add(transform.apply(stack.pop()));
}
stack.pop();
} else {
output.add(transform.apply(token));
}
}
}
/**
* Holds all the shuntable operations
*/
private IMap<String, IPrecedent> operators;
/**
* Create a new shunting yard with a default set of operators
*
* @param configureBasics
* Whether or not basic math operators should be provided
*/
public ShuntingYard(boolean configureBasics) {
operators = new FunctionalMap<>();
if (configureBasics) {
operators.put("+", Operator.ADD);
operators.put("-", Operator.SUBTRACT);
operators.put("*", Operator.MULTIPLY);
operators.put("/", Operator.DIVIDE);
}
}
/**
* Add an operator to the list of shuntable operators
*
* @param operatorToken
* The token representing the operator
* @param precedence
* The precedence of the operator to add
*/
public void addOp(String operatorToken, int precedence) {
this.addOp(operatorToken,
IPrecedent.newSimplePrecedent(precedence));
}
/**
* Add an operator to the list of shuntable operators
*
* @param operatorToken
* The token representing the operator
* @param precedence
* The precedence of the operator
*/
public void addOp(String operatorToken, IPrecedent precedence) {
if (operatorToken == null) {
throw new NullPointerException("Operator must not be null");
}
operators.put(operatorToken, precedence);
}
private boolean isHigherPrec(String leftOperator,
String rightOperator) {
boolean operatorExists = operators.containsKey(rightOperator);
if (!operatorExists) {
return false;
}
int rightPrecedence = operators.get(rightOperator).getPrecedence();
int leftPrecedence = operators.get(leftOperator).getPrecedence();
return rightPrecedence >= leftPrecedence;
}
/**
* Transform a string of tokens from infix notation to postfix
*
* @param input
* The string to transform
* @param tokenTransformer
* The function to use to transform strings to tokens
* @return A list of tokens in postfix notation
*/
public IList<TokenType> postfix(IList<String> input,
Function<String, TokenType> tokenTransformer) {
if (input == null) {
throw new NullPointerException("Input must not be null");
} else if (tokenTransformer == null) {
throw new NullPointerException("Transformer must not be null");
}
IList<TokenType> output = new FunctionalList<>();
Deque<String> stack = new LinkedList<>();
input.forEach(new TokenShunter(output, stack, tokenTransformer));
stack.forEach(
(token) -> output.add(tokenTransformer.apply(token)));
return output;
}
/**
* Remove an operator from the list of shuntable operators
*
* @param token
* The token representing the operator
*/
public void removeOp(String token) {
if (token == null) {
throw new NullPointerException("Token must not be null");
}
operators.remove(token);
}
}
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