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package bjc.utils.parserutils;
import java.util.Deque;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.function.Consumer;
import java.util.function.Function;
import bjc.utils.funcdata.FunctionalList;
import bjc.utils.funcutils.StringUtils;
/**
* Utility to run the shunting yard algorithm on a bunch of tokens
*
* @author ben
*
* @param <E>
* The type of tokens being shunted
*/
public class ShuntingYard<E> {
private final class TokenShunter implements Consumer<String> {
private FunctionalList<E> output;
private Deque<String> stack;
private Function<String, E> transform;
public TokenShunter(FunctionalList<E> outpt, Deque<String> stack,
Function<String, E> 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, "\\(")) {
stack.push(token);
} else if (StringUtils.containsOnly(token, "\\)")) {
while (stack.peek().equals(token.replace(')', '('))) {
output.add(transform.apply(stack.pop()));
}
stack.pop();
} else {
output.add(transform.apply(token));
}
}
}
/**
* A enum representing the fundamental operator types
*
* @author ben
*
*/
public static enum Operator implements IPrecedent {
/**
* Represents addition
*/
ADD(1),
/**
* Represents division
*/
DIVIDE(4),
/**
* Represents multiplication
*/
MULTIPLY(3),
/**
* Represents subtraction
*/
SUBTRACT(2);
private final int precedence;
private Operator(int prec) {
precedence = prec;
}
/*
* (non-Javadoc)
*
* @see bjc.utils.parserutils.IPrecedent#getPrecedence()
*/
@Override
public int getPrecedence() {
return precedence;
}
}
/**
* Holds all the shuntable operations
*/
private Map<String, IPrecedent> operators;
/**
* Create a new shunting yard with a default set of operators
*/
public ShuntingYard() {
operators = new HashMap<>();
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 token
* The token representing the operator
* @param precedence
* The precedence of the operator
*/
public void addOp(String token, IPrecedent precedence) {
operators.put(token, precedence);
}
private boolean isHigherPrec(String operator, String rightOperator) {
return (operators.containsKey(rightOperator) && operators
.get(rightOperator).getPrecedence() >= operators
.get(operator).getPrecedence());
}
/**
* 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 FunctionalList<E> postfix(FunctionalList<String> input,
Function<String, E> tokenTransformer) {
FunctionalList<E> output = new FunctionalList<>();
Deque<String> stack = new LinkedList<>();
input.forEach(new TokenShunter(output, stack, tokenTransformer));
while (!stack.isEmpty()) {
output.add(tokenTransformer.apply(stack.pop()));
}
return output;
}
/**
* Remove an operator from the list of shuntable operators
*
* @param tok
* The token representing the operator
*/
public void removeOp(String tok) {
operators.remove(tok);
}
}
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