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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.Function;
import bjc.utils.data.IPrecedent;
import bjc.utils.funcdata.FunctionalList;
/**
* 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 static enum Operator implements IPrecedent {
ADD(1), DIVIDE(4), MULTIPLY(3), SUBTRACT(2);
private final int precedence;
private Operator(int p) {
precedence = p;
}
/*
* (non-Javadoc)
*
* @see bjc.utils.parserutils.IPrecedent#getPrecedence()
*/
@Override
public int getPrecedence() {
return precedence;
}
}
static {
}
/**
* Holds all the shuntable operations
*/
private Map<String, IPrecedent> ops;
/**
* Create a new shunting yard with a default set of operators
*/
public ShuntingYard() {
ops = new HashMap<>();
ops.put("+", Operator.ADD);
ops.put("-", Operator.SUBTRACT);
ops.put("*", Operator.MULTIPLY);
ops.put("/", Operator.DIVIDE);
}
/**
* Add an operator to the list of shuntable operators
*
* @param tok
* The token representing the operator
* @param prec
* The precedence of the operator
*/
public void addOp(String tok, IPrecedent prec) {
ops.put(tok, prec);
}
private boolean isHigherPrec(String op, String sub) {
return (ops.containsKey(sub) && ops.get(sub).getPrecedence() >= ops
.get(op).getPrecedence());
}
/**
* Transform a string of tokens from infix notation to postfix
*
* @param inp
* The string to transform
* @param transform
* The function to use to transform strings to tokens
* @return A list of tokens in postfix notation
*/
public FunctionalList<E> postfix(FunctionalList<String> inp,
Function<String, E> transform) {
FunctionalList<E> outp = new FunctionalList<>();
Deque<String> stack = new LinkedList<>();
inp.forEach((token) -> {
if (ops.containsKey(token)) {
while (!stack.isEmpty()
&& isHigherPrec(token, stack.peek())) {
outp.add(transform.apply(stack.pop()));
}
stack.push(token);
} else if (token.equals("(")) {
stack.push(token);
} else if (token.equals(")")) {
while (!stack.peek().equals("(")) {
outp.add(transform.apply(stack.pop()));
}
stack.pop();
} else {
outp.add(transform.apply(token));
}
});
while (!stack.isEmpty()) {
outp.add(transform.apply(stack.pop()));
}
return outp;
}
/**
* Remove an operator from the list of shuntable operators
*
* @param tok
* The token representing the operator
*/
public void removeOp(String tok) {
ops.remove(tok);
}
/**
* Add an operator to the list of shuntable operators
*
* @param tok
* The token representing the operator
*/
public void addOp(String tok, int i) {
this.addOp(tok, IPrecedent.newSimplePrecedent(i));
}
}
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