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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 java.util.function.Predicate;
import java.util.function.UnaryOperator;
import bjc.utils.data.experimental.IHolder;
import bjc.utils.data.experimental.IPair;
import bjc.utils.data.experimental.Identity;
import bjc.utils.data.experimental.Pair;
import bjc.utils.funcdata.IFunctionalList;
/**
* Creates a parse tree from a postfix expression
*
* @author ben
*
*/
public class TreeConstructor {
private static final class TokenTransformer<T> implements Consumer<T> {
private final class OperatorHandler
implements UnaryOperator<IPair<Deque<AST<T>>, AST<T>>> {
private T element;
public OperatorHandler(T element) {
this.element = element;
}
@Override
public IPair<Deque<AST<T>>, AST<T>> apply(
IPair<Deque<AST<T>>, AST<T>> pair) {
return pair.bind((queuedASTs, currentAST) -> {
return handleOperator(queuedASTs);
});
}
private IPair<Deque<AST<T>>, AST<T>> handleOperator(
Deque<AST<T>> queuedASTs) {
AST<T> newAST;
if (isSpecialOperator.test(element)) {
newAST = handleSpecialOperator.apply(queuedASTs);
} else {
if (queuedASTs.size() < 2) {
throw new IllegalStateException(
"Attempted to parse binary operator without enough operands.\n"
+ "Problem operator is " + element
+ "\nPossible operand is: \n\t"
+ queuedASTs.peek());
}
AST<T> rightAST = queuedASTs.pop();
AST<T> leftAST = queuedASTs.pop();
newAST = new AST<>(element, leftAST, rightAST);
}
queuedASTs.push(newAST);
return new Pair<>(queuedASTs, newAST);
}
}
private IHolder<IPair<Deque<AST<T>>, AST<T>>> initialState;
private Predicate<T> operatorPredicate;
private Predicate<T> isSpecialOperator;
private Function<Deque<AST<T>>, AST<T>> handleSpecialOperator;
public TokenTransformer(
IHolder<IPair<Deque<AST<T>>, AST<T>>> initialState,
Predicate<T> operatorPredicate,
Predicate<T> isSpecialOperator,
Function<Deque<AST<T>>, AST<T>> handleSpecialOperator) {
this.initialState = initialState;
this.operatorPredicate = operatorPredicate;
this.isSpecialOperator = isSpecialOperator;
this.handleSpecialOperator = handleSpecialOperator;
}
@Override
public void accept(T element) {
if (operatorPredicate.test(element)) {
initialState.transform(new OperatorHandler(element));
} else {
AST<T> newAST = new AST<>(element);
initialState.doWith((pair) -> {
pair.doWith((queue, currentAST) -> {
queue.push(newAST);
});
});
initialState.transform((pair) -> {
return pair.bind((queue, currentAST) -> {
return new Pair<>(queue, newAST);
});
});
}
}
}
/**
* Construct a tree from a list of tokens in postfix notation
*
* Only binary operators are accepted.
*
* @param <T>
* The elements of the parse tree
* @param tokens
* The list of tokens to build a tree from
* @param operatorPredicate
* The predicate to use to determine if something is a
* operator
* @return A AST from the expression
*/
public static <T> AST<T> constructTree(IFunctionalList<T> tokens,
Predicate<T> operatorPredicate) {
return constructTree(tokens, operatorPredicate, (op) -> false,
null);
}
/**
* Construct a tree from a list of tokens in postfix notation
*
* Only binary operators are accepted by default. Use the last two
* parameters to handle non-binary operators
*
* @param <T>
* The elements of the parse tree
* @param tokens
* The list of tokens to build a tree from
* @param operatorPredicate
* The predicate to use to determine if something is a
* operator
* @param isSpecialOperator
* The predicate to use to determine if an operator needs
* special handling
* @param handleSpecialOperator
* The function to use to handle special case operators
* @return A AST from the expression
*
* FIXME The handleSpecialOp function seems like an ugly
* interface. Maybe there's a better way to express how that
* works
*/
public static <T> AST<T> constructTree(IFunctionalList<T> tokens,
Predicate<T> operatorPredicate, Predicate<T> isSpecialOperator,
Function<Deque<AST<T>>, AST<T>> handleSpecialOperator) {
if (tokens == null) {
throw new NullPointerException("Tokens must not be null");
} else if (operatorPredicate == null) {
throw new NullPointerException(
"Operator predicate must not be null");
} else if (isSpecialOperator == null) {
throw new NullPointerException(
"Special operator determiner must not be null");
}
IHolder<IPair<Deque<AST<T>>, AST<T>>> initialState = new Identity<>(
new Pair<>(new LinkedList<>(), null));
tokens.forEach(
new TokenTransformer<>(initialState, operatorPredicate,
isSpecialOperator, handleSpecialOperator));
return initialState.unwrap((pair) -> {
return pair.merge((queue, currentAST) -> currentAST);
});
}
}
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