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package bjc.utils.parserutils;
import java.util.Deque;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
import bjc.data.IHolder;
import bjc.data.ITree;
import bjc.data.Pair;
import bjc.data.Tree;
import bjc.utils.parserutils.TreeConstructor.ConstructorState;
import bjc.utils.parserutils.TreeConstructor.QueueFlattener;
/*
* Handle creating ASTs from tokens.
*/
final class TokenTransformer<TokenType> implements Consumer<TokenType> {
/*
* Handle operators
*/
private final class OperatorHandler
implements UnaryOperator<ConstructorState<TokenType>> {
/* The handled element. */
private final TokenType element;
/* Create a new operator handler. */
public OperatorHandler(final TokenType element) {
this.element = element;
}
@Override
public ConstructorState<TokenType> apply(final ConstructorState<TokenType> pair) {
/*
* Replace the current AST with the result of handling an operator
*/
return new ConstructorState<>(
pair.bindLeft(queuedASTs -> handleOperator(queuedASTs)));
}
private ConstructorState<TokenType>
handleOperator(final Deque<ITree<TokenType>> queuedASTs) {
/*
* The AST we're going to hand back
*/
ITree<TokenType> newAST;
/*
* Handle special operators
*/
if (isSpecialOperator.test(element)) {
newAST = handleSpecialOperator.apply(element).apply(queuedASTs);
} else {
/*
* Error if we don't have enough for a binary operator
*/
if (queuedASTs.size() < 2) {
final String msg = String.format(
"Attempted to parse binary operator without enough operands\n\tProblem operator is: %s\n\tPossible operand is: %s",
element.toString(), queuedASTs.peek().toString());
throw new IllegalStateException(msg);
}
/*
* Grab the two operands
*/
final ITree<TokenType> right = queuedASTs.pop();
final ITree<TokenType> left = queuedASTs.pop();
/*
* Create a new AST
*/
newAST = new Tree<>(element, left, right);
}
/*
* Stick it onto the stack
*/
queuedASTs.push(newAST);
/*
* Hand back the state
*/
return new ConstructorState<>(queuedASTs, newAST);
}
}
/* The initial state of the transformer. */
private final IHolder<ConstructorState<TokenType>> initialState;
/* The predicate tot use to detect operators. */
private final Predicate<TokenType> operatorPredicate;
/* The predicate for detecting special operators. */
private final Predicate<TokenType> isSpecialOperator;
/* The function for handling special operators. */
private final Function<TokenType, QueueFlattener<TokenType>> handleSpecialOperator;
/**
* Create a new transformer
*
* @param initialState
* The initial state of the transformer.
*
* @param operatorPredicate
* The predicate to use to identify operators.
*
* @param isSpecialOperator
* The predicate used to identify special
* operators.
*
* @param handleSpecialOperator
* The function used for handling special
* operators.
*/
public TokenTransformer(final IHolder<ConstructorState<TokenType>> initialState,
final Predicate<TokenType> operatorPredicate,
final Predicate<TokenType> isSpecialOperator,
final Function<TokenType, QueueFlattener<TokenType>> handleSpecialOperator) {
this.initialState = initialState;
this.operatorPredicate = operatorPredicate;
this.isSpecialOperator = isSpecialOperator;
this.handleSpecialOperator = handleSpecialOperator;
}
@Override
public void accept(final TokenType element) {
/*
* Handle operators
*/
if (operatorPredicate.test(element)) {
initialState.transform(new OperatorHandler(element));
} else {
final ITree<TokenType> newAST = new Tree<>(element);
/*
* Insert the new tree into the AST
*/
initialState.transform(pair -> new ConstructorState<>(pair.bindLeft(queue -> {
queue.push(newAST);
return new Pair<>(queue, newAST);
})));
}
}
}
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