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package bjc.utils.parserutils;
import java.util.Deque;
import java.util.LinkedList;
import java.util.function.Function;
import java.util.function.Predicate;
import bjc.utils.data.IHolder;
import bjc.utils.data.IPair;
import bjc.utils.data.ITree;
import bjc.utils.data.Identity;
import bjc.utils.data.Pair;
import bjc.utils.funcdata.IList;
/**
* Creates a parse tree from a postfix expression.
*
* @author ben
*
*/
public class TreeConstructor {
/**
* Alias interface for special operator types.
*
* @param <TokenType>
* The token type of the tree.
*/
public interface QueueFlattener<TokenType> extends Function<Deque<ITree<TokenType>>, ITree<TokenType>> {
/*
* Alias
*/
}
/* Alias for constructor state. */
static final class ConstructorState<TokenType> extends Pair<Deque<ITree<TokenType>>, ITree<TokenType>> {
public ConstructorState(final Deque<ITree<TokenType>> left, final ITree<TokenType> right) {
super(left, right);
}
public ConstructorState(final IPair<Deque<ITree<TokenType>>, ITree<TokenType>> par) {
super(par.getLeft(), par.getRight());
}
}
/**
* Construct a tree from a list of tokens in postfix notation.
*
* Only binary operators are accepted.
*
* @param <TokenType>
* The elements of the parse tree.
*
* @param tokens
* The list of tokens to build a tree from.
*
* @param isOperator
* The predicate to use to determine if something is a
* operator.
*
* @return A AST from the expression.
*/
public static <TokenType> ITree<TokenType> constructTree(final IList<TokenType> tokens,
final Predicate<TokenType> isOperator) {
/* Construct a tree with no special operators */
return constructTree(tokens, isOperator, 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 <TokenType>
* The elements of the parse tree.
*
* @param tokens
* The list of tokens to build a tree from.
*
* @param isOperator
* 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.
*
*/
public static <TokenType> ITree<TokenType> constructTree(final IList<TokenType> tokens,
final Predicate<TokenType> isOperator, final Predicate<TokenType> isSpecialOperator,
final Function<TokenType, QueueFlattener<TokenType>> handleSpecialOperator) {
/*
* Make sure our parameters are valid
*/
if(tokens == null)
throw new NullPointerException("Tokens must not be null");
else if(isOperator == null)
throw new NullPointerException("Operator predicate must not be null");
else if(isSpecialOperator == null)
throw new NullPointerException("Special operator determiner must not be null");
final ConstructorState<TokenType> cstate = new ConstructorState<>(
new LinkedList<>(), null);
/* Here is the state for the tree construction */
final IHolder<ConstructorState<TokenType>> initialState = new Identity<>(cstate);
/* Transform each of the tokens */
final TokenTransformer trans = new TokenTransformer<>(initialState,
isOperator, isSpecialOperator, handleSpecialOperator);
tokens.forEach(trans);
/* Grab the tree from the state */
return initialState.unwrap(pair -> pair.getRight());
}
}
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