1 files changed, 131 insertions, 0 deletions
diff --git a/base/src/main/java/bjc/utils/parserutils/TokenTransformer.java b/base/src/main/java/bjc/utils/parserutils/TokenTransformer.java
new file mode 100644
index 0000000..30ccc5a
--- /dev/null
+++ b/base/src/main/java/bjc/utils/parserutils/TokenTransformer.java
@@ -0,0 +1,131 @@
+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.utils.data.IHolder;
+import bjc.utils.data.ITree;
+import bjc.utils.data.Pair;
+import bjc.utils.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>> {
+		private final TokenType element;
+
+		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 -> {
+				return 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);
+		}
+	}
+
+	private final IHolder<ConstructorState<TokenType>> initialState;
+
+	private final Predicate<TokenType> operatorPredicate;
+
+	private final Predicate<TokenType>				isSpecialOperator;
+	private final Function<TokenType, QueueFlattener<TokenType>>	handleSpecialOperator;
+
+	/*
+	 * Create a new transformer
+	 */
+	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 -> {
+				/*
+				 * Transform the pair, ignoring the current AST in favor of the one consisting of the current element
+				 */
+				return new ConstructorState<>(pair.bindLeft(queue -> {
+					queue.push(newAST);
+
+					return new Pair<>(queue, newAST);
+				}));
+			});
+		}
+	}
+}