From 1c8bc7132d980c1ff2dbd6b9af579c3b2fd8c63e Mon Sep 17 00:00:00 2001
From: bculkin2442 <bjculkin@mix.wvu.edu>
Date: Sun, 3 Apr 2016 19:22:48 -0400
Subject: General code refactoring and maintenance

---
 .../src/main/java/bjc/utils/parserutils/AST.java   | 179 +++++++++++++--------
 .../utils/parserutils/RuleBasedConfigReader.java   | 110 +++++++++----
 .../java/bjc/utils/parserutils/ShuntingYard.java   | 119 +++++++++-----
 .../bjc/utils/parserutils/TreeConstructor.java     | 151 +++++++++++------
 4 files changed, 373 insertions(+), 186 deletions(-)

(limited to 'BJC-Utils2/src/main/java/bjc/utils/parserutils')

diff --git a/BJC-Utils2/src/main/java/bjc/utils/parserutils/AST.java b/BJC-Utils2/src/main/java/bjc/utils/parserutils/AST.java
index 4bfb469..d5ae3f2 100644
--- a/BJC-Utils2/src/main/java/bjc/utils/parserutils/AST.java
+++ b/BJC-Utils2/src/main/java/bjc/utils/parserutils/AST.java
@@ -17,11 +17,26 @@ import bjc.utils.funcdata.bst.ITreePart.TreeLinearizationMethod;
  *            The type of token in this AST
  */
 public class AST<T> {
-	private T		token;
+	/**
+	 * Indent a string n levels
+	 * 
+	 * @param builder
+	 *            The string to indent
+	 * @param levels
+	 *            The number of levels to indent
+	 */
+	protected static void indentNLevels(StringBuilder builder,
+			int levels) {
+		for (int i = 0; i <= levels; i++) {
+			builder.append("\t");
+		}
+	}
 
 	private AST<T>	left;
 	private AST<T>	right;
 
+	private T		token;
+
 	/**
 	 * Create a new leaf AST node
 	 * 
@@ -52,43 +67,6 @@ public class AST<T> {
 		right = rght;
 	}
 
-	/**
-	 * Traverse an AST
-	 * 
-	 * @param linearizationMethod
-	 *            The way to traverse the tree
-	 * @param action
-	 *            The function to call on each traversed element
-	 */
-	public void traverse(TreeLinearizationMethod linearizationMethod,
-			Consumer<T> action) {
-		if (left != null && right != null) {
-			switch (linearizationMethod) {
-				case INORDER:
-					left.traverse(linearizationMethod, action);
-					action.accept(token);
-					right.traverse(linearizationMethod, action);
-					break;
-				case POSTORDER:
-					left.traverse(linearizationMethod, action);
-					right.traverse(linearizationMethod, action);
-					action.accept(token);
-					break;
-				case PREORDER:
-					action.accept(token);
-					left.traverse(linearizationMethod, action);
-					right.traverse(linearizationMethod, action);
-					break;
-				default:
-					throw new IllegalArgumentException(
-							"Got a invalid tree linearizer "
-									+ linearizationMethod + ". WAT");
-			}
-		} else {
-			action.accept(token);
-		}
-	}
-
 	/**
 	 * Collapse this tree into a single node
 	 * 
@@ -104,11 +82,44 @@ public class AST<T> {
 	 *            The function for transforming the result
 	 * @return The collapsed value of the tree
 	 */
+	@SuppressWarnings("unchecked")
 	public <E, T2> E collapse(Function<T, T2> tokenTransformer,
 			Function<T, BinaryOperator<T2>> nodeTransformer,
 			Function<T2, E> resultTransformer) {
-		return resultTransformer.apply(
-				internalCollapse(tokenTransformer, nodeTransformer));
+		if (tokenTransformer == null) {
+			throw new NullPointerException(
+					"Token transformer must not be null");
+		} else if (nodeTransformer == null) {
+			throw new NullPointerException(
+					"Node transformer must not be null");
+		}
+
+		if (resultTransformer != null) {
+			return resultTransformer.apply(
+					internalCollapse(tokenTransformer, nodeTransformer));
+		} else {
+			// This is valid because if the user passes null as the last
+			// parameter, E will be inferred as Object, but will actually
+			// be T2
+			return (E) internalCollapse(tokenTransformer, nodeTransformer);
+		}
+	}
+
+	/**
+	 * Expand the nodes in an AST
+	 * 
+	 * @param expander
+	 *            The function to use for expanding nodes
+	 * @return The expanded AST
+	 */
+	public AST<T> expand(Function<T, AST<T>> expander) {
+		if (expander == null) {
+			throw new NullPointerException("Expander must not be null");
+		}
+
+		return collapse(expander, (operator) -> (leftAST, rightAST) -> {
+			return new AST<>(operator, leftAST, rightAST);
+		}, null);
 	}
 
 	/*
@@ -129,6 +140,7 @@ public class AST<T> {
 			}
 
 			T2 rightCollapsed;
+
 			if (right == null) {
 				rightCollapsed = null;
 			} else {
@@ -141,15 +153,6 @@ public class AST<T> {
 		}
 	}
 
-	@Override
-	public String toString() {
-		StringBuilder builder = new StringBuilder();
-
-		internalToString(builder, -1);
-
-		return builder.toString();
-	}
-
 	/**
 	 * Internal version of toString for proper rendering
 	 * 
@@ -186,21 +189,6 @@ public class AST<T> {
 		}
 	}
 
-	/**
-	 * Indent a string n levels
-	 * 
-	 * @param builder
-	 *            The string to indent
-	 * @param levels
-	 *            The number of levels to indent
-	 */
-	protected static void indentNLevels(StringBuilder builder,
-			int levels) {
-		for (int i = 0; i <= levels; i++) {
-			builder.append("\t");
-		}
-	}
-
 	/**
 	 * Execute a transform on selective nodes of the tree
 	 * 
@@ -211,6 +199,12 @@ public class AST<T> {
 	 */
 	public void selectiveTransform(Predicate<T> transformerPredicate,
 			UnaryOperator<T> transformer) {
+		if (transformerPredicate == null) {
+			throw new NullPointerException("Predicate must not be null");
+		} else if (transformer == null) {
+			throw new NullPointerException("Transformer must not be null");
+		}
+
 		if (transformerPredicate.test(token)) {
 			token = transformer.apply(token);
 		}
@@ -224,6 +218,15 @@ public class AST<T> {
 		}
 	}
 
+	@Override
+	public String toString() {
+		StringBuilder builder = new StringBuilder();
+
+		internalToString(builder, -1);
+
+		return builder.toString();
+	}
+
 	/**
 	 * Transmute the tokens in an AST into a different sort of token
 	 * 
@@ -235,6 +238,10 @@ public class AST<T> {
 	 * @return The AST with transformed tokens
 	 */
 	public <E> AST<E> transmuteAST(Function<T, E> tokenTransformer) {
+		if (tokenTransformer == null) {
+			throw new NullPointerException("Transformer must not be null");
+		}
+
 		AST<E> leftBranch = null;
 		AST<E> rightBranch = null;
 
@@ -249,4 +256,48 @@ public class AST<T> {
 		return new AST<>(tokenTransformer.apply(token), leftBranch,
 				rightBranch);
 	}
+
+	/**
+	 * Traverse an AST
+	 * 
+	 * @param linearizationMethod
+	 *            The way to traverse the tree
+	 * @param action
+	 *            The function to call on each traversed element
+	 */
+	public void traverse(TreeLinearizationMethod linearizationMethod,
+			Consumer<T> action) {
+		if (linearizationMethod == null) {
+			throw new NullPointerException(
+					"Linearization method must not be null");
+		} else if (action == null) {
+			throw new NullPointerException("Action must not be null");
+		}
+
+		if (left != null && right != null) {
+			switch (linearizationMethod) {
+				case INORDER:
+					left.traverse(linearizationMethod, action);
+					action.accept(token);
+					right.traverse(linearizationMethod, action);
+					break;
+				case POSTORDER:
+					left.traverse(linearizationMethod, action);
+					right.traverse(linearizationMethod, action);
+					action.accept(token);
+					break;
+				case PREORDER:
+					action.accept(token);
+					left.traverse(linearizationMethod, action);
+					right.traverse(linearizationMethod, action);
+					break;
+				default:
+					throw new IllegalArgumentException(
+							"Got a invalid tree linearizer "
+									+ linearizationMethod + ". WAT");
+			}
+		} else {
+			action.accept(token);
+		}
+	}
 }
diff --git a/BJC-Utils2/src/main/java/bjc/utils/parserutils/RuleBasedConfigReader.java b/BJC-Utils2/src/main/java/bjc/utils/parserutils/RuleBasedConfigReader.java
index 46f5f1d..b6162e5 100644
--- a/BJC-Utils2/src/main/java/bjc/utils/parserutils/RuleBasedConfigReader.java
+++ b/BJC-Utils2/src/main/java/bjc/utils/parserutils/RuleBasedConfigReader.java
@@ -2,6 +2,7 @@ package bjc.utils.parserutils;
 
 import java.io.InputStream;
 import java.util.HashMap;
+import java.util.InputMismatchException;
 import java.util.Map;
 import java.util.Scanner;
 import java.util.function.BiConsumer;
@@ -58,6 +59,13 @@ public class RuleBasedConfigReader<E> {
 	 */
 	public void addPragma(String pragmaName,
 			BiConsumer<FunctionalStringTokenizer, E> pragmaAction) {
+		if (pragmaName == null) {
+			throw new NullPointerException("Pragma name must not be null");
+		} else if (pragmaAction == null) {
+			throw new NullPointerException(
+					"Pragma action must not be null");
+		}
+
 		pragmas.put(pragmaName, pragmaAction);
 	}
 
@@ -71,42 +79,77 @@ public class RuleBasedConfigReader<E> {
 	 * @return The final state of the reader
 	 */
 	public E fromStream(InputStream inputStream, E initialState) {
-		Scanner inputSource = new Scanner(inputStream);
-
-		E state = initialState;
-
-		while (inputSource.hasNextLine()) {
-			String line = inputSource.nextLine();
-
-			if (line.equals("")) {
-				endRule.accept(state);
-				continue;
-			} else if (line.startsWith("\t")) {
-				continueRule.accept(new FunctionalStringTokenizer(
-						line.substring(1), " "), state);
-			} else {
-				FunctionalStringTokenizer tokenizer =
-						new FunctionalStringTokenizer(line, " ");
-
-				String nextToken = tokenizer.nextToken();
-				if (nextToken.equals("#")) {
-					// Do nothing, this is a comment
-				} else if (nextToken.equals("pragma")) {
-					String token = tokenizer.nextToken();
-
-					pragmas.getOrDefault(token, (tokenzer, stat) -> {
-						throw new UnknownPragmaException(
-								"Unknown pragma " + token);
-					}).accept(tokenizer, state);
+		if (inputStream == null) {
+			throw new NullPointerException(
+					"Input stream must not be null");
+		}
+
+		E state;
+
+		try (Scanner inputSource = new Scanner(inputStream)) {
+
+			state = initialState;
+			boolean ruleOpen = false;
+			while (inputSource.hasNextLine()) {
+				String line = inputSource.nextLine();
+
+				if (line.equals("")) {
+					if (ruleOpen == false) {
+						// Ignore blank line without an open rule
+					}
+
+					if (endRule == null) {
+						// Nothing happens on rule end
+					} else {
+						endRule.accept(state);
+					}
+
+					continue;
+				} else if (line.startsWith("\t")) {
+					if (ruleOpen == false) {
+						throw new InputMismatchException(
+								"Can't continue rule with no rule currently open");
+					}
+
+					if (continueRule == null) {
+						throw new InputMismatchException(
+								"Attempted to continue rule with rule continuation disabled."
+										+ " Check for extraneous tabs");
+					}
+
+					continueRule.accept(new FunctionalStringTokenizer(
+							line.substring(1), " "), state);
 				} else {
-					startRule.accept(tokenizer,
-							new Pair<>(nextToken, state));
+					FunctionalStringTokenizer tokenizer =
+							new FunctionalStringTokenizer(line, " ");
+
+					String nextToken = tokenizer.nextToken();
+
+					if (nextToken.equals("#") || nextToken.equals("//")) {
+						// Do nothing, this is a comment
+					} else if (nextToken.equals("pragma")) {
+						String token = tokenizer.nextToken();
+
+						pragmas.getOrDefault(token, (tokenzer, stat) -> {
+							throw new UnknownPragmaException(
+									"Unknown pragma " + token);
+						}).accept(tokenizer, state);
+					} else {
+						if (ruleOpen == true) {
+							throw new InputMismatchException(
+									"Attempted to open a"
+											+ " rule with a rule already open. Make sure rules are"
+											+ " seperated by blank lines");
+						}
+
+						startRule.accept(tokenizer,
+								new Pair<>(nextToken, state));
+						ruleOpen = true;
+					}
 				}
 			}
 		}
 
-		inputSource.close();
-
 		return state;
 	}
 
@@ -139,6 +182,11 @@ public class RuleBasedConfigReader<E> {
 	 */
 	public void setStartRule(
 			BiConsumer<FunctionalStringTokenizer, Pair<String, E>> startRule) {
+		if (startRule == null) {
+			throw new NullPointerException(
+					"Action on rule start must be non-null");
+		}
+
 		this.startRule = startRule;
 	}
 }
diff --git a/BJC-Utils2/src/main/java/bjc/utils/parserutils/ShuntingYard.java b/BJC-Utils2/src/main/java/bjc/utils/parserutils/ShuntingYard.java
index 0ca1879..1e5d487 100644
--- a/BJC-Utils2/src/main/java/bjc/utils/parserutils/ShuntingYard.java
+++ b/BJC-Utils2/src/main/java/bjc/utils/parserutils/ShuntingYard.java
@@ -19,42 +19,6 @@ import bjc.utils.funcutils.StringUtils;
  *            The type of tokens being shunted
  */
 public class ShuntingYard<E> {
-
-	private final class TokenShunter implements Consumer<String> {
-		private FunctionalList<E>	output;
-		private Deque<String>		stack;
-		private Function<String, E>	transform;
-
-		public TokenShunter(FunctionalList<E> outpt, Deque<String> stack,
-				Function<String, E> transform) {
-			this.output = outpt;
-			this.stack = stack;
-			this.transform = transform;
-		}
-
-		@Override
-		public void accept(String token) {
-			if (operators.containsKey(token)) {
-				while (!stack.isEmpty()
-						&& isHigherPrec(token, stack.peek())) {
-					output.add(transform.apply(stack.pop()));
-				}
-
-				stack.push(token);
-			} else if (StringUtils.containsOnly(token, "\\(")) {
-				stack.push(token);
-			} else if (StringUtils.containsOnly(token, "\\)")) {
-				while (stack.peek().equals(token.replace(')', '('))) {
-					output.add(transform.apply(stack.pop()));
-				}
-
-				stack.pop();
-			} else {
-				output.add(transform.apply(token));
-			}
-		}
-	}
-
 	/**
 	 * A enum representing the fundamental operator types
 	 * 
@@ -96,6 +60,58 @@ public class ShuntingYard<E> {
 		}
 	}
 
+	private final class TokenShunter implements Consumer<String> {
+		private FunctionalList<E>	output;
+		private Deque<String>		stack;
+		private Function<String, E>	transform;
+
+		public TokenShunter(FunctionalList<E> outpt, Deque<String> stack,
+				Function<String, E> transform) {
+			this.output = outpt;
+			this.stack = stack;
+			this.transform = transform;
+		}
+
+		@Override
+		public void accept(String token) {
+			if (operators.containsKey(token)) {
+				while (!stack.isEmpty()
+						&& isHigherPrec(token, stack.peek())) {
+					output.add(transform.apply(stack.pop()));
+				}
+
+				stack.push(token);
+			} else if (StringUtils.containsOnly(token, "\\(")) {
+				// Handle groups of parenthesis for multiple nesting levels
+				stack.push(token);
+			} else if (StringUtils.containsOnly(token, "\\)")) {
+				// Handle groups of parenthesis for multiple nesting levels
+				while (stack.peek().equals(token.replace(')', '('))) {
+					output.add(transform.apply(stack.pop()));
+				}
+
+				stack.pop();
+			} else {
+				output.add(transform.apply(token));
+			}
+		}
+	}
+
+	private static boolean shouldConfigureBasicOperators = true;
+
+	/**
+	 * Set whether the shunter should configure the four basic math
+	 * operators
+	 * 
+	 * @param configureBasicOperators
+	 *            Whether or not the four basic math operators should be
+	 *            configured
+	 */
+	public static void setBasicOperatorConfiguration(
+			boolean configureBasicOperators) {
+		shouldConfigureBasicOperators = configureBasicOperators;
+	}
+
 	/**
 	 * Holds all the shuntable operations
 	 */
@@ -107,10 +123,12 @@ public class ShuntingYard<E> {
 	public ShuntingYard() {
 		operators = new HashMap<>();
 
-		operators.put("+", Operator.ADD);
-		operators.put("-", Operator.SUBTRACT);
-		operators.put("*", Operator.MULTIPLY);
-		operators.put("/", Operator.DIVIDE);
+		if (shouldConfigureBasicOperators) {
+			operators.put("+", Operator.ADD);
+			operators.put("-", Operator.SUBTRACT);
+			operators.put("*", Operator.MULTIPLY);
+			operators.put("/", Operator.DIVIDE);
+		}
 	}
 
 	/**
@@ -129,13 +147,17 @@ public class ShuntingYard<E> {
 	/**
 	 * Add an operator to the list of shuntable operators
 	 * 
-	 * @param token
+	 * @param operatorToken
 	 *            The token representing the operator
 	 * @param precedence
 	 *            The precedence of the operator
 	 */
-	public void addOp(String token, IPrecedent precedence) {
-		operators.put(token, precedence);
+	public void addOp(String operatorToken, IPrecedent precedence) {
+		if (operatorToken == null) {
+			throw new NullPointerException("Operator must not be null");
+		}
+
+		operators.put(operatorToken, precedence);
 	}
 
 	private boolean isHigherPrec(String operator, String rightOperator) {
@@ -155,7 +177,14 @@ public class ShuntingYard<E> {
 	 */
 	public FunctionalList<E> postfix(FunctionalList<String> input,
 			Function<String, E> tokenTransformer) {
+		if (input == null) {
+			throw new NullPointerException("Input must not be null");
+		} else if (tokenTransformer == null) {
+			throw new NullPointerException("Transformer must not be null");
+		}
+
 		FunctionalList<E> output = new FunctionalList<>();
+
 		Deque<String> stack = new LinkedList<>();
 
 		input.forEach(new TokenShunter(output, stack, tokenTransformer));
@@ -174,6 +203,10 @@ public class ShuntingYard<E> {
 	 *            The token representing the operator
 	 */
 	public void removeOp(String tok) {
+		if (tok == null) {
+			throw new NullPointerException("Token must not be null");
+		}
+
 		operators.remove(tok);
 	}
 }
\ No newline at end of file
diff --git a/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java b/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java
index 42d5a9d..28ca1e3 100644
--- a/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java
+++ b/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java
@@ -2,10 +2,12 @@ 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 bjc.utils.data.GenHolder;
+import bjc.utils.data.IPair;
 import bjc.utils.data.Pair;
 import bjc.utils.funcdata.FunctionalList;
 
@@ -16,6 +18,89 @@ import bjc.utils.funcdata.FunctionalList;
  *
  */
 public class TreeConstructor {
+	private static final class TokenTransformer<T> implements Consumer<T> {
+		private final class OperatorHandler implements
+				Function<IPair<Deque<AST<T>>, AST<T>>, 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) {
+				Deque<AST<T>> queuedASTs =
+						pair.merge((queue, currentAST) -> queue);
+
+				AST<T> mergedAST = pair.merge((queue, currentAST) -> {
+					AST<T> newAST;
+
+					if (isSpecialOperator.test(element)) {
+						newAST = handleSpecialOperator.apply(queue);
+					} else {
+						if (queue.size() < 2) {
+							throw new IllegalStateException(
+									"Attempted to parse binary operator without enough operands");
+						}
+
+						AST<T> rightAST = queue.pop();
+						AST<T> leftAST = queue.pop();
+
+						newAST = new AST<>(element, leftAST, rightAST);
+					}
+
+					queue.push(newAST);
+					return newAST;
+				});
+
+				Pair<Deque<AST<T>>, AST<T>> newPair =
+						new Pair<>(queuedASTs, mergedAST);
+
+				return newPair;
+			}
+		}
+
+		private GenHolder<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(
+				GenHolder<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.apply((Deque<AST<T>> queue) -> {
+						return queue;
+					}, (AST<T> currentAST) -> {
+						return newAST;
+					});
+				});
+			}
+		}
+	}
+
 	/**
 	 * Construct a tree from a list of tokens in postfix notation
 	 * 
@@ -29,10 +114,6 @@ public class TreeConstructor {
 	 *            The predicate to use to determine if something is a
 	 *            operator
 	 * @return A AST from the expression
-	 * 
-	 * @deprecated Use
-	 *             {@link TreeConstructor#constructTree(FunctionalList, Predicate, Predicate, Function)}
-	 *             instead
 	 */
 	public static <T> AST<T> constructTree(FunctionalList<T> tokens,
 			Predicate<T> operatorPredicate) {
@@ -43,7 +124,8 @@ public class TreeConstructor {
 	/**
 	 * Construct a tree from a list of tokens in postfix notation
 	 * 
-	 * Only binary operators are accepted.
+	 * 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
@@ -66,52 +148,25 @@ public class TreeConstructor {
 	public static <T> AST<T> constructTree(FunctionalList<T> tokens,
 			Predicate<T> operatorPredicate, Predicate<T> isSpecialOperator,
 			Function<Deque<AST<T>>, AST<T>> handleSpecialOperator) {
-		GenHolder<Pair<Deque<AST<T>>, AST<T>>> initialState =
-				new GenHolder<>(new Pair<>(new LinkedList<>(), null));
-
-		tokens.forEach((element) -> {
-			if (operatorPredicate.test(element)) {
-				initialState.transform((pair) -> {
-					Deque<AST<T>> queuedASTs =
-							pair.merge((queue, currentAST) -> queue);
-
-					AST<T> mergedAST = pair.merge((queue, currentAST) -> {
-						AST<T> newAST;
-
-						if (isSpecialOperator.test(element)) {
-							newAST = handleSpecialOperator.apply(queue);
-						} else {
-							AST<T> rightAST = queue.pop();
-							AST<T> leftAST = queue.pop();
-
-							newAST = new AST<>(element, leftAST, rightAST);
-						}
+		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");
+		}
 
-						queue.push(newAST);
-						return newAST;
-					});
-
-					Pair<Deque<AST<T>>, AST<T>> newPair =
-							new Pair<>(queuedASTs, mergedAST);
-
-					return newPair;
-				});
-			} else {
-				AST<T> newAST = new AST<>(element);
+		GenHolder<IPair<Deque<AST<T>>, AST<T>>> initialState =
+				new GenHolder<>(new Pair<>(new LinkedList<>(), null));
 
-				initialState.doWith(
-						(pair) -> pair.doWith((queue, currentAST) -> {
-							queue.push(newAST);
-						}));
+		tokens.forEach(
+				new TokenTransformer<>(initialState, operatorPredicate,
+						isSpecialOperator, handleSpecialOperator));
 
-				initialState.transform((pair) -> {
-					return (Pair<Deque<AST<T>>, AST<T>>) pair.apply(
-							(queue) -> queue, (currentAST) -> newAST);
-				});
-			}
+		return initialState.unwrap((pair) -> {
+			return pair.merge((queue, currentAST) -> currentAST);
 		});
-
-		return initialState.unwrap(
-				(pair) -> pair.merge((queue, currentAST) -> currentAST));
 	}
 }
-- 
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