From 6dcd129a10af0034b38bfe843d223c4593deee09 Mon Sep 17 00:00:00 2001
From: Ben Culkin <scorpress@gmail.com>
Date: Thu, 12 Nov 2020 20:05:01 -0500
Subject: Cleanup part 2

---
 .../bjc/utils/parserutils/TreeConstructor.java     | 156 +++++++++++++++++++--
 1 file changed, 145 insertions(+), 11 deletions(-)

(limited to 'base/src/main/java/bjc/utils/parserutils/TreeConstructor.java')

diff --git a/base/src/main/java/bjc/utils/parserutils/TreeConstructor.java b/base/src/main/java/bjc/utils/parserutils/TreeConstructor.java
index 3c7509b..6780768 100644
--- a/base/src/main/java/bjc/utils/parserutils/TreeConstructor.java
+++ b/base/src/main/java/bjc/utils/parserutils/TreeConstructor.java
@@ -2,15 +2,11 @@ package bjc.utils.parserutils;
 
 import java.util.Deque;
 import java.util.LinkedList;
-import java.util.function.Function;
-import java.util.function.Predicate;
-
-import bjc.data.IHolder;
-import bjc.data.IPair;
-import bjc.data.ITree;
-import bjc.data.Identity;
-import bjc.data.Pair;
+import java.util.function.*;
+
+import bjc.data.*;
 import bjc.funcdata.IList;
+import bjc.utils.parserutils.TreeConstructor.*;
 
 /**
  * Creates a parse tree from a postfix expression.
@@ -103,13 +99,14 @@ public class TreeConstructor {
 		/*
 		 * Make sure our parameters are valid
 		 */
-		if (tokens == null)
+		if (tokens == null) {
 			throw new NullPointerException("Tokens must not be null");
-		else if (isOperator == null)
+		} else if (isOperator == null) {
 			throw new NullPointerException("Operator predicate must not be null");
-		else if (isSpecialOperator == null)
+		} else if (isSpecialOperator == null) {
 			throw new NullPointerException(
 					"Special operator determiner must not be null");
+		}
 
 		final ConstructorState<TokenType> cstate
 				= new ConstructorState<>(new LinkedList<>(), null);
@@ -127,3 +124,140 @@ public class TreeConstructor {
 		return initialState.unwrap(ConstructorState::getRight);
 	}
 }
+
+/*
+ * Transform function on tokens
+ */
+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);
+					})
+				)
+			);
+		}
+	}
+}
\ No newline at end of file
-- 
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