Refactor to add backtracking support

This probably doesn't help w/ error messages, but it enables some cool
ideas where syntax can be reused in cases where it would otherwise be
invalid

21 files changed, 246 insertions, 80 deletions

diff --git a/JPratt/src/main/java/bjc/pratt/commands/AbstractInitialCommand.java b/JPratt/src/main/java/bjc/pratt/commands/AbstractInitialCommand.java
index 50e884b..48f9ba7 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/AbstractInitialCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/AbstractInitialCommand.java
@@ -21,7 +21,7 @@ import bjc.utils.parserutils.ParserException;
  */
 public abstract class AbstractInitialCommand<K, V, C> implements InitialCommand<K, V, C> {
 	@Override
-	public Tree<Token<K, V>> denote(final Token<K, V> operator,
+	public CommandResult<K, V> denote(final Token<K, V> operator,
 			final ParserContext<K, V, C> ctx) throws ParserException {
 		return intNullDenotation(operator, ctx);
 	}
@@ -39,7 +39,7 @@ public abstract class AbstractInitialCommand<K, V, C> implements InitialCommand<
 	 * @throws ParserException
 	 *                         If something went wrong while parsing.
 	 */
-	protected abstract Tree<Token<K, V>> intNullDenotation(Token<K, V> operator,
+	protected abstract CommandResult<K, V> intNullDenotation(Token<K, V> operator,
 			ParserContext<K, V, C> ctx) throws ParserException;
 
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/BinaryCommand.java b/JPratt/src/main/java/bjc/pratt/commands/BinaryCommand.java
index 069de78..7a65052 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/BinaryCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/BinaryCommand.java
@@ -1,6 +1,7 @@
 package bjc.pratt.commands;
 
 import bjc.pratt.ParserContext;
+import bjc.pratt.commands.CommandResult.Status;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
 import bjc.data.SimpleTree;
@@ -39,12 +40,14 @@ public abstract class BinaryCommand<K, V, C> extends BinaryPostCommand<K, V, C>
 	protected abstract int rightBinding();
 
 	@Override
-	public Tree<Token<K, V>> denote(final Tree<Token<K, V>> operand,
+	public CommandResult<K, V> denote(final Tree<Token<K, V>> operand,
 			final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
-		final Tree<Token<K, V>> opr
+		final CommandResult<K,V> opr
 				= ctx.parse.parseExpression(rightBinding(), ctx.tokens, ctx.state, false);
+		
+		if (opr.status != Status.SUCCESS) return opr;
 
-		return new SimpleTree<>(operator, operand, opr);
+		return CommandResult.success(new SimpleTree<>(operator, operand, opr.success()));
 	}
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/CommandResult.java b/JPratt/src/main/java/bjc/pratt/commands/CommandResult.java
new file mode 100644
index 0000000..d27400f
--- /dev/null
+++ b/JPratt/src/main/java/bjc/pratt/commands/CommandResult.java
@@ -0,0 +1,97 @@
+package bjc.pratt.commands;
+
+import bjc.data.Tree;
+import bjc.pratt.tokens.Token;
+
+/**
+ * Represents the result of executing a command.
+ * 
+ * @author bjcul
+ *
+ * @param <K> The key type of the tokens
+ * @param <V> The value type of the tokens
+ */
+public class CommandResult<K, V> {
+	/**
+	 * Represents the status of a command execution
+	 * 
+	 * @author bjcul
+	 *
+	 */
+	public static enum Status {
+		/**
+		 * The command successfully parsed.
+		 */
+		SUCCESS,
+		/**
+		 * The command failed, in a non-recoverable way
+		 */
+		FAIL,
+		/**
+		 * The command failed. Attempt recovery via backtracking
+		 */
+		BACKTRACK
+	}
+
+	/**
+	 * The status of this command.
+	 */
+	public final Status status;
+	
+	private Tree<Token<K, V>> success;
+	
+	private CommandResult(Status status) {
+		this.status = status;
+	}
+
+	/**
+	 * Get the success value of this command, or null if it failed.
+	 * 
+	 * @return The success value of the command
+	 */
+	public Tree<Token<K, V>> success() {
+		return success;
+	}
+
+	/**
+	 * Create a success result
+	 * 
+	 * @param <K2> The key type of the token
+	 * @param <V2> The value type of the token
+	 * 
+	 * @param succ The tree produced by the command
+	 * 
+	 * @return A command result representing a success
+	 */
+	public static <K2, V2> CommandResult<K2, V2> success(Tree<Token<K2, V2>> succ) {
+		CommandResult<K2, V2> result = new CommandResult<>(Status.SUCCESS);
+		result.success = succ;
+		return result;
+	}
+
+	/**
+	 * Create a non-backtracking failure result.
+	 * 
+	 * @param <K2> The key type of the token
+	 * @param <V2> The value type of the token
+	 * 
+	 * @return A command result representing a non-backtracking fail
+	 */
+	public static <K2, V2> CommandResult<K2, V2> fail() {
+		CommandResult<K2, V2> result = new CommandResult<>(Status.FAIL);
+		return result;
+	}
+
+	/**
+	 * Create a backtracking failure result.
+	 * 
+	 * @param <K2> The key type of the token
+	 * @param <V2> The value type of the token
+	 * 
+	 * @return A command result representing a backtracking fail
+	 */
+	public static <K2, V2> CommandResult<K2, V2> backtrack() {
+		CommandResult<K2, V2> result = new CommandResult<>(Status.BACKTRACK);
+		return result;
+	}
+}
diff --git a/JPratt/src/main/java/bjc/pratt/commands/InitialCommand.java b/JPratt/src/main/java/bjc/pratt/commands/InitialCommand.java
index 3a2a8ff..ba544b4 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/InitialCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/InitialCommand.java
@@ -31,10 +31,10 @@ public interface InitialCommand<K, V, C> {
 	 * @param ctx
 	 *        The context for the command.
 	 *
-	 * @return The tree for this command.
+	 * @return The result of executing the command.
 	 *
 	 * @throws ParserException
 	 *         If something goes wrong during parsing.
 	 */
-	Tree<Token<K, V>> denote(Token<K, V> operator, ParserContext<K, V, C> ctx) throws ParserException;
+	CommandResult<K, V> denote(Token<K, V> operator, ParserContext<K, V, C> ctx) throws ParserException;
 }
diff --git a/JPratt/src/main/java/bjc/pratt/commands/NonInitialCommand.java b/JPratt/src/main/java/bjc/pratt/commands/NonInitialCommand.java
index 12eecb6..02826a9 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/NonInitialCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/NonInitialCommand.java
@@ -32,12 +32,12 @@ public abstract class NonInitialCommand<K, V, C> {
 	 * @param ctx
 	 *        The state needed for commands.
 	 *
-	 * @return The tree this command forms.
+	 * @return The result of executing the command.
 	 *
 	 * @throws ParserException
 	 *         If something went wrong during parsing.
 	 */
-	public abstract Tree<Token<K, V>> denote(Tree<Token<K, V>> operand, Token<K, V> operator,
+	public abstract CommandResult<K, V> denote(Tree<Token<K, V>> operand, Token<K, V> operator,
 			ParserContext<K, V, C> ctx) throws ParserException;
 
 	/**
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/BlockInitialCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/BlockInitialCommand.java
index db11484..1d54996 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/BlockInitialCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/BlockInitialCommand.java
@@ -3,6 +3,7 @@ package bjc.pratt.commands.impls;
 import bjc.pratt.ParserContext;
 import bjc.pratt.blocks.ParseBlock;
 import bjc.pratt.commands.AbstractInitialCommand;
+import bjc.pratt.commands.CommandResult;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
 import bjc.utils.parserutils.ParserException;
@@ -35,7 +36,7 @@ public class BlockInitialCommand<K, V, C> extends AbstractInitialCommand<K, V, C
 	}
 
 	@Override
-	protected Tree<Token<K, V>> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
+	protected CommandResult<K, V> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
 		return blck.parse(ctx);
 	}
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/ChainCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/ChainCommand.java
index ed7a088..7311eb9 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/ChainCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/ChainCommand.java
@@ -4,6 +4,8 @@ import java.util.Set;
 
 import bjc.pratt.ParserContext;
 import bjc.pratt.commands.BinaryPostCommand;
+import bjc.pratt.commands.CommandResult;
+import bjc.pratt.commands.CommandResult.Status;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
 import bjc.data.SimpleTree;
@@ -48,10 +50,12 @@ public class ChainCommand<K, V, C> extends BinaryPostCommand<K, V, C> {
 	}
 
 	@Override
-	public Tree<Token<K, V>> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
+	public CommandResult<K, V> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
 			final ParserContext<K, V, C> ctx) throws ParserException {
-		final Tree<Token<K, V>> tree = ctx.parse.parseExpression(1 + leftBinding(), ctx.tokens, ctx.state,
+		CommandResult<K, V> resOuter = ctx.parse.parseExpression(1 + leftBinding(), ctx.tokens, ctx.state,
 				false);
+		if (resOuter.status != Status.SUCCESS) return resOuter;
+		final Tree<Token<K, V>> tree = resOuter.success();
 
 		final Tree<Token<K, V>> res = new SimpleTree<>(operator, operand, tree);
 
@@ -59,13 +63,16 @@ public class ChainCommand<K, V, C> extends BinaryPostCommand<K, V, C> {
 			final Token<K, V> tok = ctx.tokens.current();
 			ctx.tokens.next();
 
-			final Tree<Token<K, V>> other = denote(tree, tok,
+			CommandResult<K, V> resOther = denote(tree, tok,
 					new ParserContext<>(ctx.tokens, ctx.parse, ctx.state));
+			if (resOther.status != Status.SUCCESS) return resOther;
+			
+			final Tree<Token<K, V>> other = resOther.success();
 
-			return new SimpleTree<>(chain, res, other);
+			return CommandResult.success(new SimpleTree<>(chain, res, other));
 		}
 
-		return res;
+		return CommandResult.success(res);
 	}
 
 	@Override
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/ConstantCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/ConstantCommand.java
index 409adbb..657743c 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/ConstantCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/ConstantCommand.java
@@ -1,6 +1,7 @@
 package bjc.pratt.commands.impls;
 
 import bjc.pratt.ParserContext;
+import bjc.pratt.commands.CommandResult;
 import bjc.pratt.commands.InitialCommand;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
@@ -34,8 +35,8 @@ public class ConstantCommand<K, V, C> implements InitialCommand<K, V, C> {
 	}
 
 	@Override
-	public Tree<Token<K, V>> denote(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
+	public CommandResult<K, V> denote(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
-		return val;
+		return CommandResult.success(val);
 	}
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/DefaultInitialCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/DefaultInitialCommand.java
index 296cb1c..2dfc576 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/DefaultInitialCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/DefaultInitialCommand.java
@@ -1,6 +1,7 @@
 package bjc.pratt.commands.impls;
 
 import bjc.pratt.ParserContext;
+import bjc.pratt.commands.CommandResult;
 import bjc.pratt.commands.InitialCommand;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
@@ -22,7 +23,7 @@ import bjc.utils.parserutils.ParserException;
  */
 public class DefaultInitialCommand<K, V, C> implements InitialCommand<K, V, C> {
 	@Override
-	public Tree<Token<K, V>> denote(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
+	public CommandResult<K, V> denote(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
 		throw new ParserException("Unexpected token " + operator);
 	}
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/DefaultNonInitialCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/DefaultNonInitialCommand.java
index 797473a..2ae9fb7 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/DefaultNonInitialCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/DefaultNonInitialCommand.java
@@ -1,6 +1,7 @@
 package bjc.pratt.commands.impls;
 
 import bjc.pratt.ParserContext;
+import bjc.pratt.commands.CommandResult;
 import bjc.pratt.commands.NonInitialCommand;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
@@ -21,7 +22,7 @@ import bjc.data.Tree;
  */
 public class DefaultNonInitialCommand<K, V, C> extends NonInitialCommand<K, V, C> {
 	@Override
-	public Tree<Token<K, V>> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
+	public CommandResult<K, V> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
 			final ParserContext<K, V, C> ctx) {
 		throw new UnsupportedOperationException("Default command has no left denotation");
 	}
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/DenestingCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/DenestingCommand.java
index fbcd35c..4935c81 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/DenestingCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/DenestingCommand.java
@@ -2,6 +2,8 @@ package bjc.pratt.commands.impls;
 
 import bjc.pratt.ParserContext;
 import bjc.pratt.commands.AbstractInitialCommand;
+import bjc.pratt.commands.CommandResult;
+import bjc.pratt.commands.CommandResult.Status;
 import bjc.pratt.commands.InitialCommand;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
@@ -39,8 +41,10 @@ public class DenestingCommand<K, V, C> extends AbstractInitialCommand<K, V, C> {
 	}
 
 	@Override
-	protected Tree<Token<K, V>> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
+	protected CommandResult<K, V> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
-		return wrapped.denote(operator, ctx).getChild(0);
+		CommandResult<K, V> res = wrapped.denote(operator, ctx);
+		if (res.status != Status.SUCCESS) return res;
+		return CommandResult.success(res.success().getChild(0));
 	}
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/GroupingCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/GroupingCommand.java
index 1515359..44aa2c1 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/GroupingCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/GroupingCommand.java
@@ -3,6 +3,7 @@ package bjc.pratt.commands.impls;
 import bjc.pratt.ParserContext;
 import bjc.pratt.blocks.ParseBlock;
 import bjc.pratt.commands.AbstractInitialCommand;
+import bjc.pratt.commands.CommandResult;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
 import bjc.data.SimpleTree;
@@ -43,10 +44,10 @@ public class GroupingCommand<K, V, C> extends AbstractInitialCommand<K, V, C> {
 	}
 
 	@Override
-	protected Tree<Token<K, V>> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
+	protected CommandResult<K, V> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
-		final Tree<Token<K, V>> opr = innerBlock.parse(ctx);
-
-		return new SimpleTree<>(mark, opr);
+		final CommandResult<K,V> resOpr = innerBlock.parse(ctx);
+		Tree<Token<K, V>> opr = resOpr.success();
+		return CommandResult.success(new SimpleTree<>(mark, opr));
 	}
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/InitialCommands.java b/JPratt/src/main/java/bjc/pratt/commands/impls/InitialCommands.java
index 0cfec29..9801788 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/InitialCommands.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/InitialCommands.java
@@ -9,6 +9,7 @@ import java.util.function.UnaryOperator;
 import bjc.pratt.blocks.ParseBlock;
 import bjc.pratt.commands.InitialCommand;
 import bjc.pratt.tokens.Token;
+import bjc.utils.parserutils.ParserException;
 import bjc.data.SimpleTree;
 import bjc.data.Tree;
 
@@ -210,16 +211,6 @@ public class InitialCommands {
 	 * @return A command that implements a panfix operator
 	 */
 	public static <K, V, C> InitialCommand<K, V, C> panfix(final int precedence, final K term, final Token<K, V> marker) {
-		return (operator, ctx) -> {
-			Tree<Token<K,V>> leftSide = ctx.parse.parseExpression(precedence + 1, ctx.tokens, ctx.state, false);
-			ctx.tokens.expect(term);
-			ctx.tokens.next();
-			
-			Tree<Token<K,V>> rightSide = ctx.parse.parseExpression(precedence + 1, ctx.tokens, ctx.state, false);
-			ctx.tokens.expect(term);
-			ctx.tokens.next();
-			
-			return new SimpleTree<>(marker, leftSide, rightSide);
-		};
+		return new PanfixCommand<K, V, C>(marker, term, precedence);
 	}
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/LeafCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/LeafCommand.java
index 1223641..c702323 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/LeafCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/LeafCommand.java
@@ -1,6 +1,7 @@
 package bjc.pratt.commands.impls;
 
 import bjc.pratt.ParserContext;
+import bjc.pratt.commands.CommandResult;
 import bjc.pratt.commands.InitialCommand;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
@@ -23,8 +24,8 @@ import bjc.utils.parserutils.ParserException;
  */
 public class LeafCommand<K, V, C> implements InitialCommand<K, V, C> {
 	@Override
-	public Tree<Token<K, V>> denote(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
+	public CommandResult<K, V> denote(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
-		return new SimpleTree<>(operator);
+		return CommandResult.success(new SimpleTree<>(operator));
 	}
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/PanfixCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/PanfixCommand.java
new file mode 100644
index 0000000..06e69c1
--- /dev/null
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/PanfixCommand.java
@@ -0,0 +1,39 @@
+package bjc.pratt.commands.impls;
+
+import bjc.data.SimpleTree;
+import bjc.data.Tree;
+import bjc.pratt.ParserContext;
+import bjc.pratt.commands.CommandResult;
+import bjc.pratt.commands.InitialCommand;
+import bjc.pratt.commands.CommandResult.Status;
+import bjc.pratt.tokens.Token;
+import bjc.utils.parserutils.ParserException;
+
+public final class PanfixCommand<K, V, C> implements InitialCommand<K, V, C> {
+	private final Token<K, V> marker;
+	private final K term;
+	private final int precedence;
+
+	public PanfixCommand(Token<K, V> marker, K term, int precedence) {
+		this.marker = marker;
+		this.term = term;
+		this.precedence = precedence;
+	}
+
+	@Override
+	public CommandResult<K, V> denote(Token<K, V> operator, ParserContext<K, V, C> ctx) throws ParserException {
+		CommandResult<K,V> resLeftSide = ctx.parse.parseExpression(precedence + 1, ctx.tokens, ctx.state, false);
+		if (resLeftSide.status != Status.SUCCESS) return resLeftSide;
+		Tree<Token<K, V>> leftSide = resLeftSide.success();
+		ctx.tokens.expect(term);
+		ctx.tokens.next();
+		
+		CommandResult<K, V> resRightSide = ctx.parse.parseExpression(precedence + 1, ctx.tokens, ctx.state, false);
+		if (resLeftSide.status != Status.SUCCESS) return resRightSide;
+		Tree<Token<K,V>> rightSide = resRightSide.success();
+		ctx.tokens.expect(term);
+		ctx.tokens.next();
+		
+		return CommandResult.success(new SimpleTree<>(marker, leftSide, rightSide));
+	}
+}
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/PostCircumfixCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/PostCircumfixCommand.java
index 78ac1ef..ec2c8fb 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/PostCircumfixCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/PostCircumfixCommand.java
@@ -3,6 +3,8 @@ package bjc.pratt.commands.impls;
 import bjc.pratt.ParserContext;
 import bjc.pratt.blocks.ParseBlock;
 import bjc.pratt.commands.BinaryPostCommand;
+import bjc.pratt.commands.CommandResult;
+import bjc.pratt.commands.CommandResult.Status;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
 import bjc.data.SimpleTree;
@@ -50,10 +52,11 @@ public class PostCircumfixCommand<K, V, C> extends BinaryPostCommand<K, V, C> {
 	}
 
 	@Override
-	public Tree<Token<K, V>> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
+	public CommandResult<K, V> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
 			final ParserContext<K, V, C> ctx) throws ParserException {
-		final Tree<Token<K, V>> inside = innerBlock.parse(ctx);
-
-		return new SimpleTree<>(mark, operand, inside);
+		final CommandResult<K,V> insideRes = innerBlock.parse(ctx);
+		if (insideRes.status != Status.SUCCESS) return insideRes;
+		Tree<Token<K, V>> inside = insideRes.success();
+		return CommandResult.success(new SimpleTree<>(mark, operand, inside));
 	}
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/PostfixCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/PostfixCommand.java
index da587c1..ff370d0 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/PostfixCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/PostfixCommand.java
@@ -2,6 +2,7 @@ package bjc.pratt.commands.impls;
 
 import bjc.pratt.ParserContext;
 import bjc.pratt.commands.BinaryPostCommand;
+import bjc.pratt.commands.CommandResult;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
 import bjc.data.SimpleTree;
@@ -33,8 +34,8 @@ public class PostfixCommand<K, V, C> extends BinaryPostCommand<K, V, C> {
 	}
 
 	@Override
-	public Tree<Token<K, V>> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
+	public CommandResult<K, V> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
 			final ParserContext<K, V, C> ctx) throws ParserException {
-		return new SimpleTree<>(operator, operand);
+		return CommandResult.success(new SimpleTree<>(operator, operand));
 	}
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/PreTernaryCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/PreTernaryCommand.java
index e315804..5d5cbe1 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/PreTernaryCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/PreTernaryCommand.java
@@ -3,6 +3,8 @@ package bjc.pratt.commands.impls;
 import bjc.pratt.ParserContext;
 import bjc.pratt.blocks.ParseBlock;
 import bjc.pratt.commands.AbstractInitialCommand;
+import bjc.pratt.commands.CommandResult;
+import bjc.pratt.commands.CommandResult.Status;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
 import bjc.data.SimpleTree;
@@ -63,14 +65,19 @@ public class PreTernaryCommand<K, V, C> extends AbstractInitialCommand<K, V, C>
 	}
 
 	@Override
-	protected Tree<Token<K, V>> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
+	protected CommandResult<K, V> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
-		final Tree<Token<K, V>> cond = condBlock.parse(ctx);
+		final CommandResult<K,V> condRes = condBlock.parse(ctx);
+		if (condRes.status != Status.SUCCESS) return condRes;
+		Tree<Token<K, V>> cond = condRes.success();
+		
+		final CommandResult<K,V> op1Res = opblock1.parse(ctx);
+		if (op1Res.status != Status.SUCCESS) return op1Res;
+		Tree<Token<K, V>> op1 = op1Res.success();
 
-		final Tree<Token<K, V>> op1 = opblock1.parse(ctx);
-
-		final Tree<Token<K, V>> op2 = opblock2.parse(ctx);
-
-		return new SimpleTree<>(trm, cond, op1, op2);
+		final CommandResult<K,V> op2Res = opblock2.parse(ctx);
+		if (op2Res.status != Status.SUCCESS) return op2Res;
+		Tree<Token<K, V>> op2 = op2Res.success();
+		return CommandResult.success(new SimpleTree<>(trm, cond, op1, op2));
 	}
 }
\ No newline at end of file
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/TernaryCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/TernaryCommand.java
index 174f6fb..786dfec 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/TernaryCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/TernaryCommand.java
@@ -3,6 +3,8 @@ package bjc.pratt.commands.impls;
 import bjc.pratt.ParserContext;
 import bjc.pratt.blocks.ParseBlock;
 import bjc.pratt.commands.BinaryPostCommand;
+import bjc.pratt.commands.CommandResult;
+import bjc.pratt.commands.CommandResult.Status;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
 import bjc.data.SimpleTree;
@@ -13,14 +15,11 @@ import bjc.utils.parserutils.ParserException;
  *
  * @author bjculkin
  *
- * @param <K>
- *        The key type of the tokens.
+ * @param <K> The key type of the tokens.
  *
- * @param <V>
- *        The value type of the tokens.
+ * @param <V> The value type of the tokens.
  *
- * @param <C>
- *        The state type of the parser.
+ * @param <C> The state type of the parser.
  */
 public class TernaryCommand<K, V, C> extends BinaryPostCommand<K, V, C> {
 	private final ParseBlock<K, V, C> innerBlck;
@@ -32,25 +31,22 @@ public class TernaryCommand<K, V, C> extends BinaryPostCommand<K, V, C> {
 	/**
 	 * Create a new ternary command.
 	 *
-	 * @param precedence
-	 *        The precedence of this operator.
+	 * @param precedence The precedence of this operator.
 	 *
-	 * @param innerBlock
-	 *        The representation of the inner block of the expression.
+	 * @param innerBlock The representation of the inner block of the expression.
 	 *
-	 * @param marker
-	 *        The token to use as the root of the AST node.
+	 * @param marker     The token to use as the root of the AST node.
 	 *
-	 * @param isNonassoc
-	 *        Whether or not the conditional is associative.
+	 * @param isNonassoc Whether or not the conditional is associative.
 	 */
 	public TernaryCommand(final int precedence, final ParseBlock<K, V, C> innerBlock, final Token<K, V> marker,
 			final boolean isNonassoc) {
 		super(precedence);
 
-		if(innerBlock == null)
+		if (innerBlock == null)
 			throw new NullPointerException("Inner block must not be null");
-		else if(marker == null) throw new NullPointerException("Marker must not be null");
+		else if (marker == null)
+			throw new NullPointerException("Marker must not be null");
 
 		innerBlck = innerBlock;
 		mark = marker;
@@ -58,19 +54,22 @@ public class TernaryCommand<K, V, C> extends BinaryPostCommand<K, V, C> {
 	}
 
 	@Override
-	public Tree<Token<K, V>> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
+	public CommandResult<K, V> denote(final Tree<Token<K, V>> operand, final Token<K, V> operator,
 			final ParserContext<K, V, C> ctx) throws ParserException {
-		final Tree<Token<K, V>> inner = innerBlck.parse(ctx);
-
-		final Tree<Token<K, V>> outer = ctx.parse.parseExpression(1 + leftBinding(), ctx.tokens, ctx.state,
-				false);
-
-		return new SimpleTree<>(mark, inner, operand, outer);
+		final CommandResult<K, V> innerRes = innerBlck.parse(ctx);
+		if (innerRes.status != Status.SUCCESS) return innerRes;
+		Tree<Token<K, V>> inner = innerRes.success();
+		
+		final CommandResult<K,V> outerRes = ctx.parse.parseExpression(1 + leftBinding(), ctx.tokens, ctx.state, false);
+		if (outerRes.status != Status.SUCCESS) return outerRes;
+		Tree<Token<K, V>> outer = outerRes.success();
+		return CommandResult.success(new SimpleTree<>(mark, inner, operand, outer));
 	}
 
 	@Override
 	public int nextBinding() {
-		if(nonassoc) return leftBinding() - 1;
+		if (nonassoc)
+			return leftBinding() - 1;
 
 		return leftBinding();
 	}
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/TransformingInitialCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/TransformingInitialCommand.java
index d39ec90..36f881d 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/TransformingInitialCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/TransformingInitialCommand.java
@@ -4,6 +4,8 @@ import java.util.function.UnaryOperator;
 
 import bjc.pratt.ParserContext;
 import bjc.pratt.commands.AbstractInitialCommand;
+import bjc.pratt.commands.CommandResult;
+import bjc.pratt.commands.CommandResult.Status;
 import bjc.pratt.commands.InitialCommand;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
@@ -45,9 +47,12 @@ public class TransformingInitialCommand<K, V, C> extends AbstractInitialCommand<
 	}
 
 	@Override
-	protected Tree<Token<K, V>> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
+	protected CommandResult<K, V> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
-		return transfrm.apply(internl.denote(operator, ctx));
+		CommandResult<K,V> result = internl.denote(operator, ctx);
+		if (result.status != Status.SUCCESS) return result;
+		
+		return CommandResult.success(transfrm.apply(result.success()));
 	}
 
 }
diff --git a/JPratt/src/main/java/bjc/pratt/commands/impls/UnaryCommand.java b/JPratt/src/main/java/bjc/pratt/commands/impls/UnaryCommand.java
index 2e7365b..657c004 100644
--- a/JPratt/src/main/java/bjc/pratt/commands/impls/UnaryCommand.java
+++ b/JPratt/src/main/java/bjc/pratt/commands/impls/UnaryCommand.java
@@ -2,6 +2,8 @@ package bjc.pratt.commands.impls;
 
 import bjc.pratt.ParserContext;
 import bjc.pratt.commands.AbstractInitialCommand;
+import bjc.pratt.commands.CommandResult;
+import bjc.pratt.commands.CommandResult.Status;
 import bjc.pratt.tokens.Token;
 import bjc.data.Tree;
 import bjc.data.SimpleTree;
@@ -37,10 +39,12 @@ public class UnaryCommand<K, V, C> extends AbstractInitialCommand<K, V, C> {
 	}
 
 	@Override
-	protected Tree<Token<K, V>> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
+	protected CommandResult<K, V> intNullDenotation(final Token<K, V> operator, final ParserContext<K, V, C> ctx)
 			throws ParserException {
-		final Tree<Token<K, V>> opr = ctx.parse.parseExpression(nullPwer, ctx.tokens, ctx.state, false);
+		CommandResult<K,V> result = ctx.parse.parseExpression(nullPwer, ctx.tokens, ctx.state, false);
+		if (result.status != Status.SUCCESS) return result;
+		final Tree<Token<K, V>> opr = result.success();
 
-		return new SimpleTree<>(operator, opr);
+		return CommandResult.success(new SimpleTree<>(operator, opr));
 	}
 }
\ No newline at end of file