diff --git a/core/src/main/java/org/nwapw/abacus/exception/ContextException.java b/core/src/main/java/org/nwapw/abacus/exception/ContextException.java
new file mode 100644
index 0000000..dd2db0e
--- /dev/null
+++ b/core/src/main/java/org/nwapw/abacus/exception/ContextException.java
@@ -0,0 +1,24 @@
+package org.nwapw.abacus.exception;
+
+/**
+ * Exception thrown by the Context in cases where lookup fails
+ * where it should not.
+ */
+public class ContextException extends AbacusException {
+
+    /**
+     * Creates a new ContextException without an extra message.
+     */
+    public ContextException() {
+        this("");
+    }
+
+    /**
+     * Creates a ContextException with the given message.
+     * @param message the message to use.
+     */
+    public ContextException(String message){
+        super("Context exception", message);
+    }
+
+}
diff --git a/core/src/main/java/org/nwapw/abacus/exception/NumberReducerException.java b/core/src/main/java/org/nwapw/abacus/exception/NumberReducerException.java
new file mode 100644
index 0000000..694e0bf
--- /dev/null
+++ b/core/src/main/java/org/nwapw/abacus/exception/NumberReducerException.java
@@ -0,0 +1,25 @@
+package org.nwapw.abacus.exception;
+
+/**
+ * Exception thrown by the NumberReducer if something goes wrong when
+ * transforming a parse tree into a single value.
+ */
+public class NumberReducerException extends AbacusException {
+
+    /**
+     * Creates a new NumberReducerException with
+     * no additional message.
+     */
+    public NumberReducerException() {
+        this("");
+    }
+
+    /**
+     * Creates a new NumberReducerException with the given message.
+     * @param message the message.
+     */
+    public NumberReducerException(String message) {
+        super("Error evaluating expression", message);
+    }
+
+}
diff --git a/core/src/main/java/org/nwapw/abacus/exception/ParseException.java b/core/src/main/java/org/nwapw/abacus/exception/ParseException.java
new file mode 100644
index 0000000..cd394a0
--- /dev/null
+++ b/core/src/main/java/org/nwapw/abacus/exception/ParseException.java
@@ -0,0 +1,23 @@
+package org.nwapw.abacus.exception;
+
+/**
+ * Exception thrown by parsers.
+ */
+public class ParseException extends AbacusException {
+
+    /**
+     * Creates a new ParseException with no additional message.
+     */
+    public ParseException(){
+        this("");
+    }
+
+    /**
+     * Creates a new ParseException with the given additional message.
+     * @param message the message.
+     */
+    public ParseException(String message){
+        super("Failed to parse string", message);
+    }
+
+}
diff --git a/core/src/main/java/org/nwapw/abacus/exception/EvaluationException.java b/core/src/main/java/org/nwapw/abacus/exception/ReductionException.java
similarity index 51%
rename from core/src/main/java/org/nwapw/abacus/exception/EvaluationException.java
rename to core/src/main/java/org/nwapw/abacus/exception/ReductionException.java
index 5eed066..d9173a6 100644
--- a/core/src/main/java/org/nwapw/abacus/exception/EvaluationException.java
+++ b/core/src/main/java/org/nwapw/abacus/exception/ReductionException.java
@@ -1,16 +1,14 @@
 package org.nwapw.abacus.exception;
 
 /**
- * An exception thrown primarily from Tree Value operators and functions,
- * which have to deal with the result of a Reducer as well as the results
- * of Applicable.
+ * An exception thrown from TreeReducers.
  */
-public class EvaluationException extends AbacusException {
+public class ReductionException extends AbacusException {
 
     /**
      * Creates a new EvaluationException with the default string.
      */
-    public EvaluationException() {
+    public ReductionException() {
         this("");
     }
 
@@ -18,7 +16,7 @@ public class EvaluationException extends AbacusException {
      * Creates a new EvaluationError with the given message string.
      * @param message the message string.
      */
-    public EvaluationException(String message) {
+    public ReductionException(String message) {
         super("Evaluation error", message);
     }
 
diff --git a/core/src/main/java/org/nwapw/abacus/exception/TokenizeException.java b/core/src/main/java/org/nwapw/abacus/exception/TokenizeException.java
new file mode 100644
index 0000000..df92ca1
--- /dev/null
+++ b/core/src/main/java/org/nwapw/abacus/exception/TokenizeException.java
@@ -0,0 +1,23 @@
+package org.nwapw.abacus.exception;
+
+/**
+ * Exception thrown by Lexers when they are unable to tokenize the input string.
+ */
+public class TokenizeException extends AbacusException {
+
+    /**
+     * Create a new tokenize exception with no additional data.
+     */
+    public TokenizeException() {
+        this("");
+    }
+
+    /**
+     * Create a new tokenize exception with the given message.
+     * @param message the message to use.
+     */
+    public TokenizeException(String message){
+        super("Failed to tokenize string", message);
+    }
+
+}
diff --git a/core/src/main/java/org/nwapw/abacus/parsing/LexerTokenizer.java b/core/src/main/java/org/nwapw/abacus/parsing/LexerTokenizer.java
index be57744..1096abb 100644
--- a/core/src/main/java/org/nwapw/abacus/parsing/LexerTokenizer.java
+++ b/core/src/main/java/org/nwapw/abacus/parsing/LexerTokenizer.java
@@ -1,5 +1,6 @@
 package org.nwapw.abacus.parsing;
 
+import org.nwapw.abacus.exception.TokenizeException;
 import org.nwapw.abacus.lexing.Lexer;
 import org.nwapw.abacus.lexing.pattern.Match;
 import org.nwapw.abacus.lexing.pattern.Pattern;
@@ -42,7 +43,9 @@ public class LexerTokenizer implements Tokenizer<Match<TokenType>>, PluginListen
 
     @Override
     public List<Match<TokenType>> tokenizeString(String string) {
-        return lexer.lexAll(string, 0, TOKEN_SORTER);
+        List<Match<TokenType>> tokens = lexer.lexAll(string, 0, TOKEN_SORTER);
+        if(tokens == null) throw new TokenizeException();
+        return tokens;
     }
 
     @Override
diff --git a/core/src/main/java/org/nwapw/abacus/parsing/ShuntingYardParser.java b/core/src/main/java/org/nwapw/abacus/parsing/ShuntingYardParser.java
index 611f5c9..f405aa9 100644
--- a/core/src/main/java/org/nwapw/abacus/parsing/ShuntingYardParser.java
+++ b/core/src/main/java/org/nwapw/abacus/parsing/ShuntingYardParser.java
@@ -1,5 +1,6 @@
 package org.nwapw.abacus.parsing;
 
+import org.nwapw.abacus.exception.ParseException;
 import org.nwapw.abacus.function.Operator;
 import org.nwapw.abacus.function.OperatorAssociativity;
 import org.nwapw.abacus.function.OperatorType;
@@ -99,7 +100,7 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
                 while (!tokenStack.empty() && tokenStack.peek().getType() != TokenType.OPEN_PARENTH) {
                     output.add(tokenStack.pop());
                 }
-                if (tokenStack.empty()) return null;
+                if (tokenStack.empty()) throw new ParseException("mismatched parentheses");
                 if (matchType == TokenType.CLOSE_PARENTH) {
                     tokenStack.pop();
                 }
@@ -111,7 +112,7 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
             if (!(newMatchType == TokenType.OP ||
                     newMatchType == TokenType.TREE_VALUE_OP ||
                     newMatchType == TokenType.FUNCTION ||
-                    newMatchType == TokenType.TREE_VALUE_FUNCTION)) return null;
+                    newMatchType == TokenType.TREE_VALUE_FUNCTION)) throw new ParseException("mismatched parentheses");
             output.add(tokenStack.pop());
         }
         return output;
@@ -124,7 +125,7 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
      * @return the construct tree expression.
      */
     public TreeNode constructRecursive(List<Match<TokenType>> matches) {
-        if (matches.size() == 0) return null;
+        if (matches.size() == 0) throw new ParseException("no tokens left in input");
         Match<TokenType> match = matches.remove(0);
         TokenType matchType = match.getType();
         if (matchType == TokenType.OP || matchType == TokenType.TREE_VALUE_OP) {
@@ -133,7 +134,6 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
             if (type == OperatorType.BINARY_INFIX) {
                 TreeNode right = constructRecursive(matches);
                 TreeNode left = constructRecursive(matches);
-                if (left == null || right == null) return null;
                 if (matchType == TokenType.OP) {
                     return new NumberBinaryNode(operator, left, right);
                 } else {
@@ -141,7 +141,6 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
                 }
             } else {
                 TreeNode applyTo = constructRecursive(matches);
-                if (applyTo == null) return null;
                 if (matchType == TokenType.OP) {
                     return new NumberUnaryNode(operator, applyTo);
                 } else {
@@ -157,10 +156,9 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
             List<TreeNode> children = new ArrayList<>();
             while (!matches.isEmpty() && matches.get(0).getType() != TokenType.INTERNAL_FUNCTION_END) {
                 TreeNode argument = constructRecursive(matches);
-                if (argument == null) return null;
                 children.add(0, argument);
             }
-            if (matches.isEmpty()) return null;
+            if (matches.isEmpty()) throw new ParseException("incorrectly formatted function call");
             matches.remove(0);
             CallNode node;
             if (matchType == TokenType.FUNCTION) {
@@ -170,16 +168,17 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
             }
             return node;
         }
-        return null;
+        throw new ParseException("unrecognized token");
     }
 
     @Override
     public TreeNode constructTree(List<Match<TokenType>> tokens) {
+        if (tokens.isEmpty()) throw new ParseException("no input tokens");
         tokens = intoPostfix(new ArrayList<>(tokens));
-        if (tokens == null) return null;
         Collections.reverse(tokens);
         TreeNode constructedTree = constructRecursive(tokens);
-        return tokens.size() == 0 ? constructedTree : null;
+        if(tokens.size() == 0) return constructedTree;
+        throw new ParseException("could not parse all input");
     }
 
     @Override
diff --git a/core/src/main/java/org/nwapw/abacus/parsing/TreeBuilder.java b/core/src/main/java/org/nwapw/abacus/parsing/TreeBuilder.java
index b3d597e..78c2331 100644
--- a/core/src/main/java/org/nwapw/abacus/parsing/TreeBuilder.java
+++ b/core/src/main/java/org/nwapw/abacus/parsing/TreeBuilder.java
@@ -42,9 +42,7 @@ public class TreeBuilder<T> {
      * @return the resulting tree.
      */
     public TreeNode fromString(String input) {
-        List<T> tokens = tokenizer.tokenizeString(input);
-        if (tokens == null) return null;
-        return parser.constructTree(tokens);
+        return parser.constructTree(tokenizer.tokenizeString(input));
     }
 
 }
diff --git a/core/src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java b/core/src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java
index 3d20019..9d95303 100755
--- a/core/src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java
+++ b/core/src/main/java/org/nwapw/abacus/plugin/StandardPlugin.java
@@ -332,7 +332,7 @@ public class StandardPlugin extends Plugin {
             //We'll use the series \sigma_{n >= 1) ((1/3^n + 1/4^n) * 1/n)
             //In the following, a=1/3^n, b=1/4^n, c = 1/n.
             //a is also an error bound.
-            NumberInterface a = implementation.instanceForString("1"), b = a, c = a;
+            NumberInterface a = implementation.instanceForString("1"), b = a, c;
             NumberInterface sum = implementation.instanceForString("0");
             NumberInterface one = implementation.instanceForString("1");
             int n = 0;
@@ -715,7 +715,7 @@ public class StandardPlugin extends Plugin {
      * @return the value of the series
      */
     private static NumberInterface sinTaylor(MutableEvaluationContext context, NumberInterface x) {
-        NumberInterface power = x, multiplier = x.multiply(x).negate(), currentTerm = x, sum = x;
+        NumberInterface power = x, multiplier = x.multiply(x).negate(), currentTerm, sum = x;
         NumberInterface maxError = x.getMaxError();
         int n = 1;
         do {
diff --git a/core/src/main/kotlin/org/nwapw/abacus/Abacus.kt b/core/src/main/kotlin/org/nwapw/abacus/Abacus.kt
index 4b78256..4272aa8 100644
--- a/core/src/main/kotlin/org/nwapw/abacus/Abacus.kt
+++ b/core/src/main/kotlin/org/nwapw/abacus/Abacus.kt
@@ -88,7 +88,7 @@ class Abacus(val configuration: Configuration) {
      * @param input the input string to parse
      * @return the resulting tree, null if the tree builder or the produced tree are null.
      */
-    fun parseString(input: String): TreeNode? = treeBuilder.fromString(input)
+    fun parseString(input: String): TreeNode = treeBuilder.fromString(input)
     /**
      * Evaluates the given tree.
      *
diff --git a/core/src/main/kotlin/org/nwapw/abacus/context/ChainSearchDelegate.kt b/core/src/main/kotlin/org/nwapw/abacus/context/ChainSearchDelegate.kt
index b1245b9..7f4e21a 100644
--- a/core/src/main/kotlin/org/nwapw/abacus/context/ChainSearchDelegate.kt
+++ b/core/src/main/kotlin/org/nwapw/abacus/context/ChainSearchDelegate.kt
@@ -1,5 +1,6 @@
 package org.nwapw.abacus.context
 
+import org.nwapw.abacus.exception.ContextException
 import kotlin.reflect.KProperty
 
 /**
@@ -16,14 +17,14 @@ import kotlin.reflect.KProperty
  */
 class ChainSearchDelegate<out V>(private val valueGetter: EvaluationContext.() -> V?) {
 
-    operator fun getValue(selfRef: Any, property: KProperty<*>): V? {
-        var currentRef = selfRef as? EvaluationContext ?: return null
+    operator fun getValue(selfRef: Any, property: KProperty<*>): V {
+        var currentRef = selfRef as EvaluationContext
         var returnedValue = currentRef.valueGetter()
         while (returnedValue == null) {
             currentRef = currentRef.parent ?: break
             returnedValue = currentRef.valueGetter()
         }
-        return returnedValue
+        return returnedValue ?: throw ContextException("context chain does not contain value")
     }
 
 }
\ No newline at end of file
diff --git a/core/src/main/kotlin/org/nwapw/abacus/context/EvaluationContext.kt b/core/src/main/kotlin/org/nwapw/abacus/context/EvaluationContext.kt
index d4fdadd..293a5ff 100644
--- a/core/src/main/kotlin/org/nwapw/abacus/context/EvaluationContext.kt
+++ b/core/src/main/kotlin/org/nwapw/abacus/context/EvaluationContext.kt
@@ -43,13 +43,13 @@ open class EvaluationContext(val parent: EvaluationContext? = null,
     /**
      * The implementation inherited from this context's parent.
      */
-    val inheritedNumberImplementation: NumberImplementation?
-            by ChainSearchDelegate { numberImplementation}
+    val inheritedNumberImplementation: NumberImplementation
+            by ChainSearchDelegate { numberImplementation }
 
     /**
      * The reducer inherited from this context's parent.
      */
-    val inheritedReducer: Reducer<NumberInterface>?
+    val inheritedReducer: Reducer<NumberInterface>
             by ChainSearchDelegate { reducer }
 
     /**
diff --git a/core/src/main/kotlin/org/nwapw/abacus/tree/NumberReducer.kt b/core/src/main/kotlin/org/nwapw/abacus/tree/NumberReducer.kt
index 7eff50a..1d9885a 100644
--- a/core/src/main/kotlin/org/nwapw/abacus/tree/NumberReducer.kt
+++ b/core/src/main/kotlin/org/nwapw/abacus/tree/NumberReducer.kt
@@ -2,7 +2,8 @@ package org.nwapw.abacus.tree
 
 import org.nwapw.abacus.Abacus
 import org.nwapw.abacus.context.EvaluationContext
-import org.nwapw.abacus.exception.EvaluationException
+import org.nwapw.abacus.exception.NumberReducerException
+import org.nwapw.abacus.exception.ReductionException
 import org.nwapw.abacus.number.NumberInterface
 
 class NumberReducer(val abacus: Abacus, context: EvaluationContext) : Reducer<NumberInterface> {
@@ -17,15 +18,14 @@ class NumberReducer(val abacus: Abacus, context: EvaluationContext) : Reducer<Nu
         val promotionManager = abacus.promotionManager
         return when(treeNode){
             is NumberNode -> {
-                context.inheritedNumberImplementation?.instanceForString(treeNode.number)
-                        ?: throw EvaluationException("no number implementation selected.")
+                context.inheritedNumberImplementation.instanceForString(treeNode.number)
             }
             is VariableNode -> {
                 val variable = context.getVariable(treeNode.variable)
                 if(variable != null) return variable
                 val definition = context.getDefinition(treeNode.variable)
                 if(definition != null) return definition.reduce(this)
-                throw EvaluationException("variable is not defined.")
+                throw NumberReducerException("variable is not defined.")
             }
             is NumberUnaryNode -> {
                 val child = children[0] as NumberInterface
@@ -58,7 +58,7 @@ class NumberReducer(val abacus: Abacus, context: EvaluationContext) : Reducer<Nu
                 abacus.pluginManager.treeValueFunctionFor(treeNode.callTo)
                         .apply(context, *treeNode.children.toTypedArray())
             }
-            else -> throw EvaluationException("unrecognized tree node.")
+            else -> throw ReductionException("unrecognized tree node.")
         }
     }
 
diff --git a/core/src/test/java/org/nwapw/abacus/tests/CalculationTests.java b/core/src/test/java/org/nwapw/abacus/tests/CalculationTests.java
index 1aee10e..b1c0cd4 100755
--- a/core/src/test/java/org/nwapw/abacus/tests/CalculationTests.java
+++ b/core/src/test/java/org/nwapw/abacus/tests/CalculationTests.java
@@ -22,7 +22,6 @@ public class CalculationTests {
 
     private void testOutput(String input, String parseOutput, String output) {
         TreeNode parsedTree = abacus.parseString(input);
-        Assert.assertNotNull(parsedTree);
         Assert.assertEquals(parsedTree.toString(), parseOutput);
         NumberInterface result = abacus.evaluateTree(parsedTree).getValue();
         Assert.assertNotNull(result);
@@ -31,7 +30,6 @@ public class CalculationTests {
 
     private void testDomainException(String input, String parseOutput) {
         TreeNode parsedTree = abacus.parseString(input);
-        Assert.assertNotNull(parsedTree);
         Assert.assertEquals(parsedTree.toString(), parseOutput);
         try {
             abacus.evaluateTree(parsedTree);
diff --git a/fx/src/main/java/org/nwapw/abacus/fx/AbacusController.java b/fx/src/main/java/org/nwapw/abacus/fx/AbacusController.java
index f903618..25f8632 100644
--- a/fx/src/main/java/org/nwapw/abacus/fx/AbacusController.java
+++ b/fx/src/main/java/org/nwapw/abacus/fx/AbacusController.java
@@ -13,11 +13,8 @@ import javafx.util.StringConverter;
 import org.nwapw.abacus.Abacus;
 import org.nwapw.abacus.config.Configuration;
 import org.nwapw.abacus.exception.AbacusException;
-import org.nwapw.abacus.exception.ComputationInterruptedException;
 import org.nwapw.abacus.function.Documentation;
 import org.nwapw.abacus.function.DocumentationType;
-import org.nwapw.abacus.exception.DomainException;
-import org.nwapw.abacus.exception.EvaluationException;
 import org.nwapw.abacus.number.*;
 import org.nwapw.abacus.plugin.ClassFinder;
 import org.nwapw.abacus.plugin.PluginListener;
@@ -145,9 +142,6 @@ public class AbacusController implements PluginListener {
         private String attemptCalculation() {
             try {
                 TreeNode constructedTree = abacus.parseString(inputField.getText());
-                if (constructedTree == null) {
-                    return ERR_SYNTAX;
-                }
                 EvaluationResult result = abacus.evaluateTree(constructedTree);
                 NumberInterface evaluatedNumber = result.getValue();
                 String resultingString = evaluatedNumber.toString();