diff --git a/src/org/nwapw/abacus/tree/FunctionNode.java b/src/org/nwapw/abacus/tree/FunctionNode.java
new file mode 100644
index 0000000..bd82d38
--- /dev/null
+++ b/src/org/nwapw/abacus/tree/FunctionNode.java
@@ -0,0 +1,47 @@
+package org.nwapw.abacus.tree;
+
+import java.util.ArrayList;
+
+public class FunctionNode extends TreeNode {
+
+    private String function;
+    private ArrayList<TreeNode> children;
+
+    private FunctionNode() { }
+
+    public FunctionNode(String function){
+        this.function = function;
+        children = new ArrayList<>();
+    }
+
+    public String getFunction() {
+        return function;
+    }
+
+    public void addChild(TreeNode node){
+        children.add(node);
+    }
+
+    @Override
+    public <T> T reduce(Reducer<T> reducer) {
+        Object[] reducedChildren = new Object[children.size()];
+        for(int i = 0; i < reducedChildren.length; i++){
+            reducedChildren[i] = children.get(i).reduce(reducer);
+            if(reducedChildren[i] == null) return null;
+        }
+        return reducer.reduceNode(this, reducedChildren);
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder buffer = new StringBuilder();
+        buffer.append(function);
+        buffer.append("(");
+        for(int i = 0; i < children.size(); i++){
+            buffer.append(children.get(i));
+            buffer.append(i == children.size() - 1 ? "" : ", ");
+        }
+        buffer.append(")");
+        return buffer.toString();
+    }
+}
diff --git a/src/org/nwapw/abacus/tree/TokenType.java b/src/org/nwapw/abacus/tree/TokenType.java
index ce92eb3..06301ae 100644
--- a/src/org/nwapw/abacus/tree/TokenType.java
+++ b/src/org/nwapw/abacus/tree/TokenType.java
@@ -6,7 +6,7 @@ package org.nwapw.abacus.tree;
  */
 public enum TokenType {
 
-    ANY(0), OP(1), NUM(2), WORD(3), OPEN_PARENTH(4), CLOSE_PARENTH(5);
+    INTERNAL_FUNCTION_END(-1), INTERNAL_FUNCTION_START(-1), ANY(0), COMMA(1), OP(2), NUM(3), WORD(4), OPEN_PARENTH(5), CLOSE_PARENTH(6);
 
     /**
      * The priority by which this token gets sorted.
diff --git a/src/org/nwapw/abacus/tree/TreeNode.java b/src/org/nwapw/abacus/tree/TreeNode.java
index accdefa..f028274 100644
--- a/src/org/nwapw/abacus/tree/TreeNode.java
+++ b/src/org/nwapw/abacus/tree/TreeNode.java
@@ -14,6 +14,7 @@ public abstract class TreeNode {
      * The lexer used to lex tokens.
      */
     protected static Lexer<TokenType> lexer = new Lexer<TokenType>(){{
+        register(",", TokenType.COMMA);
         register("\\+|-|\\*|/|^", TokenType.OP);
         register("[0-9]+(\\.[0-9]+)?", TokenType.NUM);
         register("[a-zA-Z]+", TokenType.WORD);
@@ -67,9 +68,10 @@ public abstract class TreeNode {
         Stack<Match<TokenType>> tokenStack = new Stack<>();
         while(!from.isEmpty()){
             Match<TokenType> match = from.remove(0);
-            if(match.getType() == TokenType.NUM) {
+            TokenType matchType = match.getType();
+            if(matchType == TokenType.NUM || matchType == TokenType.WORD) {
                 output.add(match);
-            } else if(match.getType() == TokenType.OP){
+            } else if(matchType == TokenType.OP){
                 String tokenString = source.substring(match.getFrom(), match.getTo());
                 int precedence = precedenceMap.get(tokenString);
                 OperatorAssociativity associativity = associativityMap.get(tokenString);
@@ -86,14 +88,24 @@ public abstract class TreeNode {
                     output.add(tokenStack.pop());
                 }
                 tokenStack.push(match);
-            } else if(match.getType() == TokenType.OPEN_PARENTH){
+            } else if(matchType == TokenType.OPEN_PARENTH){
+                if(!output.isEmpty() && output.get(output.size() - 1).getType() == TokenType.WORD){
+                    tokenStack.push(output.remove(output.size() - 1));
+                    output.add(new Match<>(0, 0, TokenType.INTERNAL_FUNCTION_END));
+                }
                 tokenStack.push(match);
-            } else if(match.getType() == TokenType.CLOSE_PARENTH){
+            } else if(matchType == TokenType.CLOSE_PARENTH || matchType == TokenType.COMMA){
                 while(!tokenStack.empty() && tokenStack.peek().getType() != TokenType.OPEN_PARENTH){
                     output.add(tokenStack.pop());
                 }
                 if(tokenStack.empty()) return null;
-                tokenStack.pop();
+                if(matchType == TokenType.CLOSE_PARENTH){
+                    tokenStack.pop();
+                    if(!tokenStack.empty() && tokenStack.peek().getType() == TokenType.WORD) {
+                        output.add(tokenStack.pop());
+                        output.add(new Match<>(0, 0, TokenType.INTERNAL_FUNCTION_START));
+                    }
+                }
             }
         }
         while(!tokenStack.empty()){
@@ -119,6 +131,19 @@ public abstract class TreeNode {
             else return new OpNode(source.substring(match.getFrom(), match.getTo()), left, right);
         } else if(match.getType() == TokenType.NUM){
             return new NumberNode(Double.parseDouble(source.substring(match.getFrom(), match.getTo())));
+        } else if(match.getType() == TokenType.INTERNAL_FUNCTION_START){
+            if(matches.isEmpty() || matches.get(0).getType() != TokenType.WORD) return null;
+            Match<TokenType> stringName = matches.remove(0);
+            String functionName = source.substring(stringName.getFrom(), stringName.getTo());
+            FunctionNode node = new FunctionNode(functionName);
+            while(!matches.isEmpty() && matches.get(0).getType() != TokenType.INTERNAL_FUNCTION_END){
+                TreeNode argument = fromStringRecursive(source, matches);
+                if(argument == null) return null;
+                node.addChild(argument);
+            }
+            if(matches.isEmpty()) return null;
+            matches.remove(0);
+            return node;
         }
         return null;
     }