diff --git a/src/eval.rs b/src/eval.rs
index 73bb9b4..47641a7 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -166,7 +166,8 @@ impl Evaluator {
                     self.reduce_binop(op, left, right) //can assume both arguments are maximally reduced
                 }
             },
-            Call(name, args) => self.reduce_call(name, args)
+            Call(name, args) => self.reduce_call(name, args),
+            Conditional(_,_,_) => unimplemented!(),
         }
     }
 
diff --git a/src/parser.rs b/src/parser.rs
index 3fcec92..29b2cf3 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -44,6 +44,7 @@ pub enum Expression {
     Variable(String),
     BinExp(String, Box<Expression>, Box<Expression>),
     Call(String, Vec<Expression>),
+    Conditional(Box<Expression>, Box<Expression>, Option<Box<Expression>>),
 }
 
 impl fmt::Display for ASTNode {