Add conditional expression support

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!(),
         }
     }
 

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 {