Add exponent operator

src/Expr.elm

@@ -8,6 +8,7 @@ type Op
     | Subtract
     | Multiply
     | Divide
+    | Exponent
 
 type Expr 
     = Num Float
@@ -29,6 +30,7 @@ op =
     <|> stringIs "-" Subtract
     <|> stringIs "*" Multiply
     <|> stringIs "/" Divide
+    <|> stringIs "^" Exponent
     |> map Op
 
 group : Parser () Expr

src/Main.elm

@@ -84,6 +84,7 @@ evalRec expr s =
                 Subtract -> binOp (-) s
                 Multiply -> binOp (*) s
                 Divide -> binOp (/) s
+                Exponent -> binOp (^) s
 
 eval : Expr -> Result (List String) (List Float)
 eval e =