Throw an error when comparing two RealFunctions for equality.

Print RealFunctions within angled brackets, i.e. "<RealFunction>".

diff --git a/src/RealFunction.hs b/src/RealFunction.hs
index 6a557a9f0f4d4bdb33df42485d84ae02e57cabe5..14afb910e523a2ba611e7ef3d50317cbbf7ffdb4 100644 (file)
--- a/src/RealFunction.hs
+++ b/src/RealFunction.hs
@@ -11,13 +11,13 @@ type RealFunction a = (a -> Double)
 instance Show (RealFunction a) where
     -- | There is nothing of value that we can display about a
     --   function, so simply print its type.
-    show _ = "RealFunction"
+    show _ = "<RealFunction>"
 
 
 -- | An 'Eq' instance is required to be a 'Num' instance.
 instance Eq (RealFunction a) where
     -- | Nothing else makes sense here; always return 'False'.
-    _ == _ = False
+    _ == _ = error "You can't compare functions for equality."
 
 
 -- | The 'Num' instance for RealFunction allows us to perform