X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=src%2FRealFunction.hs;h=cf98029a5f4948d71375ca0e8c188e19a2d39527;hb=1fbb737e99c620f9ca3acd7d8a455ae57ca45130;hp=834c27a7c0a7fa5b811daeaaa6de1caf5ca62664;hpb=569d6f0f57afccafa5bb4c39e23fcf5e6a77bc03;p=spline3.git

diff --git a/src/RealFunction.hs b/src/RealFunction.hs
index 834c27a..cf98029 100644
--- a/src/RealFunction.hs
+++ b/src/RealFunction.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE FlexibleInstances #-}
 
 module RealFunction
 where
@@ -6,12 +6,22 @@ where
 
 type RealFunction a = (a -> Double)
 
+
+-- | A 'Show' instance is required to be a 'Num' instance.
 instance Show (RealFunction a) where
-    show _ = "Real Function"
+    -- | There is nothing of value that we can display about a
+    --   function, so simply print its type.
+    show _ = "<RealFunction>"
+
 
+-- | An 'Eq' instance is required to be a 'Num' instance.
 instance Eq (RealFunction a) where
-    _ == _ = False
+    -- | Nothing else makes sense here; always return 'False'.
+    _ == _ = error "You can't compare functions for equality."
 
+
+-- | The 'Num' instance for RealFunction allows us to perform
+--   arithmetic on functions in the usual way.
 instance Num (RealFunction a) where
     (f1 + f2)  x = (f1 x) + (f2 x)
     (f1 - f2)  x = (f1 x) - (f2 x)
@@ -22,12 +32,14 @@ instance Num (RealFunction a) where
     fromInteger i _ = fromInteger i
 
 
--- Takes a constant, and a function as arguments. Returns a new
--- function representing the original function times the constant.
+-- | Takes a constant, and a function as arguments. Returns a new
+--   function representing the original function times the constant.
 cmult :: Double -> (RealFunction a) -> (RealFunction a)
 cmult coeff f = (*coeff) . f
 
--- Takes a function f and an exponent n. Returns a new function, f^n.
+
+-- | Takes a function f and an exponent n. Returns a new function,
+--   f^n.
 fexp :: (RealFunction a) -> Int -> (RealFunction a)
 fexp f n
      | n == 0 = (\_ -> 1)