[Fix up isRealValued.
Bryan O'Sullivan <bos@serpentine.com>**20080119012539] {
hunk ./en/ch04-defining-types.xml 563
-      <para id="x_p5">Here, we don't care about the value of the result, just
-	about which constructor was used to create it.  If it was
-	<function>Left</function>, the result must be a complex
-	number, otherwise it must be real.  We can use a wild card for
-	the entire second pattern; there's no need to see if the
-	constructor is <function>Right</function>, because it
-	<emphasis>must</emphasis> be; <type>Either</type> only has two
+      <para id="x_p5">Here, we don't care about the value of the
+	result, just about which constructor was used to create it.
+	If the constructor was <function>Just</function>, the result
+	must be a real number, otherwise it's either infinite or
+	complex.  We can use a wild card for the entire second
+	pattern; there's no need to see if the constructor is
+	<function>Nothing</function>, because it
+	<emphasis>must</emphasis> be; <type>Maybe</type> only has two
hunk ./en/ch04-defining-types.xml 1010
-      <title>Local functions</title>
+      <title>Local functions, global variables</title>
hunk ./examples/ch04/Roots.hs 4
-data Roots = Undefined
-           | RealValued Double Double
-           | ComplexValued (Complex Double) (Complex Double)
+data QuadraticRoots = Undefined
+                    | RealValued Double Double
+                    | ComplexValued (Complex Double) (Complex Double)
hunk ./examples/ch04/Roots.hs 8
-roots :: Double -> Double -> Double -> Roots
+roots :: Double -> Double -> Double -> QuadraticRoots
hunk ./examples/ch04/Roots.hs 26
-isRealValued :: Either (Complex Double, Complex Double) (Double, Double)
-             -> Bool
-isRealValued (Left _) = False
-isRealValued _        = True
+isRealValued :: Maybe (Double, Double) -> Bool
+isRealValued (Just _) = True
+isRealValued _        = False
}