AC-Boolean 1.0.0 → 1.1.0

raw patch · 2 files changed

+40/−28 lines, 2 filesPVP ok

version bump matches the API change (PVP)

API changes (from Hackage documentation)

Files

• AC-Boolean.cabal +10/−1
• Data/Boolean.hs +30/−27

@@ -1,6 +1,6 @@ Cabal-Version: >= 1.6
 Name:          AC-Boolean
-Version:       1.0.0
+Version:       1.1.0
 Stability:     Experimental
 Synopsis:      Handle Boolean values generatically.
 
@@ -11,6 +11,15 @@   few useful instances. The main benefit is the ability to use
   the usual @&&@, etc. operators without having to invent new
   operator names for every kind of Bool-like thing.
+  .
+  Changes:
+  .
+  * Increase efficiency of @Boolean@ instance for @Bool@.
+  .
+  * Shorten source code.
+  .
+  * Remove function instance. (@Control.Monad.Instances@ provides
+    an equivilent @Monad@ instance.)
 
 Category:      Data, Logic, Math
 License:       BSD3

@@ -6,12 +6,23 @@   names (since the class methods do the same thing, but with more
   general type signatures).
 
-  An interesting consequence of the 'Boolean' instance for monads is
-  that 'P.Maybe' 'P.Bool' is a 'Boolean'. You can use this to implement
-  3-value logic (\"true\", \"false\" and \"other\"), with 'P.Nothing'
-  implementing \"other\". Any logical operations yield 'P.Nothing'
-  unless all arguments are 'P.Just' something. (This is usually the
-  behaviour you want.)
+  Please note the following points:
+
+  * This module imports "Control.Monad.Instances", which brings
+    several new 'P.Monad' instances into scope.
+
+  * Among other things, a monad instance for functions is brought
+    into scope. This, combined with the 'Boolean' instance for
+    monads, causes any function that returns a 'Boolean' to become
+    a 'Boolean' itself. This allows you to write constructions such
+    as @(> 5) && (< 9)@, which has the obvious meaning.
+
+  * Another interesting consequence of the 'Boolean' instance for
+    monads is that 'P.Maybe' 'P.Bool' is a 'Boolean'. You can use
+    this to implement 3-value logic (\"true\", \"false\" and
+    \"other\"), with 'P.Nothing' implementing \"other\". Any logical
+    operations yield 'P.Nothing' unless all arguments are 'P.Just'
+    something. (This is usually the behaviour you want.)
 -}
 
 {-# LANGUAGE FlexibleInstances #-}
@@ -19,6 +30,8 @@ module Data.Boolean where
 
 import qualified Prelude as P
+import qualified Control.Monad as M
+import Control.Monad.Instances -- For the Monad ((->) r) instance.
 
 {- |
   Typeclass for things that have true and false values.
@@ -28,11 +41,11 @@   * Normal 'P.Bool' values (obviously).
 
   * Any function that yields a 'BoolValue' as its result.
-    (For example, 'true' is just a constant function that always
-    returns a truth value, regardless of its input.)
+    (@'true' = 'P.const' 'P.True'@, @'false' = 'P.const' 'P.False'@)
+    This instance arrises due to the monad instance for functions.
 
   * Any monadic action that yields a 'BoolValue' as its result.
-    (This is just 'P.return' applied to the appropriate 'BoolValue'.)
+    (@'true' = 'P.return' 'P.True'@, @'false' = 'P.return' 'P.False'@)
 -}
 class BoolValue b where
   true  :: b
@@ -42,10 +55,6 @@   true  = P.True
   false = P.False
 
-instance (BoolValue b) => BoolValue (x -> b) where
-  true  = \ _ -> true
-  false = \ _ -> false
-
 instance (P.Monad m, BoolValue b) => BoolValue (m b) where
   true  = P.return true
   false = P.return false
@@ -62,12 +71,11 @@   * Normal 'P.Bool' values (obviously).
 
   * Any function that returns a 'Boolean'.
-    (The result is a new function that runs the old function(s) and
-    applies the appropriate operator to the result(s).)
+    This instance arrises due to the monad instance for functions.
 
   * Any monadic action that returns a 'Boolean'.
-    (Again, the result is a new action that runs the existing
-    action(s) and applies the appropriate operator to the result(s).)
+    The left action is performed before the right action (which may
+    be significant, depending on the monad).
 -}
 class Boolean b where
   -- | Logical-AND of two values.
@@ -91,15 +99,10 @@   (&&) = (P.&&)
   (||) = (P.||)
   not  = P.not
-
-instance (Boolean b) => Boolean (x -> b) where
-  f && g = \ x -> f x && g x
-  f || g = \ x -> f x || g x
-  not f  = \ x -> not (f x)
-  f `xor` g = \ x -> (f x) `xor` (g x)
+  xor  = (P.==)
 
 instance (P.Monad m, Boolean b) => Boolean (m b) where
-  f && g = f P.>>= \ x -> g P.>>= \ y -> P.return (x && y)
-  f || g = f P.>>= \ x -> g P.>>= \ y -> P.return (x || y)
-  not f  = f P.>>= \ x -> P.return (not x)
-  f `xor` g = f P.>>= \ x -> g P.>>= \ y -> P.return (x `xor` y)
+  (&&) = M.liftM2 (&&)
+  (||) = M.liftM2 (||)
+  not  = M.liftM  not
+  xor  = M.liftM2 xor