X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FEnum.lhs;h=655b53f363300411ffacddbfdbdb4e3652bfd4d3;hb=e9e2a5412bb7cda8d13a063ac403d9f18ac97380;hp=93af9eb01970a28b2540fe7d9139111682ad9538;hpb=b706340c451952adf230b5b8daecad8a1f34d714;p=ghc-base.git

diff --git a/GHC/Enum.lhs b/GHC/Enum.lhs
index 93af9eb..655b53f 100644
--- a/GHC/Enum.lhs
+++ b/GHC/Enum.lhs
@@ -1,5 +1,5 @@
 \begin{code}
-{-# OPTIONS -fno-implicit-prelude #-}
+{-# OPTIONS_GHC -fno-implicit-prelude #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  GHC.Enum
@@ -36,17 +36,68 @@ default ()		-- Double isn't available yet
 %*********************************************************
 
 \begin{code}
+-- | The 'Bounded' class is used to name the upper and lower limits of a
+-- type.  'Ord' is not a superclass of 'Bounded' since types that are not
+-- totally ordered may also have upper and lower bounds.
+--
+-- The 'Bounded' class may be derived for any enumeration type;
+-- 'minBound' is the first constructor listed in the @data@ declaration
+-- and 'maxBound' is the last.
+-- 'Bounded' may also be derived for single-constructor datatypes whose
+-- constituent types are in 'Bounded'.
+
 class  Bounded a  where
     minBound, maxBound :: a
 
+-- | Class 'Enum' defines operations on sequentially ordered types.
+--
+-- The @enumFrom@... methods are used in Haskell's translation of
+-- arithmetic sequences.
+--
+-- Instances of 'Enum' may be derived for any enumeration type (types
+-- whose constructors have no fields).  The nullary constructors are
+-- assumed to be numbered left-to-right by 'fromEnum' from @0@ through @n-1@.
+-- See Chapter 10 of the /Haskell Report/ for more details.
+--  
+-- For any type that is an instance of class 'Bounded' as well as 'Enum',
+-- the following should hold:
+--
+-- * The calls @'succ' 'maxBound'@ and @'pred' 'minBound'@ should result in
+--   a runtime error.
+-- 
+-- * 'fromEnum' and 'toEnum' should give a runtime error if the 
+--   result value is not representable in the result type.
+--   For example, @'toEnum' 7 :: 'Bool'@ is an error.
+--
+-- * 'enumFrom' and 'enumFromThen' should be defined with an implicit bound,
+--   thus:
+--
+-- >	enumFrom     x   = enumFromTo     x maxBound
+-- >	enumFromThen x y = enumFromThenTo x y bound
+-- >	  where
+-- >	    bound | fromEnum y >= fromEnum x = maxBound
+-- >	          | otherwise                = minBound
+--
 class  Enum a	where
-    succ, pred		:: a -> a
+    -- | the successor of a value.  For numeric types, 'succ' adds 1.
+    succ		:: a -> a
+    -- | the predecessor of a value.  For numeric types, 'pred' subtracts 1.
+    pred		:: a -> a
+    -- | Convert from an 'Int'.
     toEnum              :: Int -> a
+    -- | Convert to an 'Int'.
+    -- It is implementation-dependent what 'fromEnum' returns when
+    -- applied to a value that is too large to fit in an 'Int'.
     fromEnum            :: a -> Int
-    enumFrom		:: a -> [a]		-- [n..]
-    enumFromThen	:: a -> a -> [a]	-- [n,n'..]
-    enumFromTo		:: a -> a -> [a]	-- [n..m]
-    enumFromThenTo	:: a -> a -> a -> [a]	-- [n,n'..m]
+
+    -- | Used in Haskell's translation of @[n..]@.
+    enumFrom		:: a -> [a]
+    -- | Used in Haskell's translation of @[n,n'..]@.
+    enumFromThen	:: a -> a -> [a]
+    -- | Used in Haskell's translation of @[n..m]@.
+    enumFromTo		:: a -> a -> [a]
+    -- | Used in Haskell's translation of @[n,n'..m]@.
+    enumFromThenTo	:: a -> a -> a -> [a]
 
     succ		   = toEnum . (`plusInt` oneInt)  . fromEnum
     pred		   = toEnum . (`minusInt` oneInt) . fromEnum
@@ -81,7 +132,7 @@ instance Bounded () where
     maxBound = ()
 
 instance Enum () where
-    succ _      = error "Prelude.Enum.().succ: bad argment"
+    succ _      = error "Prelude.Enum.().succ: bad argument"
     pred _      = error "Prelude.Enum.().pred: bad argument"
 
     toEnum x | x == zeroInt = ()
@@ -89,9 +140,9 @@ instance Enum () where
 
     fromEnum () = zeroInt
     enumFrom () 	= [()]
-    enumFromThen () () 	= [()]
+    enumFromThen () () 	= let many = ():many in many
     enumFromTo () () 	= [()]
-    enumFromThenTo () () () = [()]
+    enumFromThenTo () () () = let many = ():many in many
 \end{code}
 
 \begin{code}
@@ -122,14 +173,14 @@ instance Bounded Bool where
 
 instance Enum Bool where
   succ False = True
-  succ True  = error "Prelude.Enum.Bool.succ: bad argment"
+  succ True  = error "Prelude.Enum.Bool.succ: bad argument"
 
   pred True  = False
-  pred False  = error "Prelude.Enum.Bool.pred: bad argment"
+  pred False  = error "Prelude.Enum.Bool.pred: bad argument"
 
   toEnum n | n == zeroInt = False
 	   | n == oneInt  = True
-	   | otherwise    = error "Prelude.Enum.Bool.toEnum: bad argment"
+	   | otherwise    = error "Prelude.Enum.Bool.toEnum: bad argument"
 
   fromEnum False = zeroInt
   fromEnum True  = oneInt
@@ -153,16 +204,16 @@ instance Bounded Ordering where
 instance Enum Ordering where
   succ LT = EQ
   succ EQ = GT
-  succ GT = error "Prelude.Enum.Ordering.succ: bad argment"
+  succ GT = error "Prelude.Enum.Ordering.succ: bad argument"
 
   pred GT = EQ
   pred EQ = LT
-  pred LT = error "Prelude.Enum.Ordering.pred: bad argment"
+  pred LT = error "Prelude.Enum.Ordering.pred: bad argument"
 
   toEnum n | n == zeroInt = LT
 	   | n == oneInt  = EQ
 	   | n == twoInt  = GT
-  toEnum _ = error "Prelude.Enum.Ordering.toEnum: bad argment"
+  toEnum _ = error "Prelude.Enum.Ordering.toEnum: bad argument"
 
   fromEnum LT = zeroInt
   fromEnum EQ = oneInt
@@ -326,18 +377,26 @@ instance  Enum Int  where
     {-# INLINE enumFromThenTo #-}
     enumFromThenTo (I# x1) (I# x2) (I# y) = efdtInt x1 x2 y
 
-{-# RULES
-"eftInt"	[~1] forall x y.	eftInt x y	 = build (\ c n -> eftIntFB c n x y)
-"efdInt"	[~1] forall x1 x2.	efdInt x1 x2	 = build (\ c n -> efdIntFB c n x1 x2)
-"efdtInt"	[~1] forall x1 x2 l.	efdtInt x1 x2 l	 = build (\ c n -> efdtIntFB c n x1 x2 l)
 
+-----------------------------------------------------
+-- eftInt and eftIntFB deal with [a..b], which is the 
+-- most common form, so we take a lot of care
+-- In particular, we have rules for deforestation
+
+{-# RULES
+"eftInt"	[~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x y)
 "eftIntList"	[1] eftIntFB  (:) [] = eftInt
-"efdIntList"	[1] efdIntFB  (:) [] = efdInt
-"efdtIntList"	[1] efdtIntFB (:) [] = efdtInt
  #-}
 
+eftInt :: Int# -> Int# -> [Int]
+-- [x1..x2]
+eftInt x y | x ># y    = []
+	   | otherwise = go x
+	       where
+		 go x = I# x : if x ==# y then [] else go (x +# 1#)
 
 {-# INLINE [0] eftIntFB #-}
+eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r
 eftIntFB c n x y | x ># y    = n	
 		 | otherwise = go x
 		 where
@@ -347,66 +406,54 @@ eftIntFB c n x y | x ># y    = n
 	-- so that when eftInfFB is inlined we can inline
 	-- whatver is bound to "c"
 
-eftInt x y | x ># y    = []
-	       | otherwise = go x
-	       where
-		 go x = I# x : if x ==# y then [] else go (x +# 1#)
 
+-----------------------------------------------------
+-- efdInt and efdtInt deal with [a,b..] and [a,b..c], which are much less common
+-- so we are less elaborate.  The code is more complicated anyway, because
+-- of worries about Int overflow, so we don't both with rules and deforestation
 
--- For enumFromThenTo we give up on inlining; so we don't worry
--- about duplicating occurrences of "c"
-{-# NOINLINE [0] efdtIntFB #-}
-efdtIntFB c n x1 x2 y
-  | delta >=# 0# = if x1 ># y then n else go_up_int_fb c n x1 delta lim
-  | otherwise    = if x1 <# y then n else go_dn_int_fb c n x1 delta lim 
-  where
-    delta = x2 -# x1
-    lim   = y -# delta
+efdInt :: Int# -> Int# -> [Int]
+-- [x1,x2..maxInt]
+efdInt x1 x2 
+  | x2 >=# x1 = case maxInt of I# y -> efdtIntUp x1 x2 y
+  | otherwise = case minInt of I# y -> efdtIntDn x1 x2 y
 
+efdtInt :: Int# -> Int# -> Int# -> [Int]
+-- [x1,x2..y]
 efdtInt x1 x2 y
-  | delta >=# 0# = if x1 ># y then [] else go_up_int_list x1 delta lim
-  | otherwise    = if x1 <# y then [] else go_dn_int_list x1 delta lim
-  where
-    delta = x2 -# x1
-    lim   = y -# delta
-
-{-# NOINLINE [0] efdIntFB #-}
-efdIntFB c n x1 x2
-  | delta >=# 0# = case maxInt of I# y -> go_up_int_fb c n x1 delta (y -# delta)
-  | otherwise    = case minInt of I# y -> go_dn_int_fb c n x1 delta (y -# delta)
-  where
-    delta = x2 -# x1
-
-efdInt x1 x2
-  | delta >=# 0# = case maxInt of I# y -> go_up_int_list x1 delta (y -# delta)
-  | otherwise    = case minInt of I# y -> go_dn_int_list x1 delta (y -# delta)
-  where
-    delta = x2 -# x1
-
--- In all of these, the (x +# delta) is guaranteed not to overflow
-
-go_up_int_fb c n x delta lim
-  = go_up x
-  where
-    go_up x | x ># lim  = I# x `c` n
-	    | otherwise = I# x `c` go_up (x +# delta)
-
-go_dn_int_fb c n x delta lim 
-  = go_dn x
-  where
-    go_dn x | x <# lim  = I# x `c` n
-	    | otherwise = I# x `c` go_dn (x +# delta)
-
-go_up_int_list x delta lim
-  = go_up x
-  where
-    go_up x | x ># lim  = [I# x]
-	    | otherwise = I# x : go_up (x +# delta)
-
-go_dn_int_list x delta lim 
-  = go_dn x
-  where
-    go_dn x | x <# lim  = [I# x]
-	    | otherwise = I# x : go_dn (x +# delta)
+  | x2 >=# x1  = efdtIntUp x1 x2 y
+  | otherwise  = efdtIntDn x1 x2 y
+
+efdtIntUp :: Int# -> Int# -> Int# -> [Int]
+efdtIntUp x1 x2 y	-- Be careful about overflow!
+  | y <# x2    = if y <# x1 then [] else [I# x1]
+  | otherwise 
+  = 	-- Common case: x1 < x2 <= y
+    let 
+	delta = x2 -# x1	
+	y' = y -# delta	
+	-- NB: x1 <= y'; hence y' is representable
+
+	-- Invariant: x <= y; and x+delta won't overflow
+        go_up x | x ># y'  = [I# x]
+	        | otherwise = I# x : go_up (x +# delta)
+    in 
+    I# x1 : go_up x2
+  		 	
+efdtIntDn :: Int# -> Int# -> Int# -> [Int]
+efdtIntDn x1 x2 y	-- x2 < x1
+  | y ># x2    = if y ># x1 then [] else [I# x1]
+  | otherwise 
+  = 	-- Common case: x1 > x2 >= y
+    let 
+	delta = x2 -# x1	
+	y' = y -# delta	
+	-- NB: x1 <= y'; hence y' is representable
+
+	-- Invariant: x >= y; and x+delta won't overflow
+        go_dn x | x <# y'  = [I# x]
+	        | otherwise = I# x : go_dn (x +# delta)
+    in 
+    I# x1 : go_dn x2
 \end{code}