[project @ 2003-12-22 12:41:52 by simonmar]

[ghc-base.git] / GHC / Real.lhs

diff --git a/GHC/Real.lhs b/GHC/Real.lhs
index 0c27ce3..edee350 100644 (file)
--- a/GHC/Real.lhs
+++ b/GHC/Real.lhs
@@ -1,25 +1,19 @@
-% ------------------------------------------------------------------------------
-% $Id: Real.lhs,v 1.2 2001/12/21 15:07:25 simonmar Exp $
-%
-% (c) The University of Glasgow, 1994-2000
-%
-
-\section[GHC.Real]{Module @GHC.Real@}
-
-The types
-
-       Ratio, Rational
-
-and the classes
-
-       Real
-       Integral
-       Fractional
-       RealFrac
-
-
 \begin{code}
 {-# OPTIONS -fno-implicit-prelude #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  GHC.Real
+-- Copyright   :  (c) The FFI Task Force, 1994-2002
+-- License     :  see libraries/base/LICENSE
+-- 
+-- Maintainer  :  cvs-ghc@haskell.org
+-- Stability   :  internal
+-- Portability :  non-portable (GHC Extensions)
+--
+-- The types 'Ratio' and 'Rational', and the classes 'Real', 'Fractional',
+-- 'Integral', and 'RealFrac'.
+--
+-----------------------------------------------------------------------------
 
 module GHC.Real where
 
@@ -32,6 +26,7 @@ import GHC.Show
 
 infixr 8  ^, ^^
 infixl 7  /, `quot`, `rem`, `div`, `mod`
+infixl 7  %
 
 default ()             -- Double isn't available yet, 
                        -- and we shouldn't be using defaults anyway
@@ -46,7 +41,22 @@ default ()           -- Double isn't available yet,
 
 \begin{code}
 data  (Integral a)     => Ratio a = !a :% !a  deriving (Eq)
+
+-- | Arbitrary-precision rational numbers, represented as a ratio of
+-- two 'Integer' values.  A rational number may be constructed using
+-- the '%' operator.
 type  Rational         =  Ratio Integer
+
+ratioPrec, ratioPrec1 :: Int
+ratioPrec  = 7         -- Precedence of ':%' constructor
+ratioPrec1 = ratioPrec + 1
+
+infinity, notANumber :: Rational
+infinity   = 1 :% 0
+notANumber = 0 :% 0
+
+-- Use :%, not % for Inf/NaN; the latter would 
+-- immediately lead to a runtime error, because it normalises. 
 \end{code}
 
 
@@ -144,7 +154,7 @@ numericEnumFromThenTo   :: (Ord a, Fractional a) => a -> a -> a -> [a]
 numericEnumFromThenTo e1 e2 e3 = takeWhile pred (numericEnumFromThen e1 e2)
                                where
                                 mid = (e2 - e1) / 2
-                                pred | e2 > e1   = (<= e3 + mid)
+                                pred | e2 >= e1  = (<= e3 + mid)
                                      | otherwise = (>= e3 + mid)
 \end{code}
 
@@ -162,18 +172,22 @@ instance  Real Int  where
 instance  Integral Int where
     toInteger i = int2Integer i  -- give back a full-blown Integer
 
-    -- Following chks for zero divisor are non-standard (WDP)
-    a `quot` b =  if b /= 0
-                  then a `quotInt` b
-                  else error "Prelude.Integral.quot{Int}: divide by 0"
-    a `rem` b  =  if b /= 0
-                  then a `remInt` b
-                  else error "Prelude.Integral.rem{Int}: divide by 0"
+    a `quot` 0   = divZeroError
+    a `quot` b =  a `quotInt` b
 
-    x `div` y = x `divInt` y
-    x `mod` y = x `modInt` y
+    a `rem` 0   = divZeroError
+    a `rem` b  = a `remInt` b
 
+    a `div` 0   = divZeroError
+    a `div` b   = a `divInt` b
+
+    a `mod` 0   = divZeroError
+    a `mod` b   = a `modInt` b
+
+    a `quotRem` 0 = divZeroError
     a `quotRem` b = a `quotRemInt` b
+
+    a `divMod`  0 = divZeroError
     a `divMod`  b = a `divModInt`  b
 \end{code}
 
@@ -191,14 +205,19 @@ instance  Real Integer  where
 instance  Integral Integer where
     toInteger n             = n
 
+    a `quot` 0 = divZeroError
     n `quot` d = n `quotInteger` d
-    n `rem`  d = n `remInteger`  d
 
-    n `div` d  =  q  where (q,_) = divMod n d
-    n `mod` d  =  r  where (_,r) = divMod n d
+    a `rem` 0 = divZeroError
+    n `rem`  d = n `remInteger`  d
 
+    a `divMod` 0 = divZeroError
     a `divMod` b = a `divModInteger` b
+
+    a `quotRem` 0 = divZeroError
     a `quotRem` b = a `quotRemInteger` b
+
+    -- use the defaults for div & mod
 \end{code}
 
 
@@ -241,11 +260,10 @@ instance  (Integral a)    => RealFrac (Ratio a)  where
 
 instance  (Integral a)  => Show (Ratio a)  where
     {-# SPECIALIZE instance Show Rational #-}
-    showsPrec p (x:%y) =  showParen (p > ratio_prec)
-                              (shows x . showString " % " . shows y)
-
-ratio_prec :: Int
-ratio_prec = 7
+    showsPrec p (x:%y) =  showParen (p > ratioPrec) $
+                          showsPrec ratioPrec1 x . 
+                          showString " % " . 
+                          showsPrec ratioPrec1 y
 
 instance  (Integral a) => Enum (Ratio a)  where
     {-# SPECIALIZE instance Enum Rational #-}
@@ -282,16 +300,6 @@ realToFrac = fromRational . toRational
 {-# RULES
 "realToFrac/Int->Int" realToFrac = id :: Int -> Int
     #-}
-
--- For backward compatibility
-{-# DEPRECATED fromInt "use fromIntegral instead" #-}
-fromInt :: Num a => Int -> a
-fromInt = fromIntegral
-
--- For backward compatibility
-{-# DEPRECATED toInt "use fromIntegral instead" #-}
-toInt :: Integral a => a -> Int
-toInt = fromIntegral
 \end{code}
 
 %*********************************************************