X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Flib%2Fstd%2FRatio.lhs;h=dd18de3aa60d06f9b98b34768a02ee923695c8d0;hb=5d25aa0135bf17da82dd27f23f518b513c9252d9;hp=02e32e3a861fc3e2878a13669664ae37e66a8632;hpb=438596897ebbe25a07e1c82085cfbc5bdb00f09e;p=ghc-hetmet.git

diff --git a/ghc/lib/std/Ratio.lhs b/ghc/lib/std/Ratio.lhs
index 02e32e3..dd18de3 100644
--- a/ghc/lib/std/Ratio.lhs
+++ b/ghc/lib/std/Ratio.lhs
@@ -1,5 +1,7 @@
+% ------------------------------------------------------------------------------
+% $Id: Ratio.lhs,v 1.7 2000/06/30 13:39:36 simonmar Exp $
 %
-% (c) The AQUA Project, Glasgow University, 1994-1996
+% (c) The University of Glasgow, 1994-2000
 %
 
 \section[Ratio]{Module @Ratio@}
@@ -7,14 +9,89 @@
 Standard functions on rational numbers
 
 \begin{code}
-{-# OPTIONS -fno-implicit-prelude #-}
+module	Ratio
+    ( Ratio
+    , Rational
+    , (%)		-- :: (Integral a) => a -> a -> Ratio a
+    , numerator		-- :: (Integral a) => Ratio a -> a
+    , denominator	-- :: (Integral a) => Ratio a -> a
+    , approxRational	-- :: (RealFrac a) => a -> a -> Rational
+
+    -- Ratio instances: 
+    --   (Integral a) => Eq   (Ratio a)
+    --   (Integral a) => Ord  (Ratio a)
+    --   (Integral a) => Num  (Ratio a)
+    --   (Integral a) => Real (Ratio a)
+    --   (Integral a) => Fractional (Ratio a)
+    --   (Integral a) => RealFrac (Ratio a)
+    --   (Integral a) => Enum	  (Ratio a)
+    --   (Read a, Integral a) => Read (Ratio a)
+    --   (Integral a) => Show	  (Ratio a)
+    --
+    -- Implementation checked wrt. Haskell 98 lib report, 1/99.
 
-module	Ratio (
-    Ratio, Rational, (%), numerator, denominator, approxRational
   ) where
+\end{code}
+
+
+#ifndef __HUGS__
+
+\begin{code}
+import Prelude		-- To generate the dependencies
+import PrelReal		-- The basic defns for Ratio
+\end{code}
+
+%*********************************************************
+%*							*
+\subsection{approxRational}
+%*							*
+%*********************************************************
+
+@approxRational@, applied to two real fractional numbers x and epsilon,
+returns the simplest rational number within epsilon of x.  A rational
+number n%d in reduced form is said to be simpler than another n'%d' if
+abs n <= abs n' && d <= d'.  Any real interval contains a unique
+simplest rational; here, for simplicity, we assume a closed rational
+interval.  If such an interval includes at least one whole number, then
+the simplest rational is the absolutely least whole number.  Otherwise,
+the bounds are of the form q%1 + r%d and q%1 + r'%d', where abs r < d
+and abs r' < d', and the simplest rational is q%1 + the reciprocal of
+the simplest rational between d'%r' and d%r.
+
+\begin{code}
+approxRational		:: (RealFrac a) => a -> a -> Rational
+approxRational rat eps	=  simplest (rat-eps) (rat+eps)
+	where simplest x y | y < x	=  simplest y x
+			   | x == y	=  xr
+			   | x > 0	=  simplest' n d n' d'
+			   | y < 0	=  - simplest' (-n') d' (-n) d
+			   | otherwise	=  0 :% 1
+					where xr  = toRational x
+					      n   = numerator xr
+					      d   = denominator xr
+					      nd' = toRational y
+					      n'  = numerator nd'
+					      d'  = denominator nd'
+
+	      simplest' n d n' d'	-- assumes 0 < n%d < n'%d'
+			| r == 0     =	q :% 1
+			| q /= q'    =	(q+1) :% 1
+			| otherwise  =	(q*n''+d'') :% n''
+				     where (q,r)      =	 quotRem n d
+					   (q',r')    =	 quotRem n' d'
+					   nd''       =  simplest' d' r' d r
+					   n''        =  numerator nd''
+					   d''        =	 denominator nd''
 
-import PrelNum
-import PrelNumExtra
 \end{code}
 
+#else
+
+\begin{code}
+-- Hugs already has this functionally inside its prelude
+\end{code}
+
+#endif
+
+