From: Bart Massey <bart@cs.pdx.edu>
Date: Sat, 26 Jul 2008 08:04:44 +0000 (+0000)
Subject: applied patches to make enumFrom and friends strict in arguments as per the Report... 
X-Git-Tag: 6_10_branch_has_been_forked~117
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=e007a7cad7f402caaedacf1933e38b55d744ac4b;p=ghc-base.git

applied patches to make enumFrom and friends strict in arguments as per the Report; closes ticket #1997
---

diff --git a/GHC/Num.lhs b/GHC/Num.lhs
index 46cc03d..c92d03e 100644
--- a/GHC/Num.lhs
+++ b/GHC/Num.lhs
@@ -282,10 +282,13 @@ instance  Enum Integer  where
  #-}
 
 enumDeltaIntegerFB :: (Integer -> b -> b) -> Integer -> Integer -> b
-enumDeltaIntegerFB c x d = x `c` enumDeltaIntegerFB c (x+d) d
+enumDeltaIntegerFB c x d = x `seq` (x `c` enumDeltaIntegerFB c (x+d) d)
 
 enumDeltaInteger :: Integer -> Integer -> [Integer]
-enumDeltaInteger x d = x : enumDeltaInteger (x+d) d
+enumDeltaInteger x d = x `seq` x : enumDeltaInteger (x+d) d
+   -- strict accumulator, as for Int
+   -- so, head (drop 1000000 [1 .. ] works
+   -- patch by Don Stewart <dons@galois.com>                       
 
 enumDeltaToIntegerFB c n x delta lim
   | delta >= 0 = up_fb c n x delta lim
diff --git a/GHC/Real.lhs b/GHC/Real.lhs
index d282058..6d1f6e0 100644
--- a/GHC/Real.lhs
+++ b/GHC/Real.lhs
@@ -201,10 +201,10 @@ These 'numeric' enumerations come straight from the Report
 
 \begin{code}
 numericEnumFrom         :: (Fractional a) => a -> [a]
-numericEnumFrom         =  iterate (+1)
+numericEnumFrom n	=  numericEnumFromThen n (n + 1)
 
 numericEnumFromThen     :: (Fractional a) => a -> a -> [a]
-numericEnumFromThen n m =  iterate (+(m-n)) n
+numericEnumFromThen n m	= n `seq` m `seq` n : numericEnumFromThen m (m+m-n)
 
 numericEnumFromTo       :: (Ord a, Fractional a) => a -> a -> [a]
 numericEnumFromTo n m   = takeWhile (<= m + 1/2) (numericEnumFrom n)