[commit: packages/base] ghc-7.8: Fix build due to missing scanl' (416ef66)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/base

On branch  : ghc-7.8
Link       : http://ghc.haskell.org/trac/ghc/changeset/416ef6644ca26ecbebc8dfa5af1963e47e0b2e06/base

>---------------------------------------------------------------

commit 416ef6644ca26ecbebc8dfa5af1963e47e0b2e06
Author: Austin Seipp <austin at well-typed.com>
Date:   Wed Nov 5 16:07:08 2014 -0600

    Fix build due to missing scanl'
    
    This was sitting in my working tree, and I forgot to commit it. Oops.
    
    This is not exported by Data.List, since it's only needed by 'inits'
    
    Signed-off-by: Austin Seipp <austin at well-typed.com>


>---------------------------------------------------------------

416ef6644ca26ecbebc8dfa5af1963e47e0b2e06
 Data/List.hs | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/Data/List.hs b/Data/List.hs
index 8973464..0b484e0 100644
--- a/Data/List.hs
+++ b/Data/List.hs
@@ -1,5 +1,5 @@
 {-# LANGUAGE Trustworthy #-}
-{-# LANGUAGE CPP, NoImplicitPrelude, MagicHash #-}
+{-# LANGUAGE CPP, NoImplicitPrelude, MagicHash, BangPatterns #-}
 
 -----------------------------------------------------------------------------
 -- |
@@ -754,10 +754,23 @@ groupBy eq (x:xs)       =  (x:ys) : groupBy eq zs
 inits                   :: [a] -> [[a]]
 inits                   = map toListSB . scanl' snocSB emptySB
 {-# NOINLINE inits #-}
+
 -- We do not allow inits to inline, because it plays havoc with Call Arity
 -- if it fuses with a consumer, and it would generally lead to serious
 -- loss of sharing if allowed to fuse with a producer.
 
+-- | A strictly accumulating version of 'scanl'
+{-# NOINLINE [1] scanl' #-}
+scanl'           :: (b -> a -> b) -> b -> [a] -> [b]
+-- This peculiar form is needed to prevent scanl' from being rewritten
+-- in its own right hand side.
+scanl' = scanlGo'
+  where
+    scanlGo' :: (b -> a -> b) -> b -> [a] -> [b]
+    scanlGo' f !q ls    = q : (case ls of
+                            []   -> []
+                            x:xs -> scanlGo' f (f q x) xs)
+
 -- | The 'tails' function returns all final segments of the argument,
 -- longest first.  For example,
 --