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Fix GNFData instance for V1 #20

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Aug 16, 2016
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Fix GNFData instance for V1 #20

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Fix GNFData instance for V1 
Make `grnf` for `V1` a well-defined function that forces its
(bottom) argument rather than making the function itself bottom.

Fixes #19
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@treeowl
treeowl committed Jul 18, 2016
commit 75cac8b89cc1c0de61bcbc06ec0841b0f981c86c
9 changes: 8 additions & 1 deletion Control/DeepSeq.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,9 @@
#if __GLASGOW_HASKELL__ >= 706
{-# LANGUAGE PolyKinds #-}
#endif
#if __GLASGOW_HASKELL__ >= 708
{-# LANGUAGE EmptyCase #-}
#endif
-----------------------------------------------------------------------------
-- |
-- Module : Control.DeepSeq
Expand Down Expand Up @@ -114,7 +117,11 @@ class GNFData f where
grnf :: f a -> ()

instance GNFData V1 where
grnf = error "Control.DeepSeq.rnf: uninhabited type"
#if __GLASGOW_HASKELL__ >= 708
grnf x = case x of {}
#else
grnf !_ = error "Control.DeepSeq.rnf: uninhabited type"
#endif

instance GNFData U1 where
grnf U1 = ()
Expand Down