Import GHC.Err so we see bottoming functions properly

Before this patch, GHC/Err.lhs-boot exported divZeroError and overflowError,
as well as plain 'error'.  The latter has a wired-in defn in GHC (MkId.lhs),
but the former two do not.  As a result GHC doesn't see that overflowError
is a bottoming function at a crucial moment when compiling GHC.Real, and
that means that divMod wasn't getting the CPR property.

The fix is easy:
  - GHC/Err.lhs-boot should export only 'error'

  - GHC.Real, GHC.Int, and GHC.Word should import GHC.Err
    directly.  They can do this nowadays without creating
    a module loop, thanks to the new exception story

diff --git a/GHC/Err.lhs-boot b/GHC/Err.lhs-boot
index 0b18d30..9bef80d 100644 (file)
--- a/GHC/Err.lhs-boot
+++ b/GHC/Err.lhs-boot
@@ -4,7 +4,7 @@
 --                  Ghc.Err.hs-boot
 ---------------------------------------------------------------------------
 
-module GHC.Err( error, divZeroError, overflowError ) where
+module GHC.Err( error ) where
 
 -- The type signature for 'error' is a gross hack.
 -- First, we can't give an accurate type for error, because it mentions 
@@ -17,10 +17,4 @@ module GHC.Err( error, divZeroError, overflowError ) where
 -- to mention 'error' so that it gets exported from this .hi-boot
 -- file.
 error    :: a
-
--- divide by zero is needed quite early
-divZeroError :: a
-
--- overflow is needed quite early
-overflowError :: a
 \end{code}

diff --git a/GHC/Int.hs b/GHC/Int.hs
index 2a5b839..ae49806 100644 (file)
--- a/GHC/Int.hs
+++ b/GHC/Int.hs
@@ -37,6 +37,7 @@ import GHC.Num
 import GHC.Real
 import GHC.Read
 import GHC.Arr
+import GHC.Err
 import GHC.Word hiding (uncheckedShiftL64#, uncheckedShiftRL64#)
 import GHC.Show
 

diff --git a/GHC/Real.lhs b/GHC/Real.lhs
index aa00ccb..eca9974 100644 (file)
--- a/GHC/Real.lhs
+++ b/GHC/Real.lhs
@@ -24,6 +24,7 @@ import GHC.Num
 import GHC.List
 import GHC.Enum
 import GHC.Show
+import GHC.Err
 
 infixr 8  ^, ^^
 infixl 7  /, `quot`, `rem`, `div`, `mod`

diff --git a/GHC/Word.hs b/GHC/Word.hs
index 68afadf..8d63e11 100644 (file)
--- a/GHC/Word.hs
+++ b/GHC/Word.hs
@@ -41,6 +41,7 @@ import GHC.Real
 import GHC.Read
 import GHC.Arr
 import GHC.Show
+import GHC.Err
 
 ------------------------------------------------------------------------
 -- Helper functions