On 01/08/2011 14:15, Simon Peyton-Jones wrote:
It's all regrettably delicate, but I think the simplest thing to do is to write
integer-simple using either case expressions direct, or function definitions
that trivially desugar into case expressions. Ie not this:
xorDigits None (!ds) = ds
xorDigits (!ds) None = ds
xorDigits (Some w1 ds1) (Some w2 ds2) = Some (w1 `xor#` w2) (xorDigits ds1 ds2)
but rather
xorDigits None None = None
xorDigits None ds@(Some _) = ds
xorDigits ds@(Some _) None = ds
xorDigits (Some ..) (Some..) = as before
better to keep it simple than try to make the desugarer a bit more clever ..
but then it'll fall over at the next complication.
We've been here before...
http://www.haskell.org/pipermail/cvs-ghc/2010-November/057697.html
http://www.haskell.org/pipermail/cvs-libraries/2010-December/012569.html
Cheers,
Simon
Simon
| -----Original Message-----
| From: [email protected] [mailto:[email protected]] On Behalf Of Max
| Bolingbroke
| Sent: 01 August 2011 08:55
| To: Simon Peyton-Jones
| Cc: Malcolm Wallace; Chris Dornan; [email protected]
| Subject: Re: integer-simple
|
| On 1 August 2011 08:09, Simon Peyton-Jones<[email protected]> wrote:
|> I'm guessing here, but I bet I know what's going on. If integer-simple uses
|> inexhaustive pattern matching, GHC will generate calls to 'patError' for the
|> missing cases. That in turn generates a dependency on base, which is where
|> patError is defined.
|
| I checked this and you are right. If you build with -O0 you can see
| the failure that Chris describes, because GHC does not eliminate some
| of the patErrors. They come from (e.g.) xorDigits, whose tidied Core
| is:
|
| {{{
| Rec {
| xorDigits_raD
| :: GHC.Integer.Type.Digits
| -> GHC.Integer.Type.Digits -> GHC.Integer.Type.Digits
| [GblId, Arity=2]
| xorDigits_raD =
| \ (ds_dh8 :: GHC.Integer.Type.Digits)
| (ds1_afu :: GHC.Integer.Type.Digits) ->
| let {
| fail_dh9
| :: GHC.Prim.State# GHC.Prim.RealWorld -> GHC.Integer.Type.Digits
| [LclId, Arity=1]
| fail_dh9 =
| \ _ ->
| Control.Exception.Base.patError
| @ GHC.Integer.Type.Digits
|
"libraries/integer-simple/GHC/Integer.hs:(734,1)-(736,79)|function
| GHC.Integer.xorDigits" } in
| case ds_dh8 of wild_X1j {
| GHC.Integer.Type.Some ipv_snV ipv1_snW ->
| case ds1_afu of wild1_X1r {
| GHC.Integer.Type.Some ipv2_snZ ipv3_so0 ->
| case wild_X1j of _ {
| GHC.Integer.Type.Some w1_afw ds2_afx ->
| case wild1_X1r of _ {
| GHC.Integer.Type.Some w2_afy ds3_afz ->
| case xorDigits_raD ds2_afx ds3_afz of tpl1_X5 { __DEFAULT
->
| GHC.Integer.Type.Some (GHC.Prim.xor# w1_afw w2_afy)
tpl1_X5
| };
| GHC.Integer.Type.None -> fail_dh9 GHC.Prim.realWorld#
| };
| GHC.Integer.Type.None -> fail_dh9 GHC.Prim.realWorld#
| };
| GHC.Integer.Type.None -> wild_X1j
| };
| GHC.Integer.Type.None -> ds1_afu
| }
| end Rec }
| }}}
|
| They seem to originate from using bang patterns in the definitions:
|
| {{{
| xorDigits :: Digits -> Digits -> Digits
| xorDigits None (!ds) = ds
| xorDigits (!ds) None = ds
| xorDigits (Some w1 ds1) (Some w2 ds2) = Some (w1 `xor#` w2) (xorDigits ds1
| ds2)
| }}}
|
| Maybe the pattern match desugarer needs to be modified to see that the
| pattern (!x) is irrefutable?
|
| In the short term the workaround is to build the libraries with at least -O.
|
| Max
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