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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