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author | Simon Peyton Jones <simonpj@microsoft.com> | 2019-01-16 16:34:24 +0000 |
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committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2019-01-22 03:02:20 -0500 |
commit | a5373c1fe172dee31e07bcb7c7f6caff1035e6ba (patch) | |
tree | 35974465290337a66fd6124066e1c1cfe6401ffa /utils | |
parent | 64ce6afa21fadd751e1700af145ab77059abadc6 (diff) | |
download | haskell-a5373c1fe172dee31e07bcb7c7f6caff1035e6ba.tar.gz |
Fix bogus worker for newtypes
The "worker" for a newtype is actually a function
with a small (compulsory) unfolding, namely a cast.
But the construction of this function was plain wrong
for newtype /instances/; it cast the arguemnt to the
family type rather than the representation type.
This never actually bit us because, in the case of a
family instance, we immediately cast the result to
the family type. So we get
\x. (x |> co1) |> co2
where the compositio of co1 and co2 is ill-kinded.
However the optimiser (even the simple optimiser)
just collapsed those casts, ignoring the mis-match
in the middle, so we never saw the problem.
Trac #16191 is indeed a dup of #16141; but the resaon
these tickets produce Lint errors is not the unnecessary
forcing; it's because of the ill-typed casts.
This patch fixes the ill-typed casts, properly. I can't
see a way to trigger an actual failure prior to this
patch, but it's still wrong wrong wrong to have ill-typed
casts, so better to get rid of them.
Diffstat (limited to 'utils')
0 files changed, 0 insertions, 0 deletions