TransformListComp accepts invalid unboxed let bindings
Summary
let
bindings with unboxed types in transformed list comprehensions desugar to invalid Core.
Steps to reproduce
{-# language MagicHash, TransformListComp #-}
module TLC where
import GHC.Exts
glum :: [Int] -> [Int]
glum xs = [I# p | I# x <- xs, let p = x +# 3#, then take 3]
This fails Core Lint. With optimizations enabled, it desugars like the following, but it's desugared just as invalidly when optimizations are disabled.
glum :: [Int] -> [Int]
[LclIdX]
glum
= \ (xs_aw5 :: [Int]) ->
build
@Int
(\ (@a_dye) (c_dyf :: Int -> a_dye -> a_dye) (n_dyg :: a_dye) ->
GHC.Base.foldr
@Int#
@a_dye
(\ (ds_dyv :: Int#) (ds_dyu :: a_dye) ->
let {
p_axE :: Int#
[LclId]
p_axE = ds_dyv } in
c_dyf ((\ (ds_dyw :: Int#) -> GHC.Types.I# ds_dyw) p_axE) ds_dyu)
n_dyg
((\ (@a_axU) -> take @a_axU (GHC.Types.I# 3#))
@Int#
(build
@Int#
(\ (@a_dyh) (c_dyi :: Int# -> a_dyh -> a_dyh) (n_dyj :: a_dyh) ->
GHC.Base.foldr
@Int
@a_dyh
(\ (ds_dyl :: Int) (ds_dyk :: a_dyh) ->
case ds_dyl of wild_00 { I# x_axD ->
let {
p_axR :: Int#
[LclId]
p_axR = +# x_axD 3# } in
let {
p_axE :: Int#
[LclId]
p_axE = p_axR } in
c_dyi p_axE ds_dyk
})
n_dyj
xs_aw5))))
end Rec }
Note that one application each of foldr
and build
are at type Int#
, which has the wrong kind.
Expected behavior
I expect this particular example to be rejected by the type checker. However, I would expect the following to continue to work:
loom :: [Int] -> [Int]
loom xs = [z | I# x <- xs, let p = x +# 3#, z <- [1 .. I# p], then take 3]
Note: I've included a "runtime crash" tag even though I haven't written an example that crashes because my informal testing strongly indicates invalid memory accesses that don't happen to segfault.
Environment
- GHC version used:
Optional:
- Operating System:
- System Architecture: