GitLab

Consider this program:

{-# LANGUAGE MagicHash, UnboxedTuples #-}
module Main where
import GHC.Exts

f :: (() -> (# Int#, () #)) -> ()
{-# NOINLINE f #-}
-- Strictness signature was (7.8.2)
--    <C(S(LS)), 1*C1(U(A,1*U()))>
-- I.e. calls k, but discards first component of result
f k = case k () of (# _, r #) -> r

g :: Int -> ()
g y = f (\n -> (# case y of I# y2 -> h (h (h (h (h (h (h y2)))))), n #))
   -- RHS is big enough to force worker/wrapper

{-# NOINLINE h #-}
h :: Int# -> Int#
h n = n +# 1#

main = print (g 1)

You'll get

bash$ ghc -O -o foo Foo.hs
bash$ ./foo
foo: Oops!  Entered absent arg w_s4vl Int

Ugh! This is the bug underlying this bug report.

I know what is going on.

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture