Optimisation removes effectful computation.
Summary
The attached zip contains a small cabal package with a Win32 dependency.
The problematic source file in question is Offending.hs, where the optimisation level was overridden.
Steps to reproduce
When setting the optimisation level in Offending.hs to -O1, and doing a full rebuild
(running cabal clean if neccessary), the resulting program prints the following:
Sending mask: 0Somehow, the second call to sendMessage in Offending.hs gets dropped.
Expected behavior
When setting the optimisation level in Offending.hs to -O0, the program prints the expected result:
Sending mask: 0
Recieved new mask: 2Environment
- GHC version used: 8.10.1