GHC Proposal: Top-level IO initialized bindings

github.com/ghc-proposals/ghc-proposals

Top-level IO initialized bindings (#766)

master ← brandonchinn178:top-level-io

opened 04:46AM - 29 Jun 26 UTC

        brandonchinn178
      

+176 -0

Rendered

This has been a long-standing discussion, as documented at the Top-level mutable state page in the Haskell Wiki. After discussion in Can NOINLINE fail to prevent inlining?, this is my attempt at the problem.

The core of my proposal is:

• OPAQUE is better than NOINLINE for this idiom, but it’s not obvious that one should use OPAQUE over NOINLINE
• One must use unsafePerformIO, but it’s not actually unsafe if one uses OPAQUE. You lose ordering guarantees with regard to other IO actions, but that’s no more unsafe than hGetContents.
• foo :: %TopLevelIO (IORef Int); foo = newIORef 0 is actually semantically sound and safe, provided the compiler respect the modifier