#14664: "GHC.Integer can't throw exceptions" is wrong -------------------------------------+------------------------------------- Reporter: Zemyla | Owner: (none) Type: feature | Status: new request | Priority: low | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The various integer packages, and anything else that might be loaded before the Prelude, goes through contortions to report errors, or else doesn't report them and crashes, because those packages are compiled before the `Exception` type is available. However, there is a way to throw exceptions from code that only has access to `ghc-prim`. It relies on the fact that the RTS itself throws an exception in a certain circumstance: when `atomically` is called from within `atomically`. This gives us the following: {{{#!hs {-# LANGUAGE MagicHash, UnboxedTuples, NoImplicitPrelude #-} import GHC.Prim import GHC.Magic atomicLoop :: State# RealWorld -> (# State# RealWorld, a #) atomicLoop s = atomically atomicLoop s exception :: a exception = runRW# (\s -> case atomicLoop s of (# _, a #) -> a) }}} I think that `integer-simple` and `integer-gmp`, and maybe the very earliest parts of `base`, are the only packages that would benefit from this circumlocution; however, having the error be a catchable exception rather than a straight-up crash has benefits. Priority is low because I don't think there have been any bugs regarding GHC.Integer crashing; I just think it might make the code a bit more elegant. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14664 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler