Adding type signature changes semantics (was [Haskell-cafe] Lazy in either argument?)

Simon Peyton-Jones simonpj at
Fri Aug 3 03:47:24 EDT 2007

Stefan is right here.

- It's not surprising that with -Onot you get different code from different source programs, even if one can readily be transformed into the other.  That's what -O does.

| If anything I think it's a bug in the code generator/the runtime.  We
| shouldn't be generating uninterruptable loops!
| Option 1: Don't generate non-allocating loops.
| Option 2: Preempt non-allocating loops.

I would urge caution on (2).  It's an absolute swamp, especially when you want to be portable across platforms, into which many have ventured but few have re-emerged.   Those that have usually do so by adopting some variation on Option 1.

However you can do (1) without allocating: you just need to insert a test into the loop that tests the "please yield" flag, which is set by the interrupt.  The  key thing is that the thread yields voluntarily and tidily rather than being forcibly pre-empted.


More information about the Glasgow-haskell-users mailing list