On 13 October 2004 16:17, Wolfgang Thaller wrote:
> We could get away with "desugaring" them to some very "unsafe" non-IO-
> bindings and having the "module init action" do something evil to
> make the IO happen in the right order... should be possible to make
> that look exactly like mdo from the outside.
> We'll end up using the unsafePerformIO hack inside the implementation
> again, so that people end up with two IORefs instead of one, but that
> should be cheap enough:
>
> foo <- someAction
>
> ... could be transformed into ...
>
> foo_var = unsafePerformIO $ newIORef (throw NonTermination)
> foo_action = someAction >>= writeIORef foo_var
> foo = unsafePerformIO $ readIORef foo
>
> ... with the appropriate NOINLINEs.
> The module init action would then make sure that foo_action gets
> invoked.
Yes, we could do that. The fact that we're using NOCSE/NOINLINE
internally still seems very fragile, though. Oh well, perhaps we have
to live with that if we don't want the pain of a special binding type
throughout the compiler.
Cheers,
Simon
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