Ganesh Sittampalam wrote:
If you want to standardise a language feature, you have to explain its
behaviour properly. This is one part of the necessary explanation.
To be concrete about scenarios I was considering, what happens if:
- the same process loads two copies of the GHC RTS as part of two
completely independent libraries? For added complications, imagine that
one of the libraries uses a different implementation instead (e.g. Hugs)
- one Haskell program loads several different plugins in a way that
allows Haskell values to pass across the plugin boundary
How do these scenarios work with use cases for <- like (a) Data.Unique
and (b) preventing multiple instantiation of a sub-library?
That's a good question. But before you propose these scenarios, you must
establish that they are sane for Haskell as it is today.
In particular, would _local_ IORefs work correctly? After all, the
memory allocator must be "global" in some sense. Could you be sure that
different calls to newIORef returned separate IORefs?
Perhaps this is the One True Global Scope: the scope in which refs from
newIORef are guaranteed to be separate. It's the scope in which values
from newUnique are supposed to be different, and it would also be the
scope in which top-level <- would be called at most once.
--
Ashley Yakeley
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