Chad Scherrer wrote:
> x = runST $ return 1
>
> y = runST $ do {r <- newSTRef 1; readSTRef r}
>
> Neither of these works in ghci
x = runST (return 1)
y = runST (do {r <- newSTRef 1; readSTRef r})
The escaping s is something to do with rank 2 polymorphism.
(Search for "rank" in the ghc user guide, for example.)
The hassle is that runST must always be applied to an
argument (e.g. not passed to ($)), and a benefit is that
you're protected from using an STRef you created in the
context of one runST, in the context of another runST.
Regards,
Tom
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