#5073: Add blockST for nested ST scopes
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.0.3
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by matthew.fluet):
It does seem simple enough to add. And I think it is a good building
block (pun?) for other, more sophisticated scope handling mechanisms,
along the lines that John alluded to.
However, it does seem that it is more useful to move *computations* from
one `ST` scope to another. That is, as mentioned in the Region Monad
paper
by way of Simon, making the two primitives be:
{{{
blockST :: (forall r. ST (s,r) a) -> ST s a
importST :: ST s a -> ST (s, r) a
}}}
`importVar` requires that you have your hands on all of the `STRef`-s,
which
makes it hard to abstract over computations. `importST` seems to simply
be
the public face of the proposed `promoteState#` primitive. (Is there a
typo in the type of `promoteState#`? The final `a` seems out of place.)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5073#comment:4>
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