#3928: Turn SampleVar into an abstract newtype
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Reporter: basvandijk | Owner:
Type: proposal | Status: new
Priority: normal | Component: libraries/base
Version: 6.12.1 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
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a {{{Control.Concurrent.SampleVar}}} is currently a type synonym:
{{{type SampleVar a = MVar (Int, MVar a)}}}
This has two problems:
* Users can "screw up" the internal state.
* We can't define instances for {{{SampleVars}}} without using the
{{{TypeSynonymInstances}}} language extension.
My proposal is to turn {{{SampleVar}}} into an abstract newtype like:
{{{newtype SampleVar a = SampleVar (MVar (Int, MVar a))}}}
The related discussion on {{{[email protected]}}} contains the patch
that implements this:
http://thread.gmane.org/gmane.comp.lang.haskell.libraries/12626
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3928>
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