#3547: Improve granularity of UndecidableInstances
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Reporter: ksf | Owner:
Type: feature request | Status: new
Priority: normal | Component: Compiler
Version: 6.10.4 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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Currently, as a LANGUAGE pragma, UndecidableInstances can only be set once
per file: Assuming that there are enough occasions where one would only
need to enable it for one or two instances in a bigger source and
considering that the warnings emitted if UndecidableInstances is not set
are actually useful, it makes sense to support enabling the extension only
on a per-instance basis.
proposed syntax:
{{{
{-# LANGUAGE UndecidableInstances #-}
[code]
{-# NOLANGUAGE UndecidableInstances #-}
}}}
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3547>
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