#5590: "guarded instances": instance selection can add extra parameters to the
class
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Reporter: nfrisby | Owner: simonpj
Type: feature request | Status: new
Priority: normal | Milestone: 7.6.1
Component: Compiler (Type checker) | Version: 7.2.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by nfrisby):
Yet more motivation: guarded instances would simply the approach to
"overcoming overlapping instances", as described by Oleg here. (Indeed,
that's the same context in which I thought of the feature.)
http://okmij.org/ftp/Haskell/typeEQ.html#without-over
In particular, "guarded instances" would mitigate the need for "replica
classes", such as his `ShowList'`.
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5590#comment:4>
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