#836: rebindable if-then-else syntax
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Reporter: nibro | Owner: SamAnklesaria
Type: feature request | Status: new
Priority: normal | Milestone: _|_
Component: Compiler (Parser) | Version: 6.13
Keywords: | Testcase: N/A
Blockedby: | Difficulty: Unknown
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by simonpj):
My thoughts
* Like igloo, I would much prefer a `RebindableSyntax` flag (using
`ImplicitPrelude` is anyway a hack) than one for 'if' alone. I really
don't want `RebindableIf`.
* There is no difficulty with using the old typing rule for `if` when
`RebindableSyntax` is off, and the new one when it is on. (That isn't the
way other rebindable syntax is done, but it doesn't matter.) Doing that
means that the Prelude doesn't need to export `ifThenElse`
* Many libraries use if, but few (none?) use both (a) rebindable syntax
and (b) `if` with an unlifted return type. That would be the unsupported
combination under the new scheme. But there's a way out in that case: use
`case`.
In short, my proposal is:
* Add `RebindableSyntax` flag. (It might imply `NoImplicitPrelude`.)
* Choose which typing rule to use for `if` based on the flag
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/836#comment:28>
GHC <http://www.haskell.org/ghc/>
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