ExprWithTySigOut

[Herbert Valerio Riedel]

Hi,

Btw, I also used that annoying pattern in

  https://phabricator.haskell.org/D1185

to represent type-signature sections before/after typechecking:
  
​  -- | Type-signature operator sections
​
​  | TySigSection    (LHsType id)
​		    (PostRn id [Name])	-- wildcards
​
​  | TySigSectionOut (LHsType Name)
​		    (PostTc id Type)
​		    (PostTc id Coercion)

I'd be interested in better ideas as well...

On 2015-12-21 at 09:46:58 +0100, Simon Peyton Jones wrote:
> Yes this is annoying.
>
> The thing is that with the first constructor only we'd get
> 	(LHsSigWcType Id)
> after type checking, but we don't have such a thing. `HsTypes` are typechecked to `Types`.  
>
> Perhaps we could have
> 	(LHsSigWcType (StopAtRenamer d))
>
> where
> 	type family StopAtRenamer a where
> 		StopAtRenamer Id = Name
> 		StopAtRenamer x = x
>
> If this pattern happened a lot it might be worth it.  But I think this is the only occurrence.
>
> Better ideas welcome.
>
> Simon
>
> |  -----Original Message-----
> |  From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Alan
> |  & Kim Zimmerman
> |  Sent: 19 December 2015 13:15
> |  To: ghc-devs at haskell.org
> |  Subject: ExprWithTySigOut
> |  
> |  At the moment HsExpr includes the following two constructors
> |  
> |    | ExprWithTySig
> |                  (LHsExpr id)
> |                  (LHsSigWcType id)
> |  
> |    | ExprWithTySigOut              -- Post typechecking
> |                  (LHsExpr id)
> |                  (LHsSigWcType Name)  -- Retain the signature,
> |                                       -- as HsSigType Name, for
> |                                       -- round-tripping purposes
> |  
> |  I do not understand why we need the second one, which hard-codes Name
> |  instead of id.
> |  
> |  There are a couple of places where there is an XXXOut variant with
> |  hard coded Name parameter, and these complicate creating any kind of
> |  custom class intended to work on a parameterised AST as it ripples out
> |  and forces Name instances of it everywhere.
> |  
> |  Perhaps we should introduce HsExprLR id id to cope with renaming?
> |  
> |  Alan
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