[GHC] #11824: GHC error in desugarer lookup

[Simon Peyton Jones]

Oh, you are right.  I was thinking of generating the Typeable bindings (and record selectors) at the end of tcTyAndClassDecls.   That would work perfectly EXCEPT that we only want to generate the module-name bindings once.

But it's easy to spot if it's been done already because tcg_tr_module is a Just.

So, I suggest you generate Typeable binding along with record selectors, at the end of tcTyAndClassDecls; but take care that mkModIdBindings is a no-op if tcg_tr_module says it's been done already.  


But I don't mind if you want to leave it as-is, provided you comment to avoid the confusion I fell into.

Simon

|  -----Original Message-----
|  From: Ben Gamari [mailto:ben at well-typed.com]
|  Sent: 17 April 2016 10:44
|  To: Simon Peyton Jones <simonpj at microsoft.com>
|  Cc: GHC developers <ghc-devs at haskell.org>
|  Subject: RE: [GHC] #11824: GHC error in desugarer lookup
|  
|  Simon Peyton Jones <simonpj at microsoft.com> writes:
|  
|  > | The problem is this: we must generate and typecheck record
|  selectors
|  > | on a per-group basis, since they may be used by later groups.
|  >
|  > Why?  Record selectors are value bindings which aren't used when
|  typechecking data types.
|  >
|  Yes, they are value bindings and may be used in bindings in later
|  groups. For instance, let's consider the following,
|  
|      data ARecord = ARecord { aField :: Int }
|  
|      $(return [])   -- group delimiter
|  
|      aFieldIncr :: ARecord -> Int
|      aFieldIncr = succ . aField
|  
|  My point in,
|  
|  > | we must generate and typecheck record selectors on a per-group
|  basis
|  
|  is that we must generate the `aField` binding before proceeding to
|  typecheck the second group (containing `aFieldIncr`). Failing to do
|  this would result in `aField` being out of scope when we attempted to
|  typecheck the RHS of `aFieldIncr`. Perhaps I have misunderstood?
|  
|  Cheers,
|  
|  - Ben