Stability of Uniques

[Simon Peyton-Jones]

Indeed the type checker does not actually clone identifiers.

ghc -c -ddump-rn -ddump-tc -dppr-debug Foo.hs

==================== Renamer ====================
nonrec {Foo.hs:3:1-8}
       main:Foo.f{v r0}
       main:Foo.f{v r0}
         = {Foo.hs:3:5-8}
           ghc-prim:GHC.Types.True{(w) d 6u}
       <>

TYPE SIGNATURES
    ( main:Foo.f{v r0} [lid] :: ghc-prim:GHC.Types.Bool{(w) tc 3c} ) :: ghc-prim:GHC.Types.Bool{(w) tc 3c}
TYPE CONSTRUCTORS
COERCION AXIOMS
Dependent modules: []
Dependent packages: [base, ghc-prim, integer-gmp]

==================== Typechecker ====================
{Foo.hs:3:1-8}
AbsBinds
[]
[]
[( main:Foo.f{v r0} [lid] :: ghc-prim:GHC.Types.Bool{(w) tc 3c} ) <= ( f{v a9H} [lid] :: ghc-prim:GHC.Types.Bool{(w) tc 3c} )
   <>]
  ( main:Foo.f{v r0} [lid] :: ghc-prim:GHC.Types.Bool{(w) tc 3c} )
    :: ghc-prim:GHC.Types.Bool{(w) tc 3c}
  [LclId]
  {Foo.hs:3:1-8}
  ( f{v a9H} [lid] :: ghc-prim:GHC.Types.Bool{(w) tc 3c} )
    :: ghc-prim:GHC.Types.Bool{(w) tc 3c}
  [LclId]
  ( f{v a9H} [lid] :: ghc-prim:GHC.Types.Bool{(w) tc 3c} )
    = {Foo.hs:3:5-8}
      ghc-prim:GHC.Types.True{(w) v 6v}
  <>
EvBinds{}



From: Edsko de Vries [mailto:edskodevries at gmail.com]
Sent: 27 March 2013 14:04
To: Simon Peyton-Jones
Cc: ghc-devs at haskell.org
Subject: Re: Stability of Uniques

So is there any way that I can see that an identifier in the renamed AST is really the same as an identifier in the typechecked AST?

On Wed, Mar 27, 2013 at 1:57 PM, Simon Peyton-Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>> wrote:
Yes, locally-bound uniques change all the time, to maintain scoping hygiene.  But top-level things from other modules have uniques that do not change.

simon

From: ghc-devs-bounces at haskell.org<mailto:ghc-devs-bounces at haskell.org> [mailto:ghc-devs-bounces at haskell.org<mailto:ghc-devs-bounces at haskell.org>] On Behalf Of Edsko de Vries
Sent: 26 March 2013 15:05
To: ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>
Subject: Stability of Uniques

Hi all,

Consider the very simple test

  module Test2 where
  f = True

When walking the AST after renaming I see that f has unique 1912603236 and True has unique 905969694. However, when walking the typechecked AST f seems to have unique 1627390565 instead. Should I expect that the unique associated with identifiers changes between renaming and typechecking? Or is there something else that I'm missing?

Thanks!

Edsko

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