Alright, I opened an issue, https://gitlab.haskell.org/ghc/ghc/-/issues/20641, and I'll make an MR later.
Any objections if I change the implementation of GHC.Core.Utils.eqExpr :: InScopeSet -> Expr -> Expr -> Bool https://gitlab.haskell.org/ghc/ghc/-/blob/master/compiler/GHC/Core/Utils.hs#L2124 to eqExpr _ e1 e2 = deBruijnize e1 == deBruijnize e2 and at the same time mark it deprecated telling people to use deBruijnize? (I don't want to remove it since GHC API users might be using it) `eqExpr` also does alpha-equivalence on CoreExpr, and has the same mistake w.r.t. alpha-equivalence as the `Eq (DeBruijn CoreExpr)` instance -- Christiaan On Mon, 8 Nov 2021 at 13:02, Simon Peyton Jones <simo...@microsoft.com> wrote: > Huh! Dead right! > > > > Would you like to: > > - Open a ticket (you can use the text from this email) > - Submit a MR? > > > > On the MR, > > - Add a Note that again gives your killer example; and mention why we > don’t need the check for NonRec > - Worth also pointing out that letrec { x = e1; y = e2 } in b is NOT > considered equal to letrec { y = e1; x = e1 } in b. Nor are let x=e1 in > let y = e2 in b considered equal to let y = e1 in let x = e1 in b. > This is fine; but worth pointing out. > > > > Thanks for pointing this out! > > > > Simon > > > > PS: I am leaving Microsoft at the end of November 2021, at which point > simo...@microsoft.com will cease to work. Use simon.peytonjo...@gmail.com > instead. (For now, it just forwards to simo...@microsoft.com.) > > > > *From:* ghc-devs <ghc-devs-boun...@haskell.org> *On Behalf Of *Christiaan > Baaij > *Sent:* 07 November 2021 21:08 > *To:* ghc-devs <ghc-devs@haskell.org> > *Subject:* Alpha-equivalence for recursive let-bindings > > > > Hi list, > > > > I was looking at the `Eq (DeBruijn CoreExpr)` instance and I noticed that > the types of recursive let-bindings aren't checked for alpha-equivalence: > > > > > https://gitlab.haskell.org/ghc/ghc/-/blob/master/compiler/GHC/Core/Map/Expr.hs#L166-174 > <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fblob%2Fmaster%2Fcompiler%2FGHC%2FCore%2FMap%2FExpr.hs%23L166-174&data=04%7C01%7Csimonpj%40microsoft.com%7C4e4f1afdc4d64d66f2ef08d9a232bca8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637719161836942634%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=6TGl3MHDSGLyUFjfMwce13K%2FVprCl7YRMQnRGrJj%2BAI%3D&reserved=0> > > > > go (Let (Rec ps1) e1) (Let (Rec ps2) e2) > = equalLength ps1 ps2 > && D env1' rs1 == D env2' rs2 > && D env1' e1 == D env2' e2 > where > (bs1,rs1) = unzip ps1 > (bs2,rs2) = unzip ps2 > env1' = extendCMEs env1 bs1 > env2' = extendCMEs env2 bs2 > > > > But doesn't that mean that: > > let (x :: Int) = x in x > > and > > let (y :: Bool) = y in y > > are considered alpha-equivalent? > > If that is the case, then I think that's wrong. Agree? > > I understand that you don't have to check types for non-recursive > let-bindings: when the RHSs match, the types must be the same. > > > > -- Christiaan > > >
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