<div dir="ltr"><div class="gmail_default" style="font-family:tahoma,sans-serif">A `ModDetails` gives the type signatures for everything, but no actual code. For example if you have `f :: Int -> Int` in the `md_types`, the `ModDetails` doesn't include the binding `f = rhs` for `f`.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">Presumably you must also be generating these bindings (in a `ModGuts` perhaps?) and generating code for them that will ultimately be linked into the program to run.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">Well, put the `DFunId` binding in the same place, alongside `f`.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">Does that help?</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">Simon<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 10 Feb 2022 at 09:49, Erdi, Gergo via ghc-devs <<a href="mailto:ghc-devs@haskell.org">ghc-devs@haskell.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">Hi,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">I’m trying to make a module out of thin air and register it to GHC so that other modules can import it. So far, I have had success with making a ModIface and a ModDetails, and
then registering them using the following function:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console"">registerModule :: (GhcMonad m) => ModIface -> ModDetails -> m ()<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console"">registerModule iface details = modifySession $ extendHpt . addModule<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> where<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> mod_info = HomeModInfo iface details Nothing<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> mod = mi_module iface<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> modOrig = ModOrigin (Just True) [] [] True<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> addModule = modifyUnitState $ \us -> us<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> { moduleNameProvidersMap = M.insert (moduleName mod) (M.singleton mod modOrig) $ moduleNameProvidersMap us<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> }<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> extendHpt env = env<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> { hsc_unit_env = let ue = hsc_unit_env env in ue<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> { ue_hpt = hpt<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> }<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> }<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> where<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> hpt = addToHpt (hsc_HPT env) (moduleName mod) mod_info<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">This worked when I was only _<i>declaring</i>_ functions and TyCons in these modules. However, now I would also like to add instances. And I’m hitting a problem here, because
I don’t know where to put the actual definitions of the instance. I’m completely lost here.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">Here’s what I’m doing in detail. First, I make a fresh DFunId from a fresh Unique:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> let tag = occNameString . getDFunTyKey $ ty<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> occ = mkDFunOcc (occNameString (getOccName showClass) <> tag) False emptyOccSet<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> name = mkExternalName uniq mod occ loc<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> dfun = mkDictFunId name [] [] showClass [ty]<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">Then, I make a ClsInst that describes my instance:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> return ClsInst<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> { is_cls_nm = getName showClass<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> , is_tcs = [KnownTc $ getName tycon]<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> , is_dfun_name = getName dfun<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> , is_tvs = []<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> , is_cls = showClass<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> , is_tys = [ty]<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> , is_dfun = dfun<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> , is_flag = OverlapFlag (NoOverlap NoSourceText) False<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> , is_orphan = NotOrphan (getOccName $ getName tycon)<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> }<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">And then I add ‘AnId dfun’ to my ModDetails’s type env in ‘md_types’,, add the instance to the ‘md_insts’, and fill the ‘mi_decls’ and ‘mi_insts’ of the ModIface accordingly.
This gives me a ModIface/ModDetails pair just like before – but I never said what the definition of ‘dfun’ is!
<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">When I try compiling a real source module that imports this synthetic module and tries to use the instance, it gets as far as the “Desugar (after optimization)” step, and then
fails with:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console"">ghc-mu-core-to-exp: panic! (the 'impossible' happened)<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> GHC version 9.3.20211130:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> lookupIdSubst<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console"">$fShowOrderPolicy<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console"">InScope {foo mapM_}<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console"">Call stack:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> CallStack (from HasCallStack):<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> callStackDoc, called at compiler/GHC/Utils/Panic.hs:181:37 in ghc-lib-0.20211130-7QA7vLTw0OYJmMsraoHe3v:GHC.Utils.Panic<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""> pprPanic, called at compiler/GHC/Core/Subst.hs:260:17 in ghc-lib-0.20211130-7QA7vLTw0OYJmMsraoHe3v:GHC.Core.Subst<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Console""><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">I’m not surprised that eventually it crashes and burns, because, again, I have only declared my DFunId (‘$fShowOrderPolicy’ in this case), but never defined it. Its definition
would be a CoreExpr, right? So where would I put the pair of ‘(dfun, myCoreExprOfTheRightType)’ for GHC to pick it up? Or is it the case that GHC would only need an ‘Id’s definition if it is trying to inline/specialize it, i.e. should I just attach the definition
to the DFunId as an unfolding? Or is ‘registerModule’ already incomplete and it should put the ‘CoreProgram’ of the module to somewhere deep in the GHC state?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif">Thanks,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10pt;font-family:"Arial",sans-serif"> Gergo<u></u><u></u></span></p>
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