Er, dictionary... sorry, mkDataOccFS On Tue, Mar 22, 2016 at 5:24 PM, Andrew Farmer wrote:

mkVarUnqual calls mkVarOccFS, which constructs an OccName in the varName namespace. You need to construct your RdrName via mkTyVarOcc, which picks the Type/Class namespace.

On Tue, Mar 22, 2016 at 5:09 PM, Conal Elliott wrote:

...

I'm trying to construct a dictionary in a GHC plugin. I'm stuck on finding the constructor for the dictionary. When I use `-ddump-simpl` on the module that defines the class, I see "Circat.Rep.C:HasRep". To try finding that constructor, I say

...

lookupRdrNameInModuleForPlugins hsc_env (mkModuleName "Circat.Rep") (mkVarUnqual "C:HasRep")

However, I keep getting `Nothing` as a result. (Same without the "C:".) I've also had this same difficulty when looking up constructors for algebraic data types and when looking up TyCons. For regular value Ids, lookup succeeds.

What am I missing?

Thanks, - Conal

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I'm now able to look up value identifiers, type constructors (including classes), and regular data constructors, but not dictionary constructors. Here's my failing effort to look up a dictionary constructor (in CoreM): hasRepThing <- maybe (panic "HasRep lookup failure") lookupThing =<< (liftIO $ lookupRdrNameInModuleForPlugins hsc_env (mkModuleName "Circat.Rep") (Unqual (mkDataOcc "C:HasRep"))) pprTrace "mkReifyEnv HasRep thing:" (ppr hasRepThing) (return ()) Result: ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.1.20160307 for x86_64-apple-darwin): HasRep lookup failure Same failure when I use the name string "HasRep" in place of "C:HasRep". Any idea what I'm doing wrong here? -- Conal On Tue, Mar 22, 2016 at 5:40 PM, Conal Elliott wrote:

Got it. Silly me. Thanks!! - Conal

On Tue, Mar 22, 2016 at 5:25 PM, Andrew Farmer wrote:

...

Er, dictionary... sorry, mkDataOccFS

...

mkVarUnqual calls mkVarOccFS, which constructs an OccName in the varName namespace. You need to construct your RdrName via mkTyVarOcc, which picks the Type/Class namespace.

On Tue, Mar 22, 2016 at 5:09 PM, Conal Elliott wrote:

...

I'm trying to construct a dictionary in a GHC plugin. I'm stuck on finding the constructor for the dictionary. When I use `-ddump-simpl` on the module that defines the class, I see "Circat.Rep.C:HasRep". To try finding

On Tue, Mar 22, 2016 at 5:24 PM, Andrew Farmer wrote: that

...

...

constructor, I say

...

lookupRdrNameInModuleForPlugins hsc_env (mkModuleName "Circat.Rep") (mkVarUnqual "C:HasRep")

However, I keep getting `Nothing` as a result. (Same without the "C:".) I've also had this same difficulty when looking up constructors for algebraic data types and when looking up TyCons. For regular value Ids, lookup succeeds.

What am I missing?

Thanks, - Conal

_______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

Indeed, tyConDataCons does the trick. I don't know how to start with the Class (given a name string), but I'm able to use 'mkClsOcc . Unqual' with lookupRdrNameInModuleForPlugins and then lookupTyCon on the resulting name, followed by 'head . tyConDataCons' to get the constructor. Thanks, Simon! -- Conal On Wed, Mar 23, 2016 at 1:32 AM, Simon Peyton Jones wrote:

Start with the Class. Use classTyCon to get the TyCon. Use tyConDataCons to get the data constructor.

Simon

*From:* ghc-devs [mailto:ghc-devs-bounces@haskell.org] *On Behalf Of *Conal Elliott *Sent:* 23 March 2016 00:09 *To:* ghc-devs@haskell.org *Subject:* lookupRdrNameInModuleForPlugins with constructors

I'm trying to construct a dictionary in a GHC plugin. I'm stuck on finding the constructor for the dictionary. When I use `-ddump-simpl` on the module that defines the class, I see "Circat.Rep.C:HasRep". To try finding that constructor, I say

...

lookupRdrNameInModuleForPlugins hsc_env (mkModuleName "Circat.Rep") (mkVarUnqual "C:HasRep")

However, I keep getting `Nothing` as a result. (Same without the "C:".) I've also had this same difficulty when looking up constructors for algebraic data types and when looking up TyCons. For regular value Ids, lookup succeeds.

What am I missing?

Thanks, - Conal