| Yes I have a branch, and it works! A bunch of things is still missing | (notably record selectors), but I have a proof-of-concept with a gdiff | library hooked up to GHC.Generics, and by appealing to type-level | reasoning I can obtain a difference tree from True to False (which | looks good) by using the reflection (i.e. class Generic) only, no need | for TH or hand-coding. Comparing bigger trees (and then 'patch'ing | them) appears to be SMOP from here. Do you have a wiki page explaining what "it" is (the thing that works). | instance Datatype (Dat "MyModule" "Foo") ... | | I get an 'orphan instance' warning. I believe that these are harmless, The downside of orphan instances is that GHC must visit every .hi file that has an orphan instance, just in case it contains a relevant instance decl. That slows down *every* compilation, whether or not it uses the instance. The best way to get rid of it is to declare something local that is "from this module". Something like data MyModule_Foo instance DataType (Dat MyModule_Foo) where ... Now MyModule_Foo is a data type from the module currently being compiled. That tells GHC which .hi file to look in, and means the instance isn't orphan. Simon | so is there a way to suppress them? Since I never insert tyvars in the | instance head, there should never be any overlap too. | | Cheers, | | Gabor | | On 6/30/14, Simon Peyton Jones wrote: | > You'll need to give a lot more info than this before I can help Gabor. | > Currently I have only the vaguest idea about what you are trying to | > accomplish. Is there a wiki page that describes the design (user's eye | > view) in detail? | > | > I see you have a branch. If you are stuck, and give me repro | instructions, | > I can attempt to help. | > | > Simon | > | > | -----Original Message----- | > | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of | Gabor | > | Greif | > | Sent: 27 June 2014 17:51 | > | To: ghc-devs | > | Subject: Resolved+new Q: TypeLits question, how to build a Type | > | Application with Symbol index | > | | > | I succeeded to solve all of them :-) | > | | > | But now I am blocked on on a panic | > | | > | "not in scope during type checking, but it passed the renamer". | > | | > | I suspect that while "deriving Generic" some instances are defined in | > | some empty TcEnv, which does not contain my definition in context. | > | | > | Is there a way to inject some type constructor into the TcEnv? | > | | > | Thanks, | > | | > | Gabor | > | | > | On 6/27/14, Gabor Greif wrote: | > | > Hello devs, | > | > | > | > I have | > | > | > | > {{{ | > | > data D (n :: Symbol) | > | > }}} | > | > | > | > in my module, and I want to obtain a type | > | > | > | > {{{ | > | > D "YAY!" | > | > }}} | > | > | > | > programmatically. Where can I find code that performs this (or | > | > something similar)? | > | > | > | > 1) I have to look up |D| in the current TyEnv (what if it is in a | > | > specific module?), | > | > 2) I have to build the type index (of kind Symbol), this involves | > | > FastString, looks non-trivial, | > | > 3) Apply 1) on 2), this is easy. | > | > | > | > Any hints welcome! | > | > | > | > Thanks and cheers, | > | > | > | > Gabor | > | > | > | > | > | > PS: some morsels I have so far: | > | > | > | > for 1) | > | > compiler/prelude/PrelNames.lhs:gHC_GENERICS = mkBaseModule | (fsLit | > | > "GHC.Generics") | > | > | > | _______________________________________________ | > | ghc-devs mailing list | > | ghc-devs@haskell.org | > | http://www.haskell.org/mailman/listinfo/ghc-devs | >