On 12 April 2016 at 07:36, Matthias Fischmann wrote:

On Tue, Apr 12, 2016 at 02:22:23PM +1000, Erik de Castro Lopo wrote:

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Date: Tue, 12 Apr 2016 14:22:23 +1000 From: Erik de Castro Lopo To: ghc-devs@haskell.org Subject: TH changes for ghc 8.0

Hi all,

I'm working on updating persistent-template for ghc-8.0 and reading the migration guide:

https://ghc.haskell.org/trac/ghc/wiki/Migration/8.0#template-haskell-2.11.0....

specifically the bit that says:

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* the DataD, NewtypeD, DataInstD, and NewtypeInstD constructors have a new field `Maybe Kind` (#10828), and take a `CxtQ` instead of a `[Name]` for the derived classes (#10819). If you don't know what to do, use `Nothing` for the kind signature, and `cxt []` for the derived classes.

Using `Nothing` as suggested is working out well enough, but I'm a bit befuddled by the change from `[Name]` to `CtxQ` and the usage of `ctx []`. I can't seem to find *any* function named `ctx`.

the docs say `cxt`, not `ctx`.

not sure what that means either. (-:

That function does exist for me in rc2: cxt :: [PredQ] -> CxtQ Erik

mapM conT :: [Name] -> Q [Type] :: [Name] -> Q [Pred] :: [Name] -> CxtQ Those `Name`s are Class names, which are Type constructors, hence `conT` Christiaan On 04/12/2016 10:17 AM, Erik de Castro Lopo wrote:

Erik Hesselink wrote:

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That function does exist for me in rc2:

cxt :: [PredQ] -> CxtQ

Ah, there is it is!

But I'm trying to write code that works with ghc-7.10 *and* ghc-8.0 (yes, I'm using CPP in all its ugly glory), but if I've got code that works with ghc-7.10 (the first type signature below):

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- dataD :: CxtQ -> Name -> [TyVarBndr] -> [ConQ] -> [Name] -> DecQ + dataD :: CxtQ -> Name -> [TyVarBndr] -> Maybe Kind -> [ConQ] -> CxtQ -> DecQ

how do I convert it to the second? Adding a `Nothing` for the `Maybe Kind` argument is easy, but if the old code has `[Name]`, how do I convert it to a `CxtQ`. The `cxt` function won't do it.

Erik

Erik de Castro Lopo writes:

Christiaan Baaij wrote:

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mapM conT :: [Name] -> Q [Type] :: [Name] -> Q [Pred] :: [Name] -> CxtQ

Those `Name`s are Class names, which are Type constructors, hence `conT`

Thanks Christiaan, thats got it for me. I'll update the migration guide as well.

Thanks Erik! Cheers, - Ben