Template Haskell stability

[Iavor Diatchki]

Oh, that's really confusing, especially since the internal one is what
shows up first when you search for stuff!

Another example of similar breakage was the changes to binders a little
while ago.

On Sun, Mar 10, 2024 at 10:02 AM Oleg Grenrus <oleg.grenrus at iki.fi> wrote:

>  > So what do I do?
>
> There are two tupE functions.
>
> In Language.Haskell.TH.Lib.Internal module the type has changed. That's
> the module used by GHC itself, to represent quotations. As the module
> documentation says
>
>  > Language.Haskell.TH.Lib.Internal exposes some additional
> functionality that is used internally in GHC's integration with Template
> Haskell. This is not a part of the public API, and as such, there are no
> API guarantees for this module from version to version.
>
> In the Language.Haskell.TH.Lib module which is documented as
>
>  > Language.Haskell.TH.Lib contains lots of useful helper functions for
> generating and manipulating Template Haskell terms
>
> the type of tupE [1] has been left unchanged, and it's still
>
>     tupE :: Quote m => [m Exp] -> m Exp
>
> [1]
>
> https://hackage.haskell.org/package/template-haskell-2.21.0.0/docs/Language-Haskell-TH-Lib.html#v:tupE
>
> ---
>
> Oleg
>
>
> On 10.3.2024 18.56, Iavor Diatchki wrote:
> > Hello,
> >
> > I am not sure if this is the right list to post to, but I suspect
> > template-haskell is mostly modified by GHC folk, which is why I chose
> > to post here, and there is no maintainer listed, based just the
> > `libraries` list.
> >
> > Template Haskell is a very useful tool, but I am always quite wary of
> > using it, because it is so unstable.   I understand the need to change
> > the syntax, as the language evolves, but I feel that changes are made
> > without any consideration for backward compatibility, which is very
> > unfortunate.
> >
> > To give you an example, I am currently using GHC 9.6.4, and I am
> > working on a small TH utility.  I need to make a tuple expression, but
> > of a dynamic size, so I can't use the special syntax, and need to use
> > a function to do so.  So I am using the function, `tupE`, which has
> > the following type:
> >
> >     tupE :: Quote m => [m Exp] -> m Exp
> >
> > This is quite nice and unsurprising.   When I look oh `hackage`,
> > however, the type of this function has changed, now it is:
> >
> >    tupE :: Quote m => [m (Maybe Exp)] -> m Expr
> >
> > So what do I do?  Basically I should not use this function, because as
> > soon as I upgrade the compiler everything will break!  Furthermore
> > there is no documentation at all to explain what this function is
> > supposed to do (I can't fathom why it is taking `Maybe` as arguments),
> > or when it changed, etc.
> >
> > So my plea would be---change the syntax at will, but let's try to keep
> > the convenience functions that build the syntax stable: instead of
> > changing functions, it is just as easy to add a new function.  I
> > understand that sometimes things need to change, but then we should
> > describe what changed, and in which versions.   I don't think these
> > are hard things to do, and I really think it will have great benefit
> > to everyone using TH.
> >
> > Cheers,
> > -Iavor
> >
> >
> >
> >
> >
> >
> >
> >
> > _______________________________________________
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> > ghc-devs at haskell.org
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
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