Template Haskell stability

[Teofil Camarasu]

There's been a bit of discussion about template haskell stability on this
issue that you might find interesting:
https://gitlab.haskell.org/ghc/ghc/-/issues/24021

Cheers,
Teo

On Sun, Mar 10, 2024 at 5:11 PM Iavor Diatchki <iavor.diatchki at gmail.com>
wrote:

> 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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