Template Haskell stability

[Oleg Grenrus]

 > 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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>
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