[Haskell-cafe] inference with implicitparams seems broken

rowan goemans goemansrowan at gmail.com
Thu Mar 24 21:37:30 UTC 2022

Hi Richard,

Thanks for answering. I have made a tiny change to GHC in a fork that 
lifts the monomorphization restriction but only for implicit params. See 
this commit: 

Is there some example I could run to see in action why the 
monomorphisation restriction is required? I looked at the Haskell report 
and I don't immediately see why the points raised apply to implicit 
params. I get a feeling that monomorph(Contains only a concrete type 
like Int or Bool) implicit params would never be a problem and maybe 
only polymorphic ones are?

Rowan Goemans

On 3/24/22 20:05, Richard Eisenberg wrote:
>> On Mar 24, 2022, at 9:04 AM, rowan goemans <goemansrowan at gmail.com> 
>> wrote:
>> is this by design/expected though?
> It is by design, yes. With a sufficiently nuanced expectation, I would 
> also say it's expected. (Though, to be fair, if I were not primed to 
> be thinking about the monomorphism restriction, I can't honestly say I 
> would get it right if quizzed.)
>> Would there be interest in fixing this in GHC?
> Figuring out when to generalize a local binding is a hard problem. So, 
> there is definitely interest in finding a better way to do it, but I 
> don't think anyone knows a design that meets the most expectations. 
> Language design is hard! :)
> Richard
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