Re: Fixing type synonyms to Uniq(D)FM newtypes

In a way, if these types need to exist at all, they probably should be newtypes. That being said, I'm pretty sure that the current APIs are incomplete, so turning these into newtypes may be, in fact, quite a bit of work. But if we are starting this discussion, I'd like to understand first why all these types exist at all? Why not use `UniqFM` everywhere? /Arnaud On Tue, Jan 14, 2020 at 7:16 AM Ömer Sinan Ağacan wrote:

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but I still don't quite understand the motivation

I give a concrete example (something that happened to me that I had to debug in runtime) in the issue I linked in my original post.

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For example, delVarEnv will only work with a Var, not a Name.

delVarEnv will happily accept a NameEnv in its first argument, which is the problem I was trying to describe.

Ömer

Richard Eisenberg , 14 Oca 2020 Sal, 01:55 tarihinde şunu yazdı:

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I'd be fine with making these newtypes, but I still don't quite

understand the motivation. Note that the specialized functions for the different instances of UniqFM all have type signatures. For example, delVarEnv will only work with a Var, not a Name.

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Was there a different scenario that you want to avoid?

Thanks, Richard

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On Jan 13, 2020, at 9:10 AM, Ömer Sinan Ağacan

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Hi,

UniqFM and UniqDFM types are basically maps from Uniques to other

stuff. Most of

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the time we don't actually map Uniques but instead map things like Vars or Names. For those we have types like VarEnv, NameEnv, FastStringEnv, ... which are defined as type synonyms to UniqFM or UniqDFM, and operations are defined like

extendFsEnv = addToUFM extendNameEnv = addToUFM extendVarEnv = addToUFM

This causes problems when I have multiple Uniquables in scope and use

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one to update an environment because the program type checks and does

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thing in runtime. An example is #17667 where I did

delVarEnv env name

where `name :: Name`. I shouldn't be able to remove a Name from a Var env but this currently type checks.

Two solutions proposed:

- Make these env types newtypes instead of type synonyms. - Add a phantom type parameter to UniqFM/UniqDFM.

If you could share your opinion on how to fix this I'd like to fix

wrote: the wrong the wrong this soon.

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Personally I prefer (1) because it looks simpler but I'd be happy with (2) as well.

Ömer _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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