Strictness/demand info for a Name

Sebastian Graf sgraf1337 at
Thu Jan 13 15:50:01 UTC 2022

Yes, every imported identifier from a module that was compiled with 
optimisations should have the proper analysis information in its IdInfo.
So if you have `base` somewhere in one of your compiled libraries and 
load it, then the identifier of `` will have an 
`idDmdSig` that says it's strict in the list parameter.

At least that's how it works in GHC, where these IdInfos are populated 
with the information from the loaded interface files. The situation with 
HLS might be different, although I wouldn't expect that.

------ Originalnachricht ------
Von: "Alejandro Serrano Mena" <trupill at>
An: "Sebastian Graf" <sgraf1337 at>
Cc: "GHC developers" <ghc-devs at>; "Matthew Pickering" 
<matthewtpickering at>
Gesendet: 13.01.2022 16:43:50
Betreff: Re: Re[2]: Strictness/demand info for a Name

>Thanks for the pointers! :)
>Knowing this, let me maybe rephrase my question: is it possible to get 
>demand information of identifiers without running the analysis itself?
>El 13 ene 2022 15:45:29, Sebastian Graf <sgraf1337 at> escribió:
>>Yes, Matt is right.
>>`dmdSigInfo` describes the how a function Id uses its arguments and 
>>variables, whereas
>>`demandInfo` describes how a (local, mostly) Id is used.
>>Note that if you wanted to go beyond type-checking, you could probably
>>run the analysis on the desugaring of the current module quite easily.
>>But the results would be misleading, as prior optimisations (that you
>>probably don't want to run) may arrange the program in a way that 
>>analysis has an easier time.
>>------ Originalnachricht ------
>>Von: "Matthew Pickering" <matthewtpickering at>
>>An: "Alejandro Serrano Mena" <trupill at>
>>Cc: "GHC developers" <ghc-devs at>
>>Gesendet: 13.01.2022 15:38:29
>>Betreff: Re: Strictness/demand info for a Name
>>>You look at `dmdSigInfo` in `IdInfo`.
>>>On Thu, Jan 13, 2022 at 2:20 PM Alejandro Serrano Mena
>>><trupill at> wrote:
>>> >
>>> >  Dear all,
>>> >
>>> >  I’m trying to bring the information about demand and strictness to 
>>>the Haskell Language Server, but I cannot find a way to do so. I was 
>>>wondering whether you could help me :)
>>> >
>>> >  Here’s my understanding; please correct me if I’m wrong:
>>> >
>>> >  The analysis runs on Core, so getting this information for the 
>>>current file would require to run the compiler further than type 
>>>checking, which is quite expensive,
>>> >  However, this analysis should somehow use known information about 
>>>imported functions, which should be readily available somewhere,
>>> >  If the above is true, what is the simplest way to get the 
>>>information for imported things? As I mentioned above, I would prefer 
>>>not to run the compiler further than the type checking phase, since 
>>>otherwise it gets too expensive for IDE usage. Right now HLS uses the 
>>>information from the .hie files.
>>> >
>>> >
>>> >  In fact, this goes into the more general question of how to show 
>>>information from different analyses within the IDE; I guess solving 
>>>the case for strictness/analysis may open the door to more (maybe 
>>>everything recorded inside a `Id`?)
>>> >
>>> >  Regards,
>>> >  Alejandro
>>> >  _______________________________________________
>>> >  ghc-devs mailing list
>>> >ghc-devs at
>>> >
>>>ghc-devs mailing list
>>>ghc-devs at
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