[Haskell-cafe] Resources on how to implement (Haskell 98) kind-checking?

Emil Axelsson 78emil at gmail.com
Wed Oct 13 19:22:55 UTC 2021

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/ Emil

Den 2021-10-12 kl. 21:35, skrev Benjamin Redelings:
> Hi,
> 1. I'm looking for resources that describe how to implement kind 
> Haskell 98 checking.  Does anyone have any suggestions?
> * I've looked at the PolyKinds paper, but it doesn't cover type classes.
> * I've looked at the source code to GHC, but it is hard to follow for 
> a variety of reasons.  It isn't laid out like an algorithm 
> description, and the complexity to handle options like PolyKinds and 
> DataKinds makes the code harder to follow.
> 2. One question that came up is how to handle type variables that are 
> present in class methods, but are not type class parameters. If there 
> are multiple types/classes in a single recursive group, the kind of 
> such type variables might not be fully resolved until a later 
> type-or-class is processed.  Is there a recommended approach?
> I can see two ways to proceed:
> i) First determine the kinds of all the data types, classes, and type 
> synonyms.  Then perform a second pass over each type or class to 
> determine the kinds of type variables (in class methods) that are not 
> type class parameters.
> ii) Alternatively, record the kind of each type variable as it is 
> encountered -- even though such kinds may contain unification kind 
> variables.  After visiting all types-or-classes in the recursive 
> group, replace any kind variables with their definition, or with a * 
> if there is no definition.
> I've currently implement approach i), which requires doing kind 
> inference on class methods twice.  Is this the recommended approach?
> 3. Also, is Haskell 98 kind checking the same as Haskell 2010 kind 
> checking?
> -BenRI
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