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

Benjamin Redelings benjamin.redelings at gmail.com
Tue Oct 12 19:35:22 UTC 2021


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?


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