Cannot compute type fingerprint in plugin, kinds/types are mixed

Nicolas Frisby nicolas.frisby at
Tue May 22 15:52:11 UTC 2018

Hi Alice.

I'm having trouble following your question -- I'm not familiar with the
internals of fingerprint generation.

But, have you scoured the compiler/typecheck/TcTypeable.hs file? It seems
likely to have similar logic to what you seem to be seeking.

HTH. -Nick

On Tue, May 22, 2018, 06:38 alice <alicekoroleva239 at> wrote:

> Hello again. I’m trying to make a function in a type-checking plugin that
> takes TyCoRep#Type and makes its fingerprint that matches
> `typeRepFingerprint (typeRep :: TypeRep (type))`. As I understood the
> type’s fingerprint is made in DsBinds#dsEvTypeable by generating a code
> that makes the fingerprint, so I can’t reuse functions which are already
> written.
> My goal is to write a function that makes fingerprints of types which are
> not type variables such as Int, Maybe Int, ‘[Int] etc. So I tried to follow
> `mkTrCon` and `mkTrApp` style, and I think I managed to process simple
> types like Int, Maybe Int — right now I’m processing TyConApp only. But
> when I tried to make promoted data fingerprint like ‘[Int] I faced some
> problems.
> For example, for making `’Just Int` fingerprint first I have to compute
> 'Just fingerprint by computing  'Just tyCon’s and * fingerprints, then
> combining them into one fingerprint. Then I have to apply ‘Just to Int. But
> when I try to do something like that while type checking I cannot separate
> two cases that match runtime’s`TypeRep (a b)` (a representation for a type
> application) and `TypeRep a` (a representation for a type constructor)
> because they are represented by TyConApp. Also I can’t separate tyCon kinds
> and types for type application because they are merged into one list which
> is stored in `TyConApp _ [KindOrType]`. [KindOrType] list for `’Just Int`
> is `[*, Int]`. Is there any way to separate this two cases and kinds/types?
> Probably there is an easier way to make this function? If not, does type
> fingerprint function seem possible to make?
> Any help would be appreciated,
> Alice.
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