Version 5 (modified by ia0, 6 years ago) (diff)

add a changelog

GHC Kind level

This page gives the theory, implementation overview and details about GHC's kind level. This work is related to Conor's SHE system and will be related to Iavor's work on TypeNats to deal with primitive types (promoted Int and Char).


We use the mechanism of promotion to lift a data type to the kind level. This gives access at the type level to the data constructors, and at the kind level to the type constructor. All data types cannot be promoted. For examples GADTs or data types with higher-order kinds. We add kind polymorphism to allow promotion of polymorphic data constructors (like Nil or Cons).

More details can be found in this theory pdf.


Examples of reimplementation of existing Haskell librairies can be found in this examples pdf.


The branch is called ghc-kinds. Its current state is:

ADT promotion Primitives Kind polymorphism
Parser Yes Yes Yes
Renamer In progress Yes

Promotion-related changelog:

  • Change the kind representation in HsSyn from Kind to LHsKind name adding some PostTcKind when necessary.
    • Rename rnHsType into rnHsTyKi and parametrize with a boolean to know if we are renaming a type or a kind.
  • Allow promoted data and type constructors:
    • Extend the parser to allow ticked names like 'Zero or 'Nat.Succ as atoms in types.
    • Extend the parser to allow optionally ticked names like Nat or 'Bool as atoms in kinds.
    • Extend HsType name with HsPromotedConTy name to represent ticked names.
    • Extend TyCon with PromotedDataTyCon to represent promoted data constructors.
  • Rename KindVar which is used during type checking into MetaKindVar, since we will add kind variables later.

Not promotion-related changelog:

  • Use HsDocContext instead of SDoc to track renaming context.

The stage1 compiler does not work, since there is some undefineds in the typechecker. So you won't be able to build a stage2 or even run validate. This is the first priority.