{
  "$type": "site.standard.document",
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  "path": "/t/history-of-dh-dependent-types-in-haskell-contributions/11242?page=2#post_25",
  "publishedAt": "2026-03-29T02:01:15.000Z",
  "site": "https://discourse.haskell.org",
  "textContent": "Here’s a probably stupid idea I had for unification:\n\nUse a type family that would redirect the term specific things. E.g.\n\n\n    data HsTerm s p =\n        -- Variations of\n    HsVar/HsTyVar\n    HsOverLit, HsLit/HsTyLit\n    HsApp/HsAppTy\n    HsAppType/HsAppKindTy\n    OpApp/HsOpTy\n    HsPar/HsParTy\n    ExplicitTuple/HsExplicitTupleTy\n    ExplicitList/HsExplicitListTy\n    ExprWithTySig/HsKindSig\n    HsUntypedSplice/HsSpliceTy\n    HsHole/HsWildCardTy\n    HsForAll/HsForAllTy\n    HsQual/HsQualTy\n    HsFunArr/HsFunTy\n        -- The redirect\n        HsExprType !(XHsExprType s p) (ExprType s p)\n\n    data TermParam = Ty | Ex | Unknown -- like this to avoid name collisions in GHC, qualified imports would probably be used.\n\n    type family ExprType where\n        ExprType Ty = OtherHsType\n        ExprType Ex = OtherHsExpr\n        ExprType Unknown= DataCannotHappen\n    type HsExpr = HsTerm Ex\n    type HsType = HsTerm Ty\n\n\nWhere `OtherHsType` and `OtherHsExpr` contain fields not mentioned above. I mainly propose this as with `PatternSynonyms`, I don’t think it’s a breaking change.\n\n(Sorry for the formatting, I’ll change it when I’m at my computer)",
  "title": "History of DH (Dependent Types in Haskell) contributions"
}