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Alan Zimmerman authored
Summary: See https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow This commit prepares the ground for a full extensible AST, by replacing the type parameter for the hsSyn data types with a set of indices into type families, data GhcPs -- ^ Index for GHC parser output data GhcRn -- ^ Index for GHC renamer output data GhcTc -- ^ Index for GHC typechecker output These are now used instead of `RdrName`, `Name` and `Id`/`TcId`/`Var` Where the original name type is required in a polymorphic context, this is accessible via the IdP type family, defined as type family IdP p type instance IdP GhcPs = RdrName type instance IdP GhcRn = Name type instance IdP GhcTc = Id These types are declared in the new 'hsSyn/HsExtension.hs' module. To gain a better understanding of the extension mechanism, it has been applied to `HsLit` only, also replacing the `SourceText` fields in them with extension types. To preserve extension generality, a type class is introduced to capture the `SourceText` interface, which must be honoured by all of the extension points which originally had a `SourceText`. The class is defined as class HasSourceText a where -- Provide setters to mimic existing constructors noSourceText :: a sourceText :: String -> a setSourceText :: SourceText -> a getSourceText :: a -> SourceText And the constraint is captured in `SourceTextX`, which is a constraint type listing all the extension points that make use of the class. Updating Haddock submodule to match. Test Plan: ./validate Reviewers: simonpj, shayan-najd, goldfire, austin, bgamari Subscribers: rwbarton, thomie, mpickering Differential Revision: https://phabricator.haskell.org/D3609
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