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Diffstat (limited to 'docs/users_guide/8.4.1-notes.rst')
| -rw-r--r-- | docs/users_guide/8.4.1-notes.rst | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/docs/users_guide/8.4.1-notes.rst b/docs/users_guide/8.4.1-notes.rst index 72d6901d18..5929998e95 100644 --- a/docs/users_guide/8.4.1-notes.rst +++ b/docs/users_guide/8.4.1-notes.rst @@ -94,3 +94,37 @@ Template Haskell ``ghc`` library ~~~~~~~~~~~~~~~ + +- hsSyn Abstract Syntax Tree (AST) is now extensible via the mechanism described in `Trees that Grow <http://www.jucs.org/jucs_23_1/trees_that_grow/jucs_23_01_0042_0062_najd.pdf>`_ + + The main change for users of the GHC API is that the AST is no longer indexed + by the type used as the identifier, but by a specific index type, :: + + type GhcPs = GhcPass 'Parsed -- Old 'RdrName' type param + type GhcRn = GhcPass 'Renamed -- Old 'Name' type param + type GhcTc = GhcPass 'Typechecked -- Old 'Id' type para, + type GhcTcId = GhcTc -- Old 'TcId' type param + + The simplest way to support the current GHC as well as earlier ones is to define :: + + #if MIN_VERSION_ghc(8,3,0) + type ParseI = GhcPs + type RenameI = GhcRn + type TypecheckI = GhcTc + #else + type ParseI = RdrName + type RenameI = Name + type TypecheckI = Var + #endif + + and then replace all hardcoded index types accordingly. For polymorphic types, + the constraint :: + + #if MIN_VERSION_ghc(8,3,0) + -- |bundle up the constraints required for a trees that grow pass + type IsPass pass = (DataId pass, OutputableBndrId pass, SourceTextX pass) + else + type IsPass pass = (DataId pass, OutputableBndrId pass) + #endif + + can be used. |