diff options
Diffstat (limited to 'compiler/GHC/Rename/Expr.hs')
| -rw-r--r-- | compiler/GHC/Rename/Expr.hs | 44 |
1 files changed, 40 insertions, 4 deletions
diff --git a/compiler/GHC/Rename/Expr.hs b/compiler/GHC/Rename/Expr.hs index 055afd7e84..0323998ecb 100644 --- a/compiler/GHC/Rename/Expr.hs +++ b/compiler/GHC/Rename/Expr.hs @@ -23,7 +23,7 @@ free variables. -} module GHC.Rename.Expr ( - rnLExpr, rnExpr, rnStmts, + rnLExpr, rnExpr, rnStmts, mkExpandedExpr, AnnoBody ) where @@ -151,6 +151,41 @@ but several have a little bit of special treatment: on the fly, in GHC.Tc.Gen.Head.splitHsApps. RebindableSyntax does not affect this. +* RecordUpd: we desugar record updates into case expressions, + in GHC.Tc.Gen.Expr.tcExpr. + + Example: + + data T p q = T1 { x :: Int, y :: Bool, z :: Char } + | T2 { v :: Char } + | T3 { x :: Int } + | T4 { p :: Float, y :: Bool, x :: Int } + | T5 + + e { x=e1, y=e2 } + ===> + let { x' = e1; y' = e2 } in + case e of + T1 _ _ z -> T1 x' y' z + T4 p _ _ -> T4 p y' x' + + See Note [Record Updates] in GHC.Tc.Gen.Expr for more details. + + This is done in the typechecker, not the renamer, for two reasons: + + - (Until we implement GHC proposal #366) + We need to know the type of the record to disambiguate its fields. + + - We use the type signature of the data constructor to provide IdSigs + to the let-bound variables (x', y' in the example above). This is + needed to accept programs such as + + data R b = MkR { f :: (forall a. a -> a) -> (Int,b), c :: Int } + foo r = r { f = \ k -> (k 3, k 'x') } + + in which an updated field has a higher-rank type. + See Wrinkle [Using IdSig] in Note [Record Updates] in GHC.Tc.Gen.Expr. + Note [Overloaded labels] ~~~~~~~~~~~~~~~~~~~~~~~~ For overloaded labels, note that we /only/ apply `fromLabel` to the @@ -1154,9 +1189,10 @@ rnStmt ctxt rnBody (L loc (RecStmt { recS_stmts = L _ rec_stmts })) thing_inside = do { (return_op, fvs1) <- lookupQualifiedDoStmtName ctxt returnMName ; (mfix_op, fvs2) <- lookupQualifiedDoStmtName ctxt mfixName ; (bind_op, fvs3) <- lookupQualifiedDoStmtName ctxt bindMName - ; let empty_rec_stmt = emptyRecStmtName { recS_ret_fn = return_op - , recS_mfix_fn = mfix_op - , recS_bind_fn = bind_op } + ; let empty_rec_stmt = (emptyRecStmtName :: StmtLR GhcRn GhcRn (LocatedA (body GhcRn))) + { recS_ret_fn = return_op + , recS_mfix_fn = mfix_op + , recS_bind_fn = bind_op } -- Step1: Bring all the binders of the mdo into scope -- (Remember that this also removes the binders from the |