+checkLastStmt :: HsStmtContext Name
+ -> LStmt RdrName
+ -> RnM (LStmt RdrName)
+checkLastStmt ctxt lstmt@(L loc stmt)
+ = case ctxt of
+ ListComp -> check_comp
+ MonadComp -> check_comp
+ PArrComp -> check_comp
+ DoExpr -> check_do
+ MDoExpr -> check_do
+ _ -> check_other
+ where
+ check_do -- Expect ExprStmt, and change it to LastStmt
+ = case stmt of
+ ExprStmt e _ _ _ -> return (L loc (mkLastStmt e))
+ LastStmt {} -> return lstmt -- "Deriving" clauses may generate a
+ -- LastStmt directly (unlike the parser)
+ _ -> do { addErr (hang last_error 2 (ppr stmt)); return lstmt }
+ last_error = (ptext (sLit "The last statement in") <+> pprAStmtContext ctxt
+ <+> ptext (sLit "must be an expression"))
+
+ check_comp -- Expect LastStmt; this should be enforced by the parser!
+ = case stmt of
+ LastStmt {} -> return lstmt
+ _ -> pprPanic "checkLastStmt" (ppr lstmt)
+
+ check_other -- Behave just as if this wasn't the last stmt
+ = do { checkStmt ctxt lstmt; return lstmt }
+