import HsSyn ( Stmt(..), HsExpr(..), GRHSs(..), GRHS(..),
HsMatchContext(..), Pat(..) )
import CoreSyn ( CoreExpr )
-import Type ( Type )
import Var ( Id )
+import Type ( Type )
import DsMonad
import DsUtils
necessary. The type argument gives the type of the @ei@.
\begin{code}
-dsGuarded :: GRHSs Id -> DsM CoreExpr
+dsGuarded :: GRHSs Id -> Type -> DsM CoreExpr
-dsGuarded grhss
- = dsGRHSs PatBindRhs [] grhss `thenDs` \ (err_ty, match_result) ->
- mkErrorAppDs nON_EXHAUSTIVE_GUARDS_ERROR_ID err_ty "" `thenDs` \ error_expr ->
+dsGuarded grhss rhs_ty
+ = dsGRHSs PatBindRhs [] grhss rhs_ty `thenDs` \ match_result ->
+ mkErrorAppDs nON_EXHAUSTIVE_GUARDS_ERROR_ID rhs_ty "" `thenDs` \ error_expr ->
extractMatchResult match_result error_expr
\end{code}
\begin{code}
dsGRHSs :: HsMatchContext Name -> [Pat Id] -- These are to build a MatchContext from
-> GRHSs Id -- Guarded RHSs
- -> DsM (Type, MatchResult)
+ -> Type -- Type of RHS
+ -> DsM MatchResult
-dsGRHSs kind pats (GRHSs grhss binds ty)
- = mappM (dsGRHS kind pats) grhss `thenDs` \ match_results ->
+dsGRHSs kind pats (GRHSs grhss binds) rhs_ty
+ = mappM (dsGRHS kind pats rhs_ty) grhss `thenDs` \ match_results ->
let
match_result1 = foldr1 combineMatchResults match_results
match_result2 = adjustMatchResultDs (dsLet binds) match_result1
-- NB: nested dsLet inside matchResult
in
- returnDs (ty, match_result2)
+ returnDs match_result2
-dsGRHS kind pats (L loc (GRHS guard))
- = matchGuard (map unLoc guard) (DsMatchContext kind pats loc)
+dsGRHS kind pats rhs_ty (L loc (GRHS guard))
+ = matchGuard (map unLoc guard) (DsMatchContext kind pats loc) rhs_ty
\end{code}
\begin{code}
matchGuard :: [Stmt Id] -- Guard
- -> DsMatchContext -- Context
+ -> DsMatchContext -- Context
+ -> Type -- Type of RHS of guard
-> DsM MatchResult
-- See comments with HsExpr.Stmt re what an ExprStmt means
-- Here we must be in a guard context (not do-expression, nor list-comp)
-matchGuard [ResultStmt expr] ctx
- = dsLExpr expr `thenDs` \ core_expr ->
- returnDs (cantFailMatchResult core_expr)
+matchGuard [ResultStmt expr] ctx rhs_ty
+ = do { core_expr <- dsLExpr expr
+ ; return (cantFailMatchResult core_expr) }
-- ExprStmts must be guards
-- Turn an "otherwise" guard is a no-op
-matchGuard (ExprStmt (L _ (HsVar v)) _ : stmts) ctx
+matchGuard (ExprStmt (L _ (HsVar v)) _ : stmts) ctx rhs_ty
| v `hasKey` otherwiseIdKey
|| v `hasKey` getUnique trueDataConId
-- trueDataConId doesn't have the same
-- unique as trueDataCon
- = matchGuard stmts ctx
+ = matchGuard stmts ctx rhs_ty
-matchGuard (ExprStmt expr _ : stmts) ctx
- = matchGuard stmts ctx `thenDs` \ match_result ->
+matchGuard (ExprStmt expr _ : stmts) ctx rhs_ty
+ = matchGuard stmts ctx rhs_ty `thenDs` \ match_result ->
dsLExpr expr `thenDs` \ pred_expr ->
returnDs (mkGuardedMatchResult pred_expr match_result)
-matchGuard (LetStmt binds : stmts) ctx
- = matchGuard stmts ctx `thenDs` \ match_result ->
+matchGuard (LetStmt binds : stmts) ctx rhs_ty
+ = matchGuard stmts ctx rhs_ty `thenDs` \ match_result ->
returnDs (adjustMatchResultDs (dsLet binds) match_result)
-- NB the dsLet occurs inside the match_result
-
-matchGuard (BindStmt pat rhs : stmts) ctx
- = matchGuard stmts ctx `thenDs` \ match_result ->
- dsLExpr rhs `thenDs` \ core_rhs ->
- matchSinglePat core_rhs ctx pat match_result
+ -- Reason: dsLet takes the body expression as its argument
+ -- so we can't desugar the bindings without the
+ -- body expression in hand
+
+matchGuard (BindStmt pat bind_rhs : stmts) ctx rhs_ty
+ = matchGuard stmts ctx rhs_ty `thenDs` \ match_result ->
+ dsLExpr bind_rhs `thenDs` \ core_rhs ->
+ matchSinglePat core_rhs ctx pat rhs_ty match_result
\end{code}
Should {\em fail} if @e@ returns @D@