\section[DsExpr]{Matching expressions (Exprs)}
\begin{code}
-module DsExpr ( dsExpr, dsLExpr, dsLet, dsLit ) where
+module DsExpr ( dsExpr, dsLExpr, dsLocalBinds, dsValBinds, dsLit ) where
#include "HsVersions.h"
-
-import Match ( matchWrapper, matchSimply )
-import MatchLit ( dsLit )
-import DsBinds ( dsHsNestedBinds )
+import Match ( matchWrapper, matchSinglePat, matchEquations )
+import MatchLit ( dsLit, dsOverLit )
+import DsBinds ( dsLHsBinds, dsCoercion )
import DsGRHSs ( dsGuarded )
import DsListComp ( dsListComp, dsPArrComp )
import DsUtils ( mkErrorAppDs, mkStringExpr, mkConsExpr, mkNilExpr,
- mkCoreTupTy, selectSimpleMatchVarL,
- dsReboundNames, lookupReboundName )
+ extractMatchResult, cantFailMatchResult, matchCanFail,
+ mkCoreTupTy, selectSimpleMatchVarL, lookupEvidence, selectMatchVar )
import DsArrows ( dsProcExpr )
import DsMonad
#endif
import HsSyn
-import TcHsSyn ( hsPatType )
+import TcHsSyn ( hsPatType, mkVanillaTuplePat )
-- NB: The desugarer, which straddles the source and Core worlds, sometimes
-- needs to see source types (newtypes etc), and sometimes not
-- So WATCH OUT; check each use of split*Ty functions.
-- Sigh. This is a pain.
-import TcType ( tcSplitAppTy, tcSplitFunTys, tcTyConAppTyCon, tcTyConAppArgs,
+import TcType ( tcSplitAppTy, tcSplitFunTys, tcTyConAppTyCon,
tcTyConAppArgs, isUnLiftedType, Type, mkAppTy )
-import Type ( mkFunTys, funArgTy, splitFunTys, isUnboxedTupleType, mkFunTy )
+import Type ( funArgTy, splitFunTys, isUnboxedTupleType, mkFunTy )
import CoreSyn
import CoreUtils ( exprType, mkIfThenElse, bindNonRec )
import CostCentre ( mkUserCC )
-import Id ( Id, idType, idName )
+import Id ( Id, idType, idName, idDataCon )
import PrelInfo ( rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID )
import DataCon ( DataCon, dataConWrapId, dataConFieldLabels, dataConInstOrigArgTys )
import DataCon ( isVanillaDataCon )
-import Name ( Name )
import TyCon ( FieldLabel, tyConDataCons )
import TysWiredIn ( tupleCon )
import BasicTypes ( RecFlag(..), Boxity(..), ipNameName )
%************************************************************************
%* *
-\subsection{dsLet}
+ dsLocalBinds, dsValBinds
%* *
%************************************************************************
-@dsLet@ is a match-result transformer, taking the @MatchResult@ for the body
-and transforming it into one for the let-bindings enclosing the body.
-
-This may seem a bit odd, but (source) let bindings can contain unboxed
-binds like
-\begin{verbatim}
- C x# = e
-\end{verbatim}
-This must be transformed to a case expression and, if the type has
-more than one constructor, may fail.
-
\begin{code}
-dsLet :: [HsBindGroup Id] -> CoreExpr -> DsM CoreExpr
-dsLet groups body = foldlDs dsBindGroup body (reverse groups)
-
-dsBindGroup :: CoreExpr -> HsBindGroup Id -> DsM CoreExpr
-dsBindGroup body (HsIPBinds binds)
- = foldlDs dsIPBind body binds
+dsLocalBinds :: HsLocalBinds Id -> CoreExpr -> DsM CoreExpr
+dsLocalBinds EmptyLocalBinds body = return body
+dsLocalBinds (HsValBinds binds) body = dsValBinds binds body
+dsLocalBinds (HsIPBinds binds) body = dsIPBinds binds body
+
+-------------------------
+dsValBinds :: HsValBinds Id -> CoreExpr -> DsM CoreExpr
+dsValBinds (ValBindsOut binds _) body = foldrDs ds_val_bind body binds
+
+-------------------------
+dsIPBinds (IPBinds ip_binds dict_binds) body
+ = do { prs <- dsLHsBinds dict_binds
+ ; let inner = foldr (\(x,r) e -> Let (NonRec x r) e) body prs
+ ; foldrDs ds_ip_bind inner ip_binds }
where
- dsIPBind body (L _ (IPBind n e))
- = dsLExpr e `thenDs` \ e' ->
- returnDs (Let (NonRec (ipNameName n) e') body)
+ ds_ip_bind (L _ (IPBind n e)) body
+ = dsLExpr e `thenDs` \ e' ->
+ returnDs (Let (NonRec (ipNameName n) e') body)
+-------------------------
+ds_val_bind :: (RecFlag, LHsBinds Id) -> CoreExpr -> DsM CoreExpr
-- Special case for bindings which bind unlifted variables
-- We need to do a case right away, rather than building
-- a tuple and doing selections.
--- Silently ignore INLINE pragmas...
-dsBindGroup body bind@(HsBindGroup hsbinds sigs is_rec)
- | [L _ (AbsBinds [] [] exports inlines binds)] <- bagToList hsbinds,
- or [isUnLiftedType (idType g) | (_, g, l) <- exports]
- = ASSERT (case is_rec of {NonRecursive -> True; other -> False})
- -- Unlifted bindings are always non-recursive
- -- and are always a Fun or Pat monobind
- --
+-- Silently ignore INLINE and SPECIALISE pragmas...
+ds_val_bind (NonRecursive, hsbinds) body
+ | [L _ (AbsBinds [] [] exports binds)] <- bagToList hsbinds,
+ (L loc bind : null_binds) <- bagToList binds,
+ isBangHsBind bind
+ || isUnboxedTupleBind bind
+ || or [isUnLiftedType (idType g) | (_, g, _, _) <- exports]
+ = let
+ body_w_exports = foldr bind_export body exports
+ bind_export (tvs, g, l, _) body = ASSERT( null tvs )
+ bindNonRec g (Var l) body
+ in
+ ASSERT (null null_binds)
+ -- Non-recursive, non-overloaded bindings only come in ones
-- ToDo: in some bizarre case it's conceivable that there
-- could be dict binds in the 'binds'. (See the notes
-- below. Then pattern-match would fail. Urk.)
- let
- body_w_exports = foldr bind_export body exports
- bind_export (tvs, g, l) body = ASSERT( null tvs )
- bindNonRec g (Var l) body
-
- mk_error_app pat = mkErrorAppDs iRREFUT_PAT_ERROR_ID
- (exprType body)
- (showSDoc (ppr pat))
- in
- case bagToList binds of
- [L loc (FunBind (L _ fun) _ matches)]
- -> putSrcSpanDs loc $
- matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, rhs) ->
+ putSrcSpanDs loc $
+ case bind of
+ FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn }
+ -> matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, rhs) ->
ASSERT( null args ) -- Functions aren't lifted
+ ASSERT( isIdCoercion co_fn )
returnDs (bindNonRec fun rhs body_w_exports)
- [L loc (PatBind pat grhss ty)]
- -> putSrcSpanDs loc $
- dsGuarded grhss ty `thenDs` \ rhs ->
- mk_error_app pat `thenDs` \ error_expr ->
- matchSimply rhs PatBindRhs pat body_w_exports error_expr
-
- other -> pprPanic "dsLet: unlifted" (ppr bind $$ ppr body)
-
--- Ordinary case for bindings
-dsBindGroup body (HsBindGroup binds sigs is_rec)
- = dsHsNestedBinds binds `thenDs` \ prs ->
- returnDs (Let (Rec prs) body)
+ PatBind {pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }
+ -> -- let C x# y# = rhs in body
+ -- ==> case rhs of C x# y# -> body
+ putSrcSpanDs loc $
+ do { rhs <- dsGuarded grhss ty
+ ; let upat = unLoc pat
+ eqn = EqnInfo { eqn_wrap = idWrapper, eqn_pats = [upat],
+ eqn_rhs = cantFailMatchResult body_w_exports }
+ ; var <- selectMatchVar upat ty
+ ; result <- matchEquations PatBindRhs [var] [eqn] (exprType body)
+ ; return (scrungleMatch var rhs result) }
+
+ other -> pprPanic "dsLet: unlifted" (pprLHsBinds hsbinds $$ ppr body)
+
+
+-- Ordinary case for bindings; none should be unlifted
+ds_val_bind (is_rec, binds) body
+ = do { prs <- dsLHsBinds binds
+ ; ASSERT( not (any (isUnLiftedType . idType . fst) prs) )
+ case prs of
+ [] -> return body
+ other -> return (Let (Rec prs) body) }
-- Use a Rec regardless of is_rec.
-- Why? Because it allows the binds to be all
-- mixed up, which is what happens in one rare case
--
-- NB The previous case dealt with unlifted bindings, so we
-- only have to deal with lifted ones now; so Rec is ok
+
+isUnboxedTupleBind :: HsBind Id -> Bool
+isUnboxedTupleBind (PatBind { pat_rhs_ty = ty }) = isUnboxedTupleType ty
+isUnboxedTupleBind other = False
+
+scrungleMatch :: Id -> CoreExpr -> CoreExpr -> CoreExpr
+-- Returns something like (let var = scrut in body)
+-- but if var is an unboxed-tuple type, it inlines it in a fragile way
+-- Special case to handle unboxed tuple patterns; they can't appear nested
+-- The idea is that
+-- case e of (# p1, p2 #) -> rhs
+-- should desugar to
+-- case e of (# x1, x2 #) -> ... match p1, p2 ...
+-- NOT
+-- let x = e in case x of ....
+--
+-- But there may be a big
+-- let fail = ... in case e of ...
+-- wrapping the whole case, which complicates matters slightly
+-- It all seems a bit fragile. Test is dsrun013.
+
+scrungleMatch var scrut body
+ | isUnboxedTupleType (idType var) = scrungle body
+ | otherwise = bindNonRec var scrut body
+ where
+ scrungle (Case (Var x) bndr ty alts)
+ | x == var = Case scrut bndr ty alts
+ scrungle (Let binds body) = Let binds (scrungle body)
+ scrungle other = panic ("scrungleMatch: tuple pattern:\n" ++ showSDoc (ppr other))
\end{code}
%************************************************************************
dsExpr (HsPar e) = dsLExpr e
dsExpr (ExprWithTySigOut e _) = dsLExpr e
-dsExpr (HsVar var) = returnDs (Var var)
-dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
-dsExpr (HsLit lit) = dsLit lit
--- HsOverLit has been gotten rid of by the type checker
+dsExpr (HsVar var) = returnDs (Var var)
+dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
+dsExpr (HsLit lit) = dsLit lit
+dsExpr (HsOverLit lit) = dsOverLit lit
+
+dsExpr (NegApp expr neg_expr)
+ = do { core_expr <- dsLExpr expr
+ ; core_neg <- dsExpr neg_expr
+ ; return (core_neg `App` core_expr) }
dsExpr expr@(HsLam a_Match)
= matchWrapper LambdaExpr a_Match `thenDs` \ (binders, matching_code) ->
= dsLExpr expr `thenDs` \ core_expr ->
returnDs (Note (CoreNote $ unpackFS fs) core_expr)
--- Special case to handle unboxed tuple patterns; they can't appear nested
-dsExpr (HsCase discrim matches@(MatchGroup _ ty))
- | isUnboxedTupleType (funArgTy ty)
- = dsLExpr discrim `thenDs` \ core_discrim ->
- matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
- case matching_code of
- Case (Var x) bndr ty alts | x == discrim_var ->
- returnDs (Case core_discrim bndr ty alts)
- _ -> panic ("dsLExpr: tuple pattern:\n" ++ showSDoc (ppr matching_code))
-
dsExpr (HsCase discrim matches)
= dsLExpr discrim `thenDs` \ core_discrim ->
matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
- returnDs (bindNonRec discrim_var core_discrim matching_code)
+ returnDs (scrungleMatch discrim_var core_discrim matching_code)
dsExpr (HsLet binds body)
= dsLExpr body `thenDs` \ body' ->
- dsLet binds body'
+ dsLocalBinds binds body'
-- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
-- because the interpretation of `stmts' depends on what sort of thing it is.
--
-dsExpr (HsDo ListComp stmts _ result_ty)
+dsExpr (HsDo ListComp stmts body result_ty)
= -- Special case for list comprehensions
- dsListComp stmts elt_ty
+ dsListComp stmts body elt_ty
where
[elt_ty] = tcTyConAppArgs result_ty
-dsExpr (HsDo do_or_lc stmts ids result_ty)
- | isDoExpr do_or_lc
- = dsDo do_or_lc stmts ids result_ty
+dsExpr (HsDo DoExpr stmts body result_ty)
+ = dsDo stmts body result_ty
+
+dsExpr (HsDo (MDoExpr tbl) stmts body result_ty)
+ = dsMDo tbl stmts body result_ty
-dsExpr (HsDo PArrComp stmts _ result_ty)
+dsExpr (HsDo PArrComp stmts body result_ty)
= -- Special case for array comprehensions
- dsPArrComp (map unLoc stmts) elt_ty
+ dsPArrComp (map unLoc stmts) body elt_ty
where
[elt_ty] = tcTyConAppArgs result_ty
-- we create a list from the array elements and convert them into a list using
-- `PrelPArr.toP'
--
--- * the main disadvantage to this scheme is that `toP' traverses the list
+-- * the main disadvantage to this scheme is that `toP' traverses the list
-- twice: once to determine the length and a second time to put to elements
-- into the array; this inefficiency could be avoided by exposing some of
-- the innards of `PrelPArr' to the compiler (ie, have a `PrelPArrBase') so
returnDs (mkConApp (tupleCon boxity (length expr_list))
(map (Type . exprType) core_exprs ++ core_exprs))
-dsExpr (ArithSeqOut expr (From from))
- = dsLExpr expr `thenDs` \ expr2 ->
- dsLExpr from `thenDs` \ from2 ->
+dsExpr (ArithSeq expr (From from))
+ = dsExpr expr `thenDs` \ expr2 ->
+ dsLExpr from `thenDs` \ from2 ->
returnDs (App expr2 from2)
-dsExpr (ArithSeqOut expr (FromTo from two))
- = dsLExpr expr `thenDs` \ expr2 ->
- dsLExpr from `thenDs` \ from2 ->
+dsExpr (ArithSeq expr (FromTo from two))
+ = dsExpr expr `thenDs` \ expr2 ->
+ dsLExpr from `thenDs` \ from2 ->
dsLExpr two `thenDs` \ two2 ->
returnDs (mkApps expr2 [from2, two2])
-dsExpr (ArithSeqOut expr (FromThen from thn))
- = dsLExpr expr `thenDs` \ expr2 ->
- dsLExpr from `thenDs` \ from2 ->
+dsExpr (ArithSeq expr (FromThen from thn))
+ = dsExpr expr `thenDs` \ expr2 ->
+ dsLExpr from `thenDs` \ from2 ->
dsLExpr thn `thenDs` \ thn2 ->
returnDs (mkApps expr2 [from2, thn2])
-dsExpr (ArithSeqOut expr (FromThenTo from thn two))
- = dsLExpr expr `thenDs` \ expr2 ->
- dsLExpr from `thenDs` \ from2 ->
+dsExpr (ArithSeq expr (FromThenTo from thn two))
+ = dsExpr expr `thenDs` \ expr2 ->
+ dsLExpr from `thenDs` \ from2 ->
dsLExpr thn `thenDs` \ thn2 ->
dsLExpr two `thenDs` \ two2 ->
returnDs (mkApps expr2 [from2, thn2, two2])
-dsExpr (PArrSeqOut expr (FromTo from two))
- = dsLExpr expr `thenDs` \ expr2 ->
- dsLExpr from `thenDs` \ from2 ->
+dsExpr (PArrSeq expr (FromTo from two))
+ = dsExpr expr `thenDs` \ expr2 ->
+ dsLExpr from `thenDs` \ from2 ->
dsLExpr two `thenDs` \ two2 ->
returnDs (mkApps expr2 [from2, two2])
-dsExpr (PArrSeqOut expr (FromThenTo from thn two))
- = dsLExpr expr `thenDs` \ expr2 ->
- dsLExpr from `thenDs` \ from2 ->
+dsExpr (PArrSeq expr (FromThenTo from thn two))
+ = dsExpr expr `thenDs` \ expr2 ->
+ dsLExpr from `thenDs` \ from2 ->
dsLExpr thn `thenDs` \ thn2 ->
dsLExpr two `thenDs` \ two2 ->
returnDs (mkApps expr2 [from2, thn2, two2])
-dsExpr (PArrSeqOut expr _)
+dsExpr (PArrSeq expr _)
= panic "DsExpr.dsExpr: Infinite parallel array!"
-- the parser shouldn't have generated it and the renamer and typechecker
-- shouldn't have let it through
constructor @C@, setting all of @C@'s fields to bottom.
\begin{code}
-dsExpr (RecordConOut data_con con_expr rbinds)
- = dsLExpr con_expr `thenDs` \ con_expr' ->
+dsExpr (RecordCon (L _ data_con_id) con_expr rbinds)
+ = dsExpr con_expr `thenDs` \ con_expr' ->
let
(arg_tys, _) = tcSplitFunTys (exprType con_expr')
-- A newtype in the corner should be opaque;
[] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
- labels = dataConFieldLabels data_con
+ labels = dataConFieldLabels (idDataCon data_con_id)
+ -- The data_con_id is guaranteed to be the wrapper id of the constructor
in
(if null labels
dictionaries.
\begin{code}
-dsExpr (RecordUpdOut record_expr record_in_ty record_out_ty [])
+dsExpr (RecordUpd record_expr [] record_in_ty record_out_ty)
= dsLExpr record_expr
-dsExpr expr@(RecordUpdOut record_expr record_in_ty record_out_ty rbinds)
+dsExpr expr@(RecordUpd record_expr rbinds record_in_ty record_out_ty)
= dsLExpr record_expr `thenDs` \ record_expr' ->
-- Desugar the rbinds, and generate let-bindings if
mk_alt con
= newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys) `thenDs` \ arg_ids ->
- -- This call to dataConArgTys won't work for existentials
+ -- This call to dataConInstOrigArgTys won't work for existentials
-- but existentials don't have record types anyway
let
val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
dsExpr (DictApp expr dicts) -- becomes a curried application
= dsLExpr expr `thenDs` \ core_expr ->
returnDs (foldl (\f d -> f `App` (Var d)) core_expr dicts)
+
+dsExpr (HsCoerce co_fn e) = dsCoercion co_fn (dsExpr e)
\end{code}
Here is where we desugar the Template Haskell brackets and escapes
#ifdef DEBUG
-- HsSyn constructs that just shouldn't be here:
dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
-dsExpr (ArithSeqIn _) = panic "dsExpr:ArithSeqIn"
-dsExpr (PArrSeqIn _) = panic "dsExpr:PArrSeqIn"
#endif
\end{code}
Haskell 98 report:
\begin{code}
-dsDo :: HsStmtContext Name
- -> [LStmt Id]
- -> ReboundNames Id -- id for: [return,fail,>>=,>>] and possibly mfixName
- -> Type -- Element type; the whole expression has type (m t)
+dsDo :: [LStmt Id]
+ -> LHsExpr Id
+ -> Type -- Type of the whole expression
-> DsM CoreExpr
-dsDo do_or_lc stmts ids result_ty
- = dsReboundNames ids `thenDs` \ (meth_binds, ds_meths) ->
- let
- fail_id = lookupReboundName ds_meths failMName
- bind_id = lookupReboundName ds_meths bindMName
- then_id = lookupReboundName ds_meths thenMName
-
- (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
-
- -- For ExprStmt, see the comments near HsExpr.Stmt about
- -- exactly what ExprStmts mean!
- --
- -- In dsDo we can only see DoStmt and ListComp (no guards)
-
- go [ResultStmt expr] = dsLExpr expr
-
-
- go (ExprStmt expr a_ty : stmts)
- = dsLExpr expr `thenDs` \ expr2 ->
- go stmts `thenDs` \ rest ->
- returnDs (mkApps then_id [Type a_ty, Type b_ty, expr2, rest])
-
- go (LetStmt binds : stmts)
- = go stmts `thenDs` \ rest ->
- dsLet binds rest
-
- go (BindStmt pat expr : stmts)
- = go stmts `thenDs` \ body ->
- dsLExpr expr `thenDs` \ rhs ->
- mkStringExpr (mk_msg (getLoc pat)) `thenDs` \ core_msg ->
- let
- -- In a do expression, pattern-match failure just calls
- -- the monadic 'fail' rather than throwing an exception
- fail_expr = mkApps fail_id [Type b_ty, core_msg]
- a_ty = hsPatType pat
- in
- selectSimpleMatchVarL pat `thenDs` \ var ->
- matchSimply (Var var) (StmtCtxt do_or_lc) pat
- body fail_expr `thenDs` \ match_code ->
- returnDs (mkApps bind_id [Type a_ty, Type b_ty, rhs, Lam var match_code])
-
- go (RecStmt rec_stmts later_vars rec_vars rec_rets : stmts)
- = go (bind_stmt : stmts)
- where
- bind_stmt = dsRecStmt m_ty ds_meths rec_stmts later_vars rec_vars rec_rets
-
- in
- go (map unLoc stmts) `thenDs` \ stmts_code ->
- returnDs (foldr Let stmts_code meth_binds)
-
+dsDo stmts body result_ty
+ = go (map unLoc stmts)
where
- mk_msg locn = "Pattern match failure in do expression at " ++ showSDoc (ppr locn)
+ go [] = dsLExpr body
+
+ go (ExprStmt rhs then_expr _ : stmts)
+ = do { rhs2 <- dsLExpr rhs
+ ; then_expr2 <- dsExpr then_expr
+ ; rest <- go stmts
+ ; returnDs (mkApps then_expr2 [rhs2, rest]) }
+
+ go (LetStmt binds : stmts)
+ = do { rest <- go stmts
+ ; dsLocalBinds binds rest }
+
+ go (BindStmt pat rhs bind_op fail_op : stmts)
+ = do { body <- go stmts
+ ; var <- selectSimpleMatchVarL pat
+ ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
+ result_ty (cantFailMatchResult body)
+ ; match_code <- handle_failure pat match fail_op
+ ; rhs' <- dsLExpr rhs
+ ; bind_op' <- dsExpr bind_op
+ ; returnDs (mkApps bind_op' [rhs', Lam var match_code]) }
+
+ -- In a do expression, pattern-match failure just calls
+ -- the monadic 'fail' rather than throwing an exception
+ handle_failure pat match fail_op
+ | matchCanFail match
+ = do { fail_op' <- dsExpr fail_op
+ ; fail_msg <- mkStringExpr (mk_fail_msg pat)
+ ; extractMatchResult match (App fail_op' fail_msg) }
+ | otherwise
+ = extractMatchResult match (error "It can't fail")
+
+mk_fail_msg pat = "Pattern match failure in do expression at " ++
+ showSDoc (ppr (getLoc pat))
\end{code}
Translation for RecStmt's:
return (v1,..vn))
\begin{code}
-dsRecStmt :: Type -- Monad type constructor :: * -> *
- -> [(Name,Id)] -- Rebound Ids
- -> [LStmt Id]
- -> [Id] -> [Id] -> [LHsExpr Id]
- -> Stmt Id
-dsRecStmt m_ty ds_meths stmts later_vars rec_vars rec_rets
- = ASSERT( length vars == length rets )
- BindStmt tup_pat mfix_app
- where
- vars@(var1:rest) = later_vars ++ rec_vars -- Always at least one
- rets@(ret1:_) = map nlHsVar later_vars ++ rec_rets
- one_var = null rest
+dsMDo :: PostTcTable
+ -> [LStmt Id]
+ -> LHsExpr Id
+ -> Type -- Type of the whole expression
+ -> DsM CoreExpr
+dsMDo tbl stmts body result_ty
+ = go (map unLoc stmts)
+ where
+ (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
+ mfix_id = lookupEvidence tbl mfixName
+ return_id = lookupEvidence tbl returnMName
+ bind_id = lookupEvidence tbl bindMName
+ then_id = lookupEvidence tbl thenMName
+ fail_id = lookupEvidence tbl failMName
+ ctxt = MDoExpr tbl
+
+ go [] = dsLExpr body
+
+ go (LetStmt binds : stmts)
+ = do { rest <- go stmts
+ ; dsLocalBinds binds rest }
+
+ go (ExprStmt rhs _ rhs_ty : stmts)
+ = do { rhs2 <- dsLExpr rhs
+ ; rest <- go stmts
+ ; returnDs (mkApps (Var then_id) [Type rhs_ty, Type b_ty, rhs2, rest]) }
+
+ go (BindStmt pat rhs _ _ : stmts)
+ = do { body <- go stmts
+ ; var <- selectSimpleMatchVarL pat
+ ; match <- matchSinglePat (Var var) (StmtCtxt ctxt) pat
+ result_ty (cantFailMatchResult body)
+ ; fail_msg <- mkStringExpr (mk_fail_msg pat)
+ ; let fail_expr = mkApps (Var fail_id) [Type b_ty, fail_msg]
+ ; match_code <- extractMatchResult match fail_expr
+
+ ; rhs' <- dsLExpr rhs
+ ; returnDs (mkApps (Var bind_id) [Type (hsPatType pat), Type b_ty,
+ rhs', Lam var match_code]) }
+
+ go (RecStmt rec_stmts later_ids rec_ids rec_rets binds : stmts)
+ = ASSERT( length rec_ids > 0 )
+ ASSERT( length rec_ids == length rec_rets )
+ go (new_bind_stmt : let_stmt : stmts)
+ where
+ new_bind_stmt = mkBindStmt (mk_tup_pat later_pats) mfix_app
+ let_stmt = LetStmt (HsValBinds (ValBindsOut [(Recursive, binds)] []))
+
+
+ -- Remove the later_ids that appear (without fancy coercions)
+ -- in rec_rets, because there's no need to knot-tie them separately
+ -- See Note [RecStmt] in HsExpr
+ later_ids' = filter (`notElem` mono_rec_ids) later_ids
+ mono_rec_ids = [ id | HsVar id <- rec_rets ]
+
mfix_app = nlHsApp (noLoc $ TyApp (nlHsVar mfix_id) [tup_ty]) mfix_arg
- mfix_arg = noLoc $ HsLam (MatchGroup [mkSimpleMatch [tup_pat] body]
+ mfix_arg = noLoc $ HsLam (MatchGroup [mkSimpleMatch [mfix_pat] body]
(mkFunTy tup_ty body_ty))
- tup_expr | one_var = ret1
- | otherwise = noLoc $ ExplicitTuple rets Boxed
- var_tys = map idType vars
- tup_ty = mkCoreTupTy var_tys -- Deals with singleton case
- tup_pat | one_var = nlVarPat var1
- | otherwise = noLoc $ LazyPat (noLoc $ TuplePat (map nlVarPat vars) Boxed)
+ -- The rec_tup_pat must bind the rec_ids only; remember that the
+ -- trimmed_laters may share the same Names
+ -- Meanwhile, the later_pats must bind the later_vars
+ rec_tup_pats = map mk_wild_pat later_ids' ++ map nlVarPat rec_ids
+ later_pats = map nlVarPat later_ids' ++ map mk_later_pat rec_ids
+ rets = map nlHsVar later_ids' ++ map noLoc rec_rets
- body = noLoc $ HsDo DoExpr (stmts ++ [return_stmt])
- [(n, HsVar id) | (n,id) <- ds_meths] -- A bit of a hack
- body_ty
+ mfix_pat = noLoc $ LazyPat $ mk_tup_pat rec_tup_pats
+ body = noLoc $ HsDo ctxt rec_stmts return_app body_ty
body_ty = mkAppTy m_ty tup_ty
+ tup_ty = mkCoreTupTy (map idType (later_ids' ++ rec_ids))
+ -- mkCoreTupTy deals with singleton case
+
+ return_app = nlHsApp (noLoc $ TyApp (nlHsVar return_id) [tup_ty])
+ (mk_ret_tup rets)
+
+ mk_wild_pat :: Id -> LPat Id
+ mk_wild_pat v = noLoc $ WildPat $ idType v
+
+ mk_later_pat :: Id -> LPat Id
+ mk_later_pat v | v `elem` later_ids' = mk_wild_pat v
+ | otherwise = nlVarPat v
- Var return_id = lookupReboundName ds_meths returnMName
- Var mfix_id = lookupReboundName ds_meths mfixName
+ mk_tup_pat :: [LPat Id] -> LPat Id
+ mk_tup_pat [p] = p
+ mk_tup_pat ps = noLoc $ mkVanillaTuplePat ps Boxed
- return_stmt = noLoc $ ResultStmt return_app
- return_app = nlHsApp (noLoc $ TyApp (nlHsVar return_id) [tup_ty]) tup_expr
+ mk_ret_tup :: [LHsExpr Id] -> LHsExpr Id
+ mk_ret_tup [r] = r
+ mk_ret_tup rs = noLoc $ ExplicitTuple rs Boxed
\end{code}