% % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % Utilities for desugaring This module exports some utility functions of no great interest. \begin{code} module DsUtils ( EquationInfo(..), firstPat, shiftEqns, mkDsLet, mkDsLets, mkDsApp, mkDsApps, MatchResult(..), CanItFail(..), cantFailMatchResult, alwaysFailMatchResult, extractMatchResult, combineMatchResults, adjustMatchResult, adjustMatchResultDs, mkCoLetMatchResult, mkViewMatchResult, mkGuardedMatchResult, matchCanFail, mkEvalMatchResult, mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult, wrapBind, wrapBinds, mkErrorAppDs, mkNilExpr, mkConsExpr, mkListExpr, mkIntExpr, mkCharExpr, mkStringExpr, mkStringExprFS, mkIntegerExpr, mkBuildExpr, mkFoldrExpr, seqVar, -- Core tuples mkCoreVarTup, mkCoreTup, mkCoreVarTupTy, mkCoreTupTy, mkBigCoreVarTup, mkBigCoreTup, mkBigCoreVarTupTy, mkBigCoreTupTy, -- LHs tuples mkLHsVarTup, mkLHsTup, mkLHsVarPatTup, mkLHsPatTup, mkBigLHsVarTup, mkBigLHsTup, mkBigLHsVarPatTup, mkBigLHsPatTup, -- Tuple bindings mkSelectorBinds, mkTupleSelector, mkSmallTupleCase, mkTupleCase, dsSyntaxTable, lookupEvidence, selectSimpleMatchVarL, selectMatchVars, selectMatchVar, mkTickBox, mkOptTickBox, mkBinaryTickBox ) where #include "HsVersions.h" import {-# SOURCE #-} Match ( matchSimply ) import {-# SOURCE #-} DsExpr( dsExpr ) import HsSyn import TcHsSyn import CoreSyn import Constants import DsMonad import CoreUtils import MkId import Id import Var import Name import Literal import TyCon import DataCon import Type import Coercion import TysPrim import TysWiredIn import BasicTypes import UniqSet import UniqSupply import PrelNames import Outputable import SrcLoc import Util import ListSetOps import FastString import StaticFlags import Data.Char infixl 4 `mkDsApp`, `mkDsApps` \end{code} %************************************************************************ %* * Rebindable syntax %* * %************************************************************************ \begin{code} dsSyntaxTable :: SyntaxTable Id -> DsM ([CoreBind], -- Auxiliary bindings [(Name,Id)]) -- Maps the standard name to its value dsSyntaxTable rebound_ids = do (binds_s, prs) <- mapAndUnzipM mk_bind rebound_ids return (concat binds_s, prs) where -- The cheapo special case can happen when we -- make an intermediate HsDo when desugaring a RecStmt mk_bind (std_name, HsVar id) = return ([], (std_name, id)) mk_bind (std_name, expr) = do rhs <- dsExpr expr id <- newSysLocalDs (exprType rhs) return ([NonRec id rhs], (std_name, id)) lookupEvidence :: [(Name, Id)] -> Name -> Id lookupEvidence prs std_name = assocDefault (mk_panic std_name) prs std_name where mk_panic std_name = pprPanic "dsSyntaxTable" (ptext (sLit "Not found:") <+> ppr std_name) \end{code} %************************************************************************ %* * \subsection{Building lets} %* * %************************************************************************ Use case, not let for unlifted types. The simplifier will turn some back again. \begin{code} mkDsLet :: CoreBind -> CoreExpr -> CoreExpr mkDsLet (NonRec bndr rhs) body -- See Note [CoreSyn let/app invariant] | isUnLiftedType (idType bndr) && not (exprOkForSpeculation rhs) = Case rhs bndr (exprType body) [(DEFAULT,[],body)] mkDsLet bind body = Let bind body mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr mkDsLets binds body = foldr mkDsLet body binds ----------- mkDsApp :: CoreExpr -> CoreExpr -> CoreExpr -- Check the invariant that the arg of an App is ok-for-speculation if unlifted -- See CoreSyn Note [CoreSyn let/app invariant] mkDsApp fun (Type ty) = App fun (Type ty) mkDsApp fun arg = mk_val_app fun arg arg_ty res_ty where (arg_ty, res_ty) = splitFunTy (exprType fun) ----------- mkDsApps :: CoreExpr -> [CoreExpr] -> CoreExpr -- Slightly more efficient version of (foldl mkDsApp) mkDsApps fun args = go fun (exprType fun) args where go fun _ [] = fun go fun fun_ty (Type ty : args) = go (App fun (Type ty)) (applyTy fun_ty ty) args go fun fun_ty (arg : args) = go (mk_val_app fun arg arg_ty res_ty) res_ty args where (arg_ty, res_ty) = splitFunTy fun_ty ----------- mk_val_app :: CoreExpr -> CoreExpr -> Type -> Type -> CoreExpr mk_val_app (Var f `App` Type ty1 `App` Type _ `App` arg1) arg2 _ res_ty | f == seqId -- Note [Desugaring seq (1), (2)] = Case arg1 case_bndr res_ty [(DEFAULT,[],arg2)] where case_bndr = case arg1 of Var v1 -> v1 -- Note [Desugaring seq (2)] _ -> mkWildId ty1 mk_val_app fun arg arg_ty _ -- See Note [CoreSyn let/app invariant] | not (isUnLiftedType arg_ty) || exprOkForSpeculation arg = App fun arg -- The vastly common case mk_val_app fun arg arg_ty res_ty = Case arg (mkWildId arg_ty) res_ty [(DEFAULT,[],App fun (Var arg_id))] where arg_id = mkWildId arg_ty -- Lots of shadowing, but it doesn't matter, -- because 'fun ' should not have a free wild-id \end{code} Note [Desugaring seq (1)] cf Trac #1031 ~~~~~~~~~~~~~~~~~~~~~~~~~ f x y = x `seq` (y `seq` (# x,y #)) The [CoreSyn let/app invariant] means that, other things being equal, because the argument to the outer 'seq' has an unlifted type, we'll use call-by-value thus: f x y = case (y `seq` (# x,y #)) of v -> x `seq` v But that is bad for two reasons: (a) we now evaluate y before x, and (b) we can't bind v to an unboxed pair Seq is very, very special! So we recognise it right here, and desugar to case x of _ -> case y of _ -> (# x,y #) Note [Desugaring seq (2)] cf Trac #2231 ~~~~~~~~~~~~~~~~~~~~~~~~~ Consider let chp = case b of { True -> fst x; False -> 0 } in chp `seq` ...chp... Here the seq is designed to plug the space leak of retaining (snd x) for too long. If we rely on the ordinary inlining of seq, we'll get let chp = case b of { True -> fst x; False -> 0 } case chp of _ { I# -> ...chp... } But since chp is cheap, and the case is an alluring contet, we'll inline chp into the case scrutinee. Now there is only one use of chp, so we'll inline a second copy. Alas, we've now ruined the purpose of the seq, by re-introducing the space leak: case (case b of {True -> fst x; False -> 0}) of I# _ -> ...case b of {True -> fst x; False -> 0}... We can try to avoid doing this by ensuring that the binder-swap in the case happens, so we get his at an early stage: case chp of chp2 { I# -> ...chp2... } But this is fragile. The real culprit is the source program. Perhpas we should have said explicitly let !chp2 = chp in ...chp2... But that's painful. So the code here does a little hack to make seq more robust: a saturated application of 'seq' is turned *directly* into the case expression. So we desugar to: let chp = case b of { True -> fst x; False -> 0 } case chp of chp { I# -> ...chp... } Notice the shadowing of the case binder! And now all is well. The reason it's a hack is because if you define mySeq=seq, the hack won't work on mySeq. %************************************************************************ %* * \subsection{ Selecting match variables} %* * %************************************************************************ We're about to match against some patterns. We want to make some @Ids@ to use as match variables. If a pattern has an @Id@ readily at hand, which should indeed be bound to the pattern as a whole, then use it; otherwise, make one up. \begin{code} selectSimpleMatchVarL :: LPat Id -> DsM Id selectSimpleMatchVarL pat = selectMatchVar (unLoc pat) -- (selectMatchVars ps tys) chooses variables of type tys -- to use for matching ps against. If the pattern is a variable, -- we try to use that, to save inventing lots of fresh variables. -- -- OLD, but interesting note: -- But even if it is a variable, its type might not match. Consider -- data T a where -- T1 :: Int -> T Int -- T2 :: a -> T a -- -- f :: T a -> a -> Int -- f (T1 i) (x::Int) = x -- f (T2 i) (y::a) = 0 -- Then we must not choose (x::Int) as the matching variable! -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat selectMatchVars :: [Pat Id] -> DsM [Id] selectMatchVars ps = mapM selectMatchVar ps selectMatchVar :: Pat Id -> DsM Id selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat) selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat) selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat) selectMatchVar (VarPat var) = return var selectMatchVar (AsPat var _) = return (unLoc var) selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat) -- OK, better make up one... \end{code} %************************************************************************ %* * %* type synonym EquationInfo and access functions for its pieces * %* * %************************************************************************ \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym} The ``equation info'' used by @match@ is relatively complicated and worthy of a type synonym and a few handy functions. \begin{code} firstPat :: EquationInfo -> Pat Id firstPat eqn = ASSERT( notNull (eqn_pats eqn) ) head (eqn_pats eqn) shiftEqns :: [EquationInfo] -> [EquationInfo] -- Drop the first pattern in each equation shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ] \end{code} Functions on MatchResults \begin{code} matchCanFail :: MatchResult -> Bool matchCanFail (MatchResult CanFail _) = True matchCanFail (MatchResult CantFail _) = False alwaysFailMatchResult :: MatchResult alwaysFailMatchResult = MatchResult CanFail (\fail -> return fail) cantFailMatchResult :: CoreExpr -> MatchResult cantFailMatchResult expr = MatchResult CantFail (\_ -> return expr) extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr extractMatchResult (MatchResult CantFail match_fn) _ = match_fn (error "It can't fail!") extractMatchResult (MatchResult CanFail match_fn) fail_expr = do (fail_bind, if_it_fails) <- mkFailurePair fail_expr body <- match_fn if_it_fails return (mkDsLet fail_bind body) combineMatchResults :: MatchResult -> MatchResult -> MatchResult combineMatchResults (MatchResult CanFail body_fn1) (MatchResult can_it_fail2 body_fn2) = MatchResult can_it_fail2 body_fn where body_fn fail = do body2 <- body_fn2 fail (fail_bind, duplicatable_expr) <- mkFailurePair body2 body1 <- body_fn1 duplicatable_expr return (Let fail_bind body1) combineMatchResults match_result1@(MatchResult CantFail _) _ = match_result1 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult adjustMatchResult encl_fn (MatchResult can_it_fail body_fn) = MatchResult can_it_fail (\fail -> encl_fn <$> body_fn fail) adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn) = MatchResult can_it_fail (\fail -> encl_fn =<< body_fn fail) wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr wrapBinds [] e = e wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e) wrapBind :: Var -> Var -> CoreExpr -> CoreExpr wrapBind new old body | new==old = body | isTyVar new = App (Lam new body) (Type (mkTyVarTy old)) | otherwise = Let (NonRec new (Var old)) body seqVar :: Var -> CoreExpr -> CoreExpr seqVar var body = Case (Var var) var (exprType body) [(DEFAULT, [], body)] mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind) -- (mkViewMatchResult var' viewExpr var mr) makes the expression -- let var' = viewExpr var in mr mkViewMatchResult :: Id -> CoreExpr -> Id -> MatchResult -> MatchResult mkViewMatchResult var' viewExpr var = adjustMatchResult (mkDsLet (NonRec var' (mkDsApp viewExpr (Var var)))) mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult mkEvalMatchResult var ty = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)]) mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult mkGuardedMatchResult pred_expr (MatchResult _ body_fn) = MatchResult CanFail (\fail -> do body <- body_fn fail return (mkIfThenElse pred_expr body fail)) mkCoPrimCaseMatchResult :: Id -- Scrutinee -> Type -- Type of the case -> [(Literal, MatchResult)] -- Alternatives -> MatchResult mkCoPrimCaseMatchResult var ty match_alts = MatchResult CanFail mk_case where mk_case fail = do alts <- mapM (mk_alt fail) sorted_alts return (Case (Var var) var ty ((DEFAULT, [], fail) : alts)) sorted_alts = sortWith fst match_alts -- Right order for a Case mk_alt fail (lit, MatchResult _ body_fn) = do body <- body_fn fail return (LitAlt lit, [], body) mkCoAlgCaseMatchResult :: Id -- Scrutinee -> Type -- Type of exp -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives -> MatchResult mkCoAlgCaseMatchResult var ty match_alts | isNewTyCon tycon -- Newtype case; use a let = ASSERT( null (tail match_alts) && null (tail arg_ids1) ) mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case = MatchResult CanFail mk_parrCase | otherwise -- Datatype case; use a case = MatchResult fail_flag mk_case where tycon = dataConTyCon con1 -- [Interesting: becuase of GADTs, we can't rely on the type of -- the scrutinised Id to be sufficiently refined to have a TyCon in it] -- Stuff for newtype (con1, arg_ids1, match_result1) = ASSERT( notNull match_alts ) head match_alts arg_id1 = ASSERT( notNull arg_ids1 ) head arg_ids1 var_ty = idType var (tc, ty_args) = splitNewTyConApp var_ty newtype_rhs = unwrapNewTypeBody tc ty_args (Var var) -- Stuff for data types data_cons = tyConDataCons tycon match_results = [match_result | (_,_,match_result) <- match_alts] fail_flag | exhaustive_case = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results] | otherwise = CanFail wild_var = mkWildId (idType var) sorted_alts = sortWith get_tag match_alts get_tag (con, _, _) = dataConTag con mk_case fail = do alts <- mapM (mk_alt fail) sorted_alts return (Case (Var var) wild_var ty (mk_default fail ++ alts)) mk_alt fail (con, args, MatchResult _ body_fn) = do body <- body_fn fail us <- newUniqueSupply return (mkReboxingAlt (uniqsFromSupply us) con args body) mk_default fail | exhaustive_case = [] | otherwise = [(DEFAULT, [], fail)] un_mentioned_constructors = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts] exhaustive_case = isEmptyUniqSet un_mentioned_constructors -- Stuff for parallel arrays -- -- * the following is to desugar cases over fake constructors for -- parallel arrays, which are introduced by `tidy1' in the `PArrPat' -- case -- -- Concerning `isPArrFakeAlts': -- -- * it is *not* sufficient to just check the type of the type -- constructor, as we have to be careful not to confuse the real -- representation of parallel arrays with the fake constructors; -- moreover, a list of alternatives must not mix fake and real -- constructors (this is checked earlier on) -- -- FIXME: We actually go through the whole list and make sure that -- either all or none of the constructors are fake parallel -- array constructors. This is to spot equations that mix fake -- constructors with the real representation defined in -- `PrelPArr'. It would be nicer to spot this situation -- earlier and raise a proper error message, but it can really -- only happen in `PrelPArr' anyway. -- isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon isPArrFakeAlts ((dcon, _, _):alts) = case (isPArrFakeCon dcon, isPArrFakeAlts alts) of (True , True ) -> True (False, False) -> False _ -> panic "DsUtils: you may not mix `[:...:]' with `PArr' patterns" isPArrFakeAlts [] = panic "DsUtils: unexpectedly found an empty list of PArr fake alternatives" -- mk_parrCase fail = do lengthP <- dsLookupGlobalId lengthPName alt <- unboxAlt return (Case (len lengthP) (mkWildId intTy) ty [alt]) where elemTy = case splitTyConApp (idType var) of (_, [elemTy]) -> elemTy _ -> panic panicMsg panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?" len lengthP = mkApps (Var lengthP) [Type elemTy, Var var] -- unboxAlt = do l <- newSysLocalDs intPrimTy indexP <- dsLookupGlobalId indexPName alts <- mapM (mkAlt indexP) sorted_alts return (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts))) where wild = mkWildId intPrimTy dft = (DEFAULT, [], fail) -- -- each alternative matches one array length (corresponding to one -- fake array constructor), so the match is on a literal; each -- alternative's body is extended by a local binding for each -- constructor argument, which are bound to array elements starting -- with the first -- mkAlt indexP (con, args, MatchResult _ bodyFun) = do body <- bodyFun fail return (LitAlt lit, [], mkDsLets binds body) where lit = MachInt $ toInteger (dataConSourceArity con) binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args] -- indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i] \end{code} %************************************************************************ %* * \subsection{Desugarer's versions of some Core functions} %* * %************************************************************************ \begin{code} mkErrorAppDs :: Id -- The error function -> Type -- Type to which it should be applied -> String -- The error message string to pass -> DsM CoreExpr mkErrorAppDs err_id ty msg = do src_loc <- getSrcSpanDs let full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg]) core_msg = Lit (mkStringLit full_msg) -- mkStringLit returns a result of type String# return (mkApps (Var err_id) [Type ty, core_msg]) \end{code} ************************************************************* %* * \subsection{Making literals} %* * %************************************************************************ \begin{code} mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer mkStringExpr :: String -> DsM CoreExpr -- Result :: String mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String mkIntExpr i = mkConApp intDataCon [mkIntLit i] mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)] mkIntegerExpr i | inIntRange i -- Small enough, so start from an Int = do integer_id <- dsLookupGlobalId smallIntegerName return (mkSmallIntegerLit integer_id i) -- Special case for integral literals with a large magnitude: -- They are transformed into an expression involving only smaller -- integral literals. This improves constant folding. | otherwise = do -- Big, so start from a string plus_id <- dsLookupGlobalId plusIntegerName times_id <- dsLookupGlobalId timesIntegerName integer_id <- dsLookupGlobalId smallIntegerName let lit i = mkSmallIntegerLit integer_id i plus a b = Var plus_id `App` a `App` b times a b = Var times_id `App` a `App` b -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b horner :: Integer -> Integer -> CoreExpr horner b i | abs q <= 1 = if r == 0 || r == i then lit i else lit r `plus` lit (i-r) | r == 0 = horner b q `times` lit b | otherwise = lit r `plus` (horner b q `times` lit b) where (q,r) = i `quotRem` b return (horner tARGET_MAX_INT i) mkSmallIntegerLit :: Id -> Integer -> CoreExpr mkSmallIntegerLit small_integer i = mkApps (Var small_integer) [mkIntLit i] mkStringExpr str = mkStringExprFS (mkFastString str) mkStringExprFS str | nullFS str = return (mkNilExpr charTy) | lengthFS str == 1 = do let the_char = mkCharExpr (headFS str) return (mkConsExpr charTy the_char (mkNilExpr charTy)) | all safeChar chars = do unpack_id <- dsLookupGlobalId unpackCStringName return (App (Var unpack_id) (Lit (MachStr str))) | otherwise = do unpack_id <- dsLookupGlobalId unpackCStringUtf8Name return (App (Var unpack_id) (Lit (MachStr str))) where chars = unpackFS str safeChar c = ord c >= 1 && ord c <= 0x7F \end{code} %************************************************************************ %* * \subsection[mkSelectorBind]{Make a selector bind} %* * %************************************************************************ This is used in various places to do with lazy patterns. For each binder $b$ in the pattern, we create a binding: \begin{verbatim} b = case v of pat' -> b' \end{verbatim} where @pat'@ is @pat@ with each binder @b@ cloned into @b'@. ToDo: making these bindings should really depend on whether there's much work to be done per binding. If the pattern is complex, it should be de-mangled once, into a tuple (and then selected from). Otherwise the demangling can be in-line in the bindings (as here). Boring! Boring! One error message per binder. The above ToDo is even more helpful. Something very similar happens for pattern-bound expressions. \begin{code} mkSelectorBinds :: LPat Id -- The pattern -> CoreExpr -- Expression to which the pattern is bound -> DsM [(Id,CoreExpr)] mkSelectorBinds (L _ (VarPat v)) val_expr = return [(v, val_expr)] mkSelectorBinds pat val_expr | isSingleton binders || is_simple_lpat pat = do -- Given p = e, where p binds x,y -- we are going to make -- v = p (where v is fresh) -- x = case v of p -> x -- y = case v of p -> x -- Make up 'v' -- NB: give it the type of *pattern* p, not the type of the *rhs* e. -- This does not matter after desugaring, but there's a subtle -- issue with implicit parameters. Consider -- (x,y) = ?i -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque -- to the desugarer. (Why opaque? Because newtypes have to be. Why -- does it get that type? So that when we abstract over it we get the -- right top-level type (?i::Int) => ...) -- -- So to get the type of 'v', use the pattern not the rhs. Often more -- efficient too. val_var <- newSysLocalDs (hsLPatType pat) -- For the error message we make one error-app, to avoid duplication. -- But we need it at different types... so we use coerce for that err_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID unitTy (showSDoc (ppr pat)) err_var <- newSysLocalDs unitTy binds <- mapM (mk_bind val_var err_var) binders return ( (val_var, val_expr) : (err_var, err_expr) : binds ) | otherwise = do error_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID tuple_ty (showSDoc (ppr pat)) tuple_expr <- matchSimply val_expr PatBindRhs pat local_tuple error_expr tuple_var <- newSysLocalDs tuple_ty let mk_tup_bind binder = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var)) return ( (tuple_var, tuple_expr) : map mk_tup_bind binders ) where binders = collectPatBinders pat local_tuple = mkBigCoreVarTup binders tuple_ty = exprType local_tuple mk_bind scrut_var err_var bndr_var = do -- (mk_bind sv err_var) generates -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var } -- Remember, pat binds bv rhs_expr <- matchSimply (Var scrut_var) PatBindRhs pat (Var bndr_var) error_expr return (bndr_var, rhs_expr) where error_expr = mkCoerce co (Var err_var) co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var) is_simple_lpat p = is_simple_pat (unLoc p) is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConPatArgs ps) is_simple_pat (VarPat _) = True is_simple_pat (ParPat p) = is_simple_lpat p is_simple_pat _ = False is_triv_lpat p = is_triv_pat (unLoc p) is_triv_pat (VarPat _) = True is_triv_pat (WildPat _) = True is_triv_pat (ParPat p) = is_triv_lpat p is_triv_pat _ = False \end{code} %************************************************************************ %* * Big Tuples %* * %************************************************************************ Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big. \begin{code} mkBigTuple :: ([a] -> a) -> [a] -> a mkBigTuple small_tuple as = mk_big_tuple (chunkify as) where -- Each sub-list is short enough to fit in a tuple mk_big_tuple [as] = small_tuple as mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s)) chunkify :: [a] -> [[a]] -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE -- But there may be more than mAX_TUPLE_SIZE sub-lists chunkify xs | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs] | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs) where n_xs = length xs split [] = [] split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs) \end{code} Creating tuples and their types for Core expressions @mkBigCoreVarTup@ builds a tuple; the inverse to @mkTupleSelector@. * If it has only one element, it is the identity function. * If there are more elements than a big tuple can have, it nests the tuples. \begin{code} -- Small tuples: build exactly the specified tuple mkCoreVarTup :: [Id] -> CoreExpr mkCoreVarTup ids = mkCoreTup (map Var ids) mkCoreVarTupTy :: [Id] -> Type mkCoreVarTupTy ids = mkCoreTupTy (map idType ids) mkCoreTup :: [CoreExpr] -> CoreExpr mkCoreTup [] = Var unitDataConId mkCoreTup [c] = c mkCoreTup cs = mkConApp (tupleCon Boxed (length cs)) (map (Type . exprType) cs ++ cs) mkCoreTupTy :: [Type] -> Type mkCoreTupTy [ty] = ty mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys -- Big tuples mkBigCoreVarTup :: [Id] -> CoreExpr mkBigCoreVarTup ids = mkBigCoreTup (map Var ids) mkBigCoreVarTupTy :: [Id] -> Type mkBigCoreVarTupTy ids = mkBigCoreTupTy (map idType ids) mkBigCoreTup :: [CoreExpr] -> CoreExpr mkBigCoreTup = mkBigTuple mkCoreTup mkBigCoreTupTy :: [Type] -> Type mkBigCoreTupTy = mkBigTuple mkCoreTupTy \end{code} Creating tuples and their types for full Haskell expressions \begin{code} -- Smart constructors for source tuple expressions mkLHsVarTup :: [Id] -> LHsExpr Id mkLHsVarTup ids = mkLHsTup (map nlHsVar ids) mkLHsTup :: [LHsExpr Id] -> LHsExpr Id mkLHsTup [] = nlHsVar unitDataConId mkLHsTup [lexp] = lexp mkLHsTup lexps = noLoc $ ExplicitTuple lexps Boxed -- Smart constructors for source tuple patterns mkLHsVarPatTup :: [Id] -> LPat Id mkLHsVarPatTup bs = mkLHsPatTup (map nlVarPat bs) mkLHsPatTup :: [LPat Id] -> LPat Id mkLHsPatTup [lpat] = lpat mkLHsPatTup lpats = noLoc $ mkVanillaTuplePat lpats Boxed -- Handles the case where lpats = [] gracefully -- The Big equivalents for the source tuple expressions mkBigLHsVarTup :: [Id] -> LHsExpr Id mkBigLHsVarTup ids = mkBigLHsTup (map nlHsVar ids) mkBigLHsTup :: [LHsExpr Id] -> LHsExpr Id mkBigLHsTup = mkBigTuple mkLHsTup -- The Big equivalents for the source tuple patterns mkBigLHsVarPatTup :: [Id] -> LPat Id mkBigLHsVarPatTup bs = mkBigLHsPatTup (map nlVarPat bs) mkBigLHsPatTup :: [LPat Id] -> LPat Id mkBigLHsPatTup = mkBigTuple mkLHsPatTup \end{code} @mkTupleSelector@ builds a selector which scrutises the given expression and extracts the one name from the list given. If you want the no-shadowing rule to apply, the caller is responsible for making sure that none of these names are in scope. If there is just one id in the ``tuple'', then the selector is just the identity. If it's big, it does nesting mkTupleSelector [a,b,c,d] b v e = case e of v { (p,q) -> case p of p { (a,b) -> b }} We use 'tpl' vars for the p,q, since shadowing does not matter. In fact, it's more convenient to generate it innermost first, getting case (case e of v (p,q) -> p) of p (a,b) -> b \begin{code} mkTupleSelector :: [Id] -- The tuple args -> Id -- The selected one -> Id -- A variable of the same type as the scrutinee -> CoreExpr -- Scrutinee -> CoreExpr mkTupleSelector vars the_var scrut_var scrut = mk_tup_sel (chunkify vars) the_var where mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $ mk_tup_sel (chunkify tpl_vs) tpl_v where tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s] tpl_vs = mkTemplateLocals tpl_tys [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s, the_var `elem` gp ] \end{code} A generalization of @mkTupleSelector@, allowing the body of the case to be an arbitrary expression. If the tuple is big, it is nested: mkTupleCase uniqs [a,b,c,d] body v e = case e of v { (p,q) -> case p of p { (a,b) -> case q of q { (c,d) -> body }}} To avoid shadowing, we use uniqs to invent new variables p,q. ToDo: eliminate cases where none of the variables are needed. \begin{code} mkTupleCase :: UniqSupply -- for inventing names of intermediate variables -> [Id] -- the tuple args -> CoreExpr -- body of the case -> Id -- a variable of the same type as the scrutinee -> CoreExpr -- scrutinee -> CoreExpr mkTupleCase uniqs vars body scrut_var scrut = mk_tuple_case uniqs (chunkify vars) body where -- This is the case where don't need any nesting mk_tuple_case _ [vars] body = mkSmallTupleCase vars body scrut_var scrut -- This is the case where we must make nest tuples at least once mk_tuple_case us vars_s body = let (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s in mk_tuple_case us' (chunkify vars') body' one_tuple_case chunk_vars (us, vs, body) = let (us1, us2) = splitUniqSupply us scrut_var = mkSysLocal (fsLit "ds") (uniqFromSupply us1) (mkCoreTupTy (map idType chunk_vars)) body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var) in (us2, scrut_var:vs, body') \end{code} The same, but with a tuple small enough not to need nesting. \begin{code} mkSmallTupleCase :: [Id] -- the tuple args -> CoreExpr -- body of the case -> Id -- a variable of the same type as the scrutinee -> CoreExpr -- scrutinee -> CoreExpr mkSmallTupleCase [var] body _scrut_var scrut = bindNonRec var scrut body mkSmallTupleCase vars body scrut_var scrut -- One branch no refinement? = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)] \end{code} %************************************************************************ %* * \subsection[mkFailurePair]{Code for pattern-matching and other failures} %* * %************************************************************************ Call the constructor Ids when building explicit lists, so that they interact well with rules. \begin{code} mkNilExpr :: Type -> CoreExpr mkNilExpr ty = mkConApp nilDataCon [Type ty] mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl] mkListExpr :: Type -> [CoreExpr] -> CoreExpr mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs mkFoldrExpr :: PostTcType -> PostTcType -> CoreExpr -> CoreExpr -> CoreExpr -> DsM CoreExpr mkFoldrExpr elt_ty result_ty c n list = do foldr_id <- dsLookupGlobalId foldrName return (Var foldr_id `App` Type elt_ty `App` Type result_ty `App` c `App` n `App` list) mkBuildExpr :: Type -> ((Id, Type) -> (Id, Type) -> DsM CoreExpr) -> DsM CoreExpr mkBuildExpr elt_ty mk_build_inside = do [n_tyvar] <- newTyVarsDs [alphaTyVar] let n_ty = mkTyVarTy n_tyvar c_ty = mkFunTys [elt_ty, n_ty] n_ty [c, n] <- newSysLocalsDs [c_ty, n_ty] build_inside <- mk_build_inside (c, c_ty) (n, n_ty) build_id <- dsLookupGlobalId buildName return $ Var build_id `App` Type elt_ty `App` mkLams [n_tyvar, c, n] build_inside mkCoreSel :: [Id] -- The tuple args -> Id -- The selected one -> Id -- A variable of the same type as the scrutinee -> CoreExpr -- Scrutinee -> CoreExpr -- mkCoreSel [x] x v e -- ===> e mkCoreSel [var] should_be_the_same_var _ scrut = ASSERT(var == should_be_the_same_var) scrut -- mkCoreSel [x,y,z] x v e -- ===> case e of v { (x,y,z) -> x mkCoreSel vars the_var scrut_var scrut = ASSERT( notNull vars ) Case scrut scrut_var (idType the_var) [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)] \end{code} %************************************************************************ %* * \subsection[mkFailurePair]{Code for pattern-matching and other failures} %* * %************************************************************************ Generally, we handle pattern matching failure like this: let-bind a fail-variable, and use that variable if the thing fails: \begin{verbatim} let fail.33 = error "Help" in case x of p1 -> ... p2 -> fail.33 p3 -> fail.33 p4 -> ... \end{verbatim} Then \begin{itemize} \item If the case can't fail, then there'll be no mention of @fail.33@, and the simplifier will later discard it. \item If it can fail in only one way, then the simplifier will inline it. \item Only if it is used more than once will the let-binding remain. \end{itemize} There's a problem when the result of the case expression is of unboxed type. Then the type of @fail.33@ is unboxed too, and there is every chance that someone will change the let into a case: \begin{verbatim} case error "Help" of fail.33 -> case .... \end{verbatim} which is of course utterly wrong. Rather than drop the condition that only boxed types can be let-bound, we just turn the fail into a function for the primitive case: \begin{verbatim} let fail.33 :: Void -> Int# fail.33 = \_ -> error "Help" in case x of p1 -> ... p2 -> fail.33 void p3 -> fail.33 void p4 -> ... \end{verbatim} Now @fail.33@ is a function, so it can be let-bound. \begin{code} mkFailurePair :: CoreExpr -- Result type of the whole case expression -> DsM (CoreBind, -- Binds the newly-created fail variable -- to either the expression or \ _ -> expression CoreExpr) -- Either the fail variable, or fail variable -- applied to unit tuple mkFailurePair expr | isUnLiftedType ty = do fail_fun_var <- newFailLocalDs (unitTy `mkFunTy` ty) fail_fun_arg <- newSysLocalDs unitTy return (NonRec fail_fun_var (Lam fail_fun_arg expr), App (Var fail_fun_var) (Var unitDataConId)) | otherwise = do fail_var <- newFailLocalDs ty return (NonRec fail_var expr, Var fail_var) where ty = exprType expr \end{code} \begin{code} mkOptTickBox :: Maybe (Int,[Id]) -> CoreExpr -> DsM CoreExpr mkOptTickBox Nothing e = return e mkOptTickBox (Just (ix,ids)) e = mkTickBox ix ids e mkTickBox :: Int -> [Id] -> CoreExpr -> DsM CoreExpr mkTickBox ix vars e = do uq <- newUnique mod <- getModuleDs let tick | opt_Hpc = mkTickBoxOpId uq mod ix | otherwise = mkBreakPointOpId uq mod ix uq2 <- newUnique let occName = mkVarOcc "tick" let name = mkInternalName uq2 occName noSrcSpan -- use mkSysLocal? let var = Id.mkLocalId name realWorldStatePrimTy scrut <- if opt_Hpc then return (Var tick) else do let tickVar = Var tick let tickType = mkFunTys (map idType vars) realWorldStatePrimTy let scrutApTy = App tickVar (Type tickType) return (mkApps scrutApTy (map Var vars) :: Expr Id) return $ Case scrut var ty [(DEFAULT,[],e)] where ty = exprType e mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr mkBinaryTickBox ixT ixF e = do uq <- newUnique let bndr1 = mkSysLocal (fsLit "t1") uq boolTy falseBox <- mkTickBox ixF [] $ Var falseDataConId trueBox <- mkTickBox ixT [] $ Var trueDataConId return $ Case e bndr1 boolTy [ (DataAlt falseDataCon, [], falseBox) , (DataAlt trueDataCon, [], trueBox) ] \end{code}