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Diffstat (limited to 'compiler/deSugar/DsUtils.lhs')
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diff --git a/compiler/deSugar/DsUtils.lhs b/compiler/deSugar/DsUtils.lhs new file mode 100644 index 0000000000..29e7773bb8 --- /dev/null +++ b/compiler/deSugar/DsUtils.lhs @@ -0,0 +1,884 @@ +% +% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 +% +\section[DsUtils]{Utilities for desugaring} + +This module exports some utility functions of no great interest. + +\begin{code} +module DsUtils ( + EquationInfo(..), + firstPat, shiftEqns, + + mkDsLet, mkDsLets, + + MatchResult(..), CanItFail(..), + cantFailMatchResult, alwaysFailMatchResult, + extractMatchResult, combineMatchResults, + adjustMatchResult, adjustMatchResultDs, + mkCoLetMatchResult, mkGuardedMatchResult, + matchCanFail, + mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult, + wrapBind, wrapBinds, + + mkErrorAppDs, mkNilExpr, mkConsExpr, mkListExpr, + mkIntExpr, mkCharExpr, + mkStringExpr, mkStringExprFS, mkIntegerExpr, + + mkSelectorBinds, mkTupleExpr, mkTupleSelector, + mkTupleType, mkTupleCase, mkBigCoreTup, + mkCoreTup, mkCoreTupTy, seqVar, + + dsSyntaxTable, lookupEvidence, + + selectSimpleMatchVarL, selectMatchVars, selectMatchVar + ) where + +#include "HsVersions.h" + +import {-# SOURCE #-} Match ( matchSimply ) +import {-# SOURCE #-} DsExpr( dsExpr ) + +import HsSyn +import TcHsSyn ( hsPatType ) +import CoreSyn +import Constants ( mAX_TUPLE_SIZE ) +import DsMonad + +import CoreUtils ( exprType, mkIfThenElse, mkCoerce, bindNonRec ) +import MkId ( iRREFUT_PAT_ERROR_ID, mkReboxingAlt, mkNewTypeBody ) +import Id ( idType, Id, mkWildId, mkTemplateLocals, mkSysLocal ) +import Var ( Var ) +import Name ( Name ) +import Literal ( Literal(..), mkStringLit, inIntRange, tARGET_MAX_INT ) +import TyCon ( isNewTyCon, tyConDataCons ) +import DataCon ( DataCon, dataConSourceArity, dataConTyCon, dataConTag ) +import Type ( mkFunTy, isUnLiftedType, Type, splitTyConApp, mkTyVarTy ) +import TcType ( tcEqType ) +import TysPrim ( intPrimTy ) +import TysWiredIn ( nilDataCon, consDataCon, + tupleCon, mkTupleTy, + unitDataConId, unitTy, + charTy, charDataCon, + intTy, intDataCon, + isPArrFakeCon ) +import BasicTypes ( Boxity(..) ) +import UniqSet ( mkUniqSet, minusUniqSet, isEmptyUniqSet ) +import UniqSupply ( splitUniqSupply, uniqFromSupply, uniqsFromSupply ) +import PrelNames ( unpackCStringName, unpackCStringUtf8Name, + plusIntegerName, timesIntegerName, smallIntegerDataConName, + lengthPName, indexPName ) +import Outputable +import SrcLoc ( Located(..), unLoc ) +import Util ( isSingleton, zipEqual, sortWith ) +import ListSetOps ( assocDefault ) +import FastString +import Data.Char ( ord ) + +#ifdef DEBUG +import Util ( notNull ) -- Used in an assertion +#endif +\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 + = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) -> + 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) + = dsExpr expr `thenDs` \ rhs -> + newSysLocalDs (exprType rhs) `thenDs` \ id -> + 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 + | isUnLiftedType (idType bndr) + = Case rhs bndr (exprType body) [(DEFAULT,[],body)] +mkDsLet bind body + = Let bind body + +mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr +mkDsLets binds body = foldr mkDsLet body binds +\end{code} + + +%************************************************************************ +%* * +\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) (hsPatType 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. +-- 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! + +selectMatchVars :: [Pat Id] -> [Type] -> DsM [Id] +selectMatchVars [] [] = return [] +selectMatchVars (p:ps) (ty:tys) = do { v <- selectMatchVar p ty + ; vs <- selectMatchVars ps tys + ; return (v:vs) } + +selectMatchVar (BangPat pat) pat_ty = selectMatchVar (unLoc pat) pat_ty +selectMatchVar (LazyPat pat) pat_ty = selectMatchVar (unLoc pat) pat_ty +selectMatchVar (VarPat var) pat_ty = try_for var pat_ty +selectMatchVar (AsPat var pat) pat_ty = try_for (unLoc var) pat_ty +selectMatchVar other_pat pat_ty = newSysLocalDs pat_ty -- OK, better make up one... + +try_for var pat_ty + | idType var `tcEqType` pat_ty = returnDs var + | otherwise = newSysLocalDs pat_ty +\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 = 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 -> returnDs fail) + +cantFailMatchResult :: CoreExpr -> MatchResult +cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr) + +extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr +extractMatchResult (MatchResult CantFail match_fn) fail_expr + = match_fn (error "It can't fail!") + +extractMatchResult (MatchResult CanFail match_fn) fail_expr + = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) -> + match_fn if_it_fails `thenDs` \ body -> + returnDs (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 = body_fn2 fail `thenDs` \ body2 -> + mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) -> + body_fn1 duplicatable_expr `thenDs` \ body1 -> + returnDs (Let fail_bind body1) + +combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2 + = match_result1 + +adjustMatchResult :: (CoreExpr -> CoreExpr) -> MatchResult -> MatchResult +adjustMatchResult encl_fn (MatchResult can_it_fail body_fn) + = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body -> + returnDs (encl_fn body)) + +adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult +adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn) + = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body -> + encl_fn body) + +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 match_result + = adjustMatchResult (mkDsLet bind) match_result + +mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult +mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn) + = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body -> + returnDs (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 + = mappM (mk_alt fail) sorted_alts `thenDs` \ alts -> + returnDs (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) = body_fn fail `thenDs` \ body -> + returnDs (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) = head match_alts + arg_id1 = head arg_ids1 + newtype_rhs = mkNewTypeBody tycon (idType arg_id1) (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 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts -> + returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts)) + + mk_alt fail (con, args, MatchResult _ body_fn) + = body_fn fail `thenDs` \ body -> + newUniqueSupply `thenDs` \ us -> + returnDs (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" + -- + mk_parrCase fail = + dsLookupGlobalId lengthPName `thenDs` \lengthP -> + unboxAlt `thenDs` \alt -> + returnDs (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 = + newSysLocalDs intPrimTy `thenDs` \l -> + dsLookupGlobalId indexPName `thenDs` \indexP -> + mappM (mkAlt indexP) sorted_alts `thenDs` \alts -> + returnDs (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) = + bodyFun fail `thenDs` \body -> + returnDs (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 + = getSrcSpanDs `thenDs` \ src_loc -> + let + full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg]) + core_msg = Lit (mkStringLit full_msg) + -- mkStringLit returns a result of type String# + in + returnDs (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 + = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc -> + returnDs (mkSmallIntegerLit integer_dc 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 -- Big, so start from a string + = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id -> + dsLookupGlobalId timesIntegerName `thenDs` \ times_id -> + dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc -> + let + lit i = mkSmallIntegerLit integer_dc 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 + + in + returnDs (horner tARGET_MAX_INT i) + +mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i] + +mkStringExpr str = mkStringExprFS (mkFastString str) + +mkStringExprFS str + | nullFS str + = returnDs (mkNilExpr charTy) + + | lengthFS str == 1 + = let + the_char = mkCharExpr (headFS str) + in + returnDs (mkConsExpr charTy the_char (mkNilExpr charTy)) + + | all safeChar chars + = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id -> + returnDs (App (Var unpack_id) (Lit (MachStr str))) + + | otherwise + = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id -> + returnDs (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 + = returnDs [(v, val_expr)] + +mkSelectorBinds pat val_expr + | isSingleton binders || is_simple_lpat pat + = -- 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. + newSysLocalDs (hsPatType pat) `thenDs` \ val_var -> + + -- 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 + mkErrorAppDs iRREFUT_PAT_ERROR_ID + unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr -> + newSysLocalDs unitTy `thenDs` \ err_var -> + mappM (mk_bind val_var err_var) binders `thenDs` \ binds -> + returnDs ( (val_var, val_expr) : + (err_var, err_expr) : + binds ) + + + | otherwise + = mkErrorAppDs iRREFUT_PAT_ERROR_ID + tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr -> + matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr -> + newSysLocalDs tuple_ty `thenDs` \ tuple_var -> + let + mk_tup_bind binder + = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var)) + in + returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders ) + where + binders = collectPatBinders pat + local_tuple = mkTupleExpr binders + tuple_ty = exprType local_tuple + + mk_bind scrut_var err_var bndr_var + -- (mk_bind sv err_var) generates + -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var } + -- Remember, pat binds bv + = matchSimply (Var scrut_var) PatBindRhs pat + (Var bndr_var) error_expr `thenDs` \ rhs_expr -> + returnDs (bndr_var, rhs_expr) + where + error_expr = mkCoerce (idType bndr_var) (Var err_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 _ _ _ _ ps _) = all is_triv_lpat (hsConArgs ps) + is_simple_pat (VarPat _) = True + is_simple_pat (ParPat p) = is_simple_lpat p + is_simple_pat other = False + + is_triv_lpat p = is_triv_pat (unLoc p) + + is_triv_pat (VarPat v) = True + is_triv_pat (WildPat _) = True + is_triv_pat (ParPat p) = is_triv_lpat p + is_triv_pat other = False +\end{code} + + +%************************************************************************ +%* * + Tuples +%* * +%************************************************************************ + +@mkTupleExpr@ 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. + +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} +mkTupleExpr :: [Id] -> CoreExpr +mkTupleExpr ids = mkBigCoreTup (map Var ids) + +-- corresponding type +mkTupleType :: [Id] -> Type +mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids) + +mkBigCoreTup :: [CoreExpr] -> CoreExpr +mkBigCoreTup = mkBigTuple mkCoreTup + +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} + + +@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 + mk_tuple_case us [vars] body + = mkSmallTupleCase vars body scrut_var scrut + 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 + + +-- The next three functions make tuple types, constructors and selectors, +-- with the rule that a 1-tuple is represented by the thing itselg +mkCoreTupTy :: [Type] -> Type +mkCoreTupTy [ty] = ty +mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys + +mkCoreTup :: [CoreExpr] -> CoreExpr +-- Builds exactly the specified tuple. +-- No fancy business for big tuples +mkCoreTup [] = Var unitDataConId +mkCoreTup [c] = c +mkCoreTup cs = mkConApp (tupleCon Boxed (length cs)) + (map (Type . exprType) cs ++ cs) + +mkCoreSel :: [Id] -- The tuple args + -> Id -- The selected one + -> Id -- A variable of the same type as the scrutinee + -> CoreExpr -- Scrutinee + -> CoreExpr +-- mkCoreSel [x,y,z] x v e +-- ===> case e of v { (x,y,z) -> x +mkCoreSel [var] should_be_the_same_var scrut_var scrut + = ASSERT(var == should_be_the_same_var) + scrut + +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 + = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var -> + newSysLocalDs unitTy `thenDs` \ fail_fun_arg -> + returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr), + App (Var fail_fun_var) (Var unitDataConId)) + + | otherwise + = newFailLocalDs ty `thenDs` \ fail_var -> + returnDs (NonRec fail_var expr, Var fail_var) + where + ty = exprType expr +\end{code} + + |