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Diffstat (limited to 'compiler/deSugar/DsExpr.lhs')
| -rw-r--r-- | compiler/deSugar/DsExpr.lhs | 781 |
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diff --git a/compiler/deSugar/DsExpr.lhs b/compiler/deSugar/DsExpr.lhs new file mode 100644 index 0000000000..e8e9e7b370 --- /dev/null +++ b/compiler/deSugar/DsExpr.lhs @@ -0,0 +1,781 @@ +% +% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 +% +\section[DsExpr]{Matching expressions (Exprs)} + +\begin{code} +module DsExpr ( dsExpr, dsLExpr, dsLocalBinds, dsValBinds, dsLit ) where + +#include "HsVersions.h" +#if defined(GHCI) && defined(BREAKPOINT) +import Foreign.StablePtr ( newStablePtr, castStablePtrToPtr ) +import GHC.Exts ( Ptr(..), Int(..), addr2Int# ) +import IOEnv ( ioToIOEnv ) +import PrelNames ( breakpointJumpName ) +import TysWiredIn ( unitTy ) +import TypeRep ( Type(..) ) +#endif + +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, + extractMatchResult, cantFailMatchResult, matchCanFail, + mkCoreTupTy, selectSimpleMatchVarL, lookupEvidence, selectMatchVar ) +import DsArrows ( dsProcExpr ) +import DsMonad + +#ifdef GHCI + -- Template Haskell stuff iff bootstrapped +import DsMeta ( dsBracket ) +#endif + +import HsSyn +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, isUnLiftedType, Type, mkAppTy ) +import Type ( funArgTy, splitFunTys, isUnboxedTupleType, mkFunTy ) +import CoreSyn +import CoreUtils ( exprType, mkIfThenElse, bindNonRec ) + +import CostCentre ( mkUserCC ) +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 TyCon ( FieldLabel, tyConDataCons ) +import TysWiredIn ( tupleCon ) +import BasicTypes ( RecFlag(..), Boxity(..), ipNameName ) +import PrelNames ( toPName, + returnMName, bindMName, thenMName, failMName, + mfixName ) +import SrcLoc ( Located(..), unLoc, getLoc, noLoc ) +import Util ( zipEqual, zipWithEqual ) +import Bag ( bagToList ) +import Outputable +import FastString +\end{code} + + +%************************************************************************ +%* * + dsLocalBinds, dsValBinds +%* * +%************************************************************************ + +\begin{code} +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 + 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 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.) + 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) + + 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 + -- Namely, for an AbsBind with no tyvars and no dicts, + -- but which does have dictionary bindings. + -- See notes with TcSimplify.inferLoop [NO TYVARS] + -- It turned out that wrapping a Rec here was the easiest solution + -- + -- 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} + +%************************************************************************ +%* * +\subsection[DsExpr-vars-and-cons]{Variables, constructors, literals} +%* * +%************************************************************************ + +\begin{code} +dsLExpr :: LHsExpr Id -> DsM CoreExpr +dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e + +dsExpr :: HsExpr Id -> DsM CoreExpr + +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 +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) -> + returnDs (mkLams binders matching_code) + +#if defined(GHCI) && defined(BREAKPOINT) +dsExpr (HsApp (L _ (HsApp realFun@(L _ (HsCoerce _ fun)) (L loc arg))) _) + | HsVar funId <- fun + , idName funId == breakpointJumpName + , ids <- filter (not.hasTyVar.idType) (extractIds arg) + = do dsWarn (text "Extracted ids:" <+> ppr ids <+> ppr (map idType ids)) + stablePtr <- ioToIOEnv $ newStablePtr ids + -- Yes, I know... I'm gonna burn in hell. + let Ptr addr# = castStablePtrToPtr stablePtr + funCore <- dsLExpr realFun + argCore <- dsLExpr (L loc (HsLit (HsInt (fromIntegral (I# (addr2Int# addr#)))))) + hvalCore <- dsLExpr (L loc (extractHVals ids)) + return ((funCore `App` argCore) `App` hvalCore) + where extractIds :: HsExpr Id -> [Id] + extractIds (HsApp fn arg) + | HsVar argId <- unLoc arg + = argId:extractIds (unLoc fn) + | TyApp arg' ts <- unLoc arg + , HsVar argId <- unLoc arg' + = error (showSDoc (ppr ts)) -- argId:extractIds (unLoc fn) + extractIds x = [] + extractHVals ids = ExplicitList unitTy (map (L loc . HsVar) ids) + hasTyVar (TyVarTy _) = True + hasTyVar (FunTy a b) = hasTyVar a || hasTyVar b + hasTyVar (NoteTy _ t) = hasTyVar t + hasTyVar (AppTy a b) = hasTyVar a || hasTyVar b + hasTyVar (TyConApp _ ts) = any hasTyVar ts + hasTyVar _ = False +#endif + +dsExpr expr@(HsApp fun arg) + = dsLExpr fun `thenDs` \ core_fun -> + dsLExpr arg `thenDs` \ core_arg -> + returnDs (core_fun `App` core_arg) +\end{code} + +Operator sections. At first it looks as if we can convert +\begin{verbatim} + (expr op) +\end{verbatim} +to +\begin{verbatim} + \x -> op expr x +\end{verbatim} + +But no! expr might be a redex, and we can lose laziness badly this +way. Consider +\begin{verbatim} + map (expr op) xs +\end{verbatim} +for example. So we convert instead to +\begin{verbatim} + let y = expr in \x -> op y x +\end{verbatim} +If \tr{expr} is actually just a variable, say, then the simplifier +will sort it out. + +\begin{code} +dsExpr (OpApp e1 op _ e2) + = dsLExpr op `thenDs` \ core_op -> + -- for the type of y, we need the type of op's 2nd argument + dsLExpr e1 `thenDs` \ x_core -> + dsLExpr e2 `thenDs` \ y_core -> + returnDs (mkApps core_op [x_core, y_core]) + +dsExpr (SectionL expr op) + = dsLExpr op `thenDs` \ core_op -> + -- for the type of y, we need the type of op's 2nd argument + let + (x_ty:y_ty:_, _) = splitFunTys (exprType core_op) + -- Must look through an implicit-parameter type; + -- newtype impossible; hence Type.splitFunTys + in + dsLExpr expr `thenDs` \ x_core -> + newSysLocalDs x_ty `thenDs` \ x_id -> + newSysLocalDs y_ty `thenDs` \ y_id -> + + returnDs (bindNonRec x_id x_core $ + Lam y_id (mkApps core_op [Var x_id, Var y_id])) + +-- dsLExpr (SectionR op expr) -- \ x -> op x expr +dsExpr (SectionR op expr) + = dsLExpr op `thenDs` \ core_op -> + -- for the type of x, we need the type of op's 2nd argument + let + (x_ty:y_ty:_, _) = splitFunTys (exprType core_op) + -- See comment with SectionL + in + dsLExpr expr `thenDs` \ y_core -> + newSysLocalDs x_ty `thenDs` \ x_id -> + newSysLocalDs y_ty `thenDs` \ y_id -> + + returnDs (bindNonRec y_id y_core $ + Lam x_id (mkApps core_op [Var x_id, Var y_id])) + +dsExpr (HsSCC cc expr) + = dsLExpr expr `thenDs` \ core_expr -> + getModuleDs `thenDs` \ mod_name -> + returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr) + + +-- hdaume: core annotation + +dsExpr (HsCoreAnn fs expr) + = dsLExpr expr `thenDs` \ core_expr -> + returnDs (Note (CoreNote $ unpackFS fs) core_expr) + +dsExpr (HsCase discrim matches) + = dsLExpr discrim `thenDs` \ core_discrim -> + matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) -> + returnDs (scrungleMatch discrim_var core_discrim matching_code) + +dsExpr (HsLet binds body) + = dsLExpr body `thenDs` \ 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 body result_ty) + = -- Special case for list comprehensions + dsListComp stmts body elt_ty + where + [elt_ty] = tcTyConAppArgs 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 body result_ty) + = -- Special case for array comprehensions + dsPArrComp (map unLoc stmts) body elt_ty + where + [elt_ty] = tcTyConAppArgs result_ty + +dsExpr (HsIf guard_expr then_expr else_expr) + = dsLExpr guard_expr `thenDs` \ core_guard -> + dsLExpr then_expr `thenDs` \ core_then -> + dsLExpr else_expr `thenDs` \ core_else -> + returnDs (mkIfThenElse core_guard core_then core_else) +\end{code} + + +\noindent +\underline{\bf Type lambda and application} +% ~~~~~~~~~~~~~~~~~~~~~~~~~~~ +\begin{code} +dsExpr (TyLam tyvars expr) + = dsLExpr expr `thenDs` \ core_expr -> + returnDs (mkLams tyvars core_expr) + +dsExpr (TyApp expr tys) + = dsLExpr expr `thenDs` \ core_expr -> + returnDs (mkTyApps core_expr tys) +\end{code} + + +\noindent +\underline{\bf Various data construction things} +% ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +\begin{code} +dsExpr (ExplicitList ty xs) + = go xs + where + go [] = returnDs (mkNilExpr ty) + go (x:xs) = dsLExpr x `thenDs` \ core_x -> + go xs `thenDs` \ core_xs -> + returnDs (mkConsExpr ty core_x core_xs) + +-- 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 +-- 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 +-- that we can exploit the fact that we already know the length of the array +-- here at compile time +-- +dsExpr (ExplicitPArr ty xs) + = dsLookupGlobalId toPName `thenDs` \toP -> + dsExpr (ExplicitList ty xs) `thenDs` \coreList -> + returnDs (mkApps (Var toP) [Type ty, coreList]) + +dsExpr (ExplicitTuple expr_list boxity) + = mappM dsLExpr expr_list `thenDs` \ core_exprs -> + returnDs (mkConApp (tupleCon boxity (length expr_list)) + (map (Type . exprType) core_exprs ++ core_exprs)) + +dsExpr (ArithSeq expr (From from)) + = dsExpr expr `thenDs` \ expr2 -> + dsLExpr from `thenDs` \ from2 -> + returnDs (App expr2 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 (ArithSeq expr (FromThen from thn)) + = dsExpr expr `thenDs` \ expr2 -> + dsLExpr from `thenDs` \ from2 -> + dsLExpr thn `thenDs` \ thn2 -> + returnDs (mkApps expr2 [from2, thn2]) + +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 (PArrSeq expr (FromTo from two)) + = dsExpr expr `thenDs` \ expr2 -> + dsLExpr from `thenDs` \ from2 -> + dsLExpr two `thenDs` \ two2 -> + returnDs (mkApps expr2 [from2, two2]) + +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 (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 +\end{code} + +\noindent +\underline{\bf Record construction and update} +% ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +For record construction we do this (assuming T has three arguments) +\begin{verbatim} + T { op2 = e } +==> + let err = /\a -> recConErr a + T (recConErr t1 "M.lhs/230/op1") + e + (recConErr t1 "M.lhs/230/op3") +\end{verbatim} +@recConErr@ then converts its arugment string into a proper message +before printing it as +\begin{verbatim} + M.lhs, line 230: missing field op1 was evaluated +\end{verbatim} + +We also handle @C{}@ as valid construction syntax for an unlabelled +constructor @C@, setting all of @C@'s fields to bottom. + +\begin{code} +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; + -- hence TcType.tcSplitFunTys + + mk_arg (arg_ty, lbl) -- Selector id has the field label as its name + = case [rhs | (L _ sel_id, rhs) <- rbinds, lbl == idName sel_id] of + (rhs:rhss) -> ASSERT( null rhss ) + dsLExpr rhs + [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl)) + unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty "" + + labels = dataConFieldLabels (idDataCon data_con_id) + -- The data_con_id is guaranteed to be the wrapper id of the constructor + in + + (if null labels + then mappM unlabelled_bottom arg_tys + else mappM mk_arg (zipEqual "dsExpr:RecordCon" arg_tys labels)) + `thenDs` \ con_args -> + + returnDs (mkApps con_expr' con_args) +\end{code} + +Record update is a little harder. Suppose we have the decl: +\begin{verbatim} + data T = T1 {op1, op2, op3 :: Int} + | T2 {op4, op2 :: Int} + | T3 +\end{verbatim} +Then we translate as follows: +\begin{verbatim} + r { op2 = e } +===> + let op2 = e in + case r of + T1 op1 _ op3 -> T1 op1 op2 op3 + T2 op4 _ -> T2 op4 op2 + other -> recUpdError "M.lhs/230" +\end{verbatim} +It's important that we use the constructor Ids for @T1@, @T2@ etc on the +RHSs, and do not generate a Core constructor application directly, because the constructor +might do some argument-evaluation first; and may have to throw away some +dictionaries. + +\begin{code} +dsExpr (RecordUpd record_expr [] record_in_ty record_out_ty) + = dsLExpr record_expr + +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 + -- necessary so that we don't lose sharing + + let + in_inst_tys = tcTyConAppArgs record_in_ty -- Newtype opaque + out_inst_tys = tcTyConAppArgs record_out_ty -- Newtype opaque + in_out_ty = mkFunTy record_in_ty record_out_ty + + mk_val_arg field old_arg_id + = case [rhs | (L _ sel_id, rhs) <- rbinds, field == idName sel_id] of + (rhs:rest) -> ASSERT(null rest) rhs + [] -> nlHsVar old_arg_id + + mk_alt con + = newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys) `thenDs` \ arg_ids -> + -- 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 + (dataConFieldLabels con) arg_ids + rhs = foldl (\a b -> nlHsApp a b) + (noLoc $ TyApp (nlHsVar (dataConWrapId con)) + out_inst_tys) + val_args + in + returnDs (mkSimpleMatch [noLoc $ ConPatOut (noLoc con) [] [] emptyLHsBinds + (PrefixCon (map nlVarPat arg_ids)) record_in_ty] + rhs) + in + -- Record stuff doesn't work for existentials + -- The type checker checks for this, but we need + -- worry only about the constructors that are to be updated + ASSERT2( all isVanillaDataCon cons_to_upd, ppr expr ) + + -- It's important to generate the match with matchWrapper, + -- and the right hand sides with applications of the wrapper Id + -- so that everything works when we are doing fancy unboxing on the + -- constructor aguments. + mappM mk_alt cons_to_upd `thenDs` \ alts -> + matchWrapper RecUpd (MatchGroup alts in_out_ty) `thenDs` \ ([discrim_var], matching_code) -> + + returnDs (bindNonRec discrim_var record_expr' matching_code) + + where + updated_fields :: [FieldLabel] + updated_fields = [ idName sel_id | (L _ sel_id,_) <- rbinds] + + -- Get the type constructor from the record_in_ty + -- so that we are sure it'll have all its DataCons + -- (In GHCI, it's possible that some TyCons may not have all + -- their constructors, in a module-loop situation.) + tycon = tcTyConAppTyCon record_in_ty + data_cons = tyConDataCons tycon + cons_to_upd = filter has_all_fields data_cons + + has_all_fields :: DataCon -> Bool + has_all_fields con_id + = all (`elem` con_fields) updated_fields + where + con_fields = dataConFieldLabels con_id +\end{code} + + +\noindent +\underline{\bf Dictionary lambda and application} +% ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +@DictLam@ and @DictApp@ turn into the regular old things. +(OLD:) @DictFunApp@ also becomes a curried application, albeit slightly more +complicated; reminiscent of fully-applied constructors. +\begin{code} +dsExpr (DictLam dictvars expr) + = dsLExpr expr `thenDs` \ core_expr -> + returnDs (mkLams dictvars core_expr) + +------------------ + +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 + +\begin{code} +-- Template Haskell stuff + +#ifdef GHCI /* Only if bootstrapping */ +dsExpr (HsBracketOut x ps) = dsBracket x ps +dsExpr (HsSpliceE s) = pprPanic "dsExpr:splice" (ppr s) +#endif + +-- Arrow notation extension +dsExpr (HsProc pat cmd) = dsProcExpr pat cmd +\end{code} + + +\begin{code} + +#ifdef DEBUG +-- HsSyn constructs that just shouldn't be here: +dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig" +#endif + +\end{code} + +%-------------------------------------------------------------------- + +Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're +handled in DsListComp). Basically does the translation given in the +Haskell 98 report: + +\begin{code} +dsDo :: [LStmt Id] + -> LHsExpr Id + -> Type -- Type of the whole expression + -> DsM CoreExpr + +dsDo stmts body result_ty + = go (map unLoc stmts) + where + 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: +----------------------------- +We turn (RecStmt [v1,..vn] stmts) into: + + (v1,..,vn) <- mfix (\~(v1,..vn). do stmts + return (v1,..vn)) + +\begin{code} +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 [mfix_pat] body] + (mkFunTy tup_ty body_ty)) + + -- 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 + + 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 + + mk_tup_pat :: [LPat Id] -> LPat Id + mk_tup_pat [p] = p + mk_tup_pat ps = noLoc $ mkVanillaTuplePat ps Boxed + + mk_ret_tup :: [LHsExpr Id] -> LHsExpr Id + mk_ret_tup [r] = r + mk_ret_tup rs = noLoc $ ExplicitTuple rs Boxed +\end{code} |