{-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE TypeFamilies #-} {- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 Pattern-matching bindings (HsBinds and MonoBinds) Handles @HsBinds@; those at the top level require different handling, in that the @Rec@/@NonRec@/etc structure is thrown away (whereas at lower levels it is preserved with @let@/@letrec@s). -} module GHC.HsToCore.Binds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs, dsSpec , dsHsWrapper, dsEvTerm, dsTcEvBinds, dsTcEvBinds_s, dsEvBinds , dsWarnOrphanRule ) where import GHC.Prelude import GHC.Driver.Session import GHC.Driver.Config import qualified GHC.LanguageExtensions as LangExt import GHC.Unit.Module import {-# SOURCE #-} GHC.HsToCore.Expr ( dsLExpr ) import {-# SOURCE #-} GHC.HsToCore.Match ( matchWrapper ) import GHC.HsToCore.Monad import GHC.HsToCore.Errors.Types import GHC.HsToCore.GuardedRHSs import GHC.HsToCore.Utils import GHC.HsToCore.Pmc ( addTyCs, pmcGRHSs ) import GHC.Hs -- lots of things import GHC.Core -- lots of things import GHC.Core.SimpleOpt ( simpleOptExpr ) import GHC.Core.Opt.OccurAnal ( occurAnalyseExpr ) import GHC.Core.Make import GHC.Core.Utils import GHC.Core.Opt.Arity ( etaExpand ) import GHC.Core.Unfold.Make import GHC.Core.FVs import GHC.Core.Predicate import GHC.Core.TyCon import GHC.Core.Type import GHC.Core.Coercion import GHC.Core.Multiplicity import GHC.Core.Rules import GHC.Core.TyCo.Compare( eqType ) import GHC.Builtin.Names import GHC.Builtin.Types ( naturalTy, typeSymbolKind, charTy ) import GHC.Tc.Types.Evidence import GHC.Types.Id import GHC.Types.Name import GHC.Types.Var.Set import GHC.Types.Var.Env import GHC.Types.Var( EvVar ) import GHC.Types.SrcLoc import GHC.Types.Basic import GHC.Types.Unique.Set( nonDetEltsUniqSet ) import GHC.Data.Maybe import GHC.Data.OrdList import GHC.Data.Graph.Directed import GHC.Data.Bag import GHC.Utils.Constants (debugIsOn) import GHC.Utils.Misc import GHC.Utils.Monad import GHC.Utils.Outputable import GHC.Utils.Panic import GHC.Utils.Panic.Plain import Control.Monad {-********************************************************************** * * Desugaring a MonoBinds * * **********************************************************************-} -- | Desugar top level binds, strict binds are treated like normal -- binds since there is no good time to force before first usage. dsTopLHsBinds :: LHsBinds GhcTc -> DsM (OrdList (Id,CoreExpr)) dsTopLHsBinds binds -- see Note [Strict binds checks] | not (isEmptyBag unlifted_binds) || not (isEmptyBag bang_binds) = do { mapBagM_ (top_level_err UnliftedTypeBinds) unlifted_binds ; mapBagM_ (top_level_err StrictBinds) bang_binds ; return nilOL } | otherwise = do { (force_vars, prs) <- dsLHsBinds binds ; when debugIsOn $ do { xstrict <- xoptM LangExt.Strict ; massertPpr (null force_vars || xstrict) (ppr binds $$ ppr force_vars) } -- with -XStrict, even top-level vars are listed as force vars. ; return (toOL prs) } where unlifted_binds = filterBag (isUnliftedHsBind . unLoc) binds bang_binds = filterBag (isBangedHsBind . unLoc) binds top_level_err bindsType (L loc bind) = putSrcSpanDs (locA loc) $ diagnosticDs (DsTopLevelBindsNotAllowed bindsType bind) -- | Desugar all other kind of bindings, Ids of strict binds are returned to -- later be forced in the binding group body, see Note [Desugar Strict binds] dsLHsBinds :: LHsBinds GhcTc -> DsM ([Id], [(Id,CoreExpr)]) dsLHsBinds binds = do { ds_bs <- mapBagM dsLHsBind binds ; return (foldBag (\(a, a') (b, b') -> (a ++ b, a' ++ b')) id ([], []) ds_bs) } ------------------------ dsLHsBind :: LHsBind GhcTc -> DsM ([Id], [(Id,CoreExpr)]) dsLHsBind (L loc bind) = do dflags <- getDynFlags putSrcSpanDs (locA loc) $ dsHsBind dflags bind -- | Desugar a single binding (or group of recursive binds). dsHsBind :: DynFlags -> HsBind GhcTc -> DsM ([Id], [(Id,CoreExpr)]) -- ^ The Ids of strict binds, to be forced in the body of the -- binding group see Note [Desugar Strict binds] and all -- bindings and their desugared right hand sides. dsHsBind dflags (VarBind { var_id = var , var_rhs = expr }) = do { core_expr <- dsLExpr expr -- Dictionary bindings are always VarBinds, -- so we only need do this here ; let core_bind@(id,_) = makeCorePair dflags var False 0 core_expr force_var = if xopt LangExt.Strict dflags then [id] else [] ; return (force_var, [core_bind]) } dsHsBind dflags b@(FunBind { fun_id = L loc fun , fun_matches = matches , fun_ext = (co_fn, tick) }) = do { (args, body) <- addTyCs FromSource (hsWrapDictBinders co_fn) $ -- FromSource might not be accurate (we don't have any -- origin annotations for things in this module), but at -- worst we do superfluous calls to the pattern match -- oracle. -- addTyCs: Add type evidence to the refinement type -- predicate of the coverage checker -- See Note [Long-distance information] in "GHC.HsToCore.Pmc" matchWrapper (mkPrefixFunRhs (L loc (idName fun))) Nothing matches ; core_wrap <- dsHsWrapper co_fn ; let body' = mkOptTickBox tick body rhs = core_wrap (mkLams args body') core_binds@(id,_) = makeCorePair dflags fun False 0 rhs force_var -- Bindings are strict when -XStrict is enabled | xopt LangExt.Strict dflags , matchGroupArity matches == 0 -- no need to force lambdas = [id] | isBangedHsBind b = [id] | otherwise = [] ; --pprTrace "dsHsBind" (vcat [ ppr fun <+> ppr (idInlinePragma fun) -- , ppr (mg_alts matches) -- , ppr args, ppr core_binds, ppr body']) $ return (force_var, [core_binds]) } dsHsBind dflags (PatBind { pat_lhs = pat, pat_rhs = grhss , pat_ext = (ty, (rhs_tick, var_ticks)) }) = do { rhss_nablas <- pmcGRHSs PatBindGuards grhss ; body_expr <- dsGuarded grhss ty rhss_nablas ; let body' = mkOptTickBox rhs_tick body_expr pat' = decideBangHood dflags pat ; (force_var,sel_binds) <- mkSelectorBinds var_ticks pat body' -- We silently ignore inline pragmas; no makeCorePair -- Not so cool, but really doesn't matter ; let force_var' = if isBangedLPat pat' then [force_var] else [] ; return (force_var', sel_binds) } dsHsBind dflags (XHsBindsLR (AbsBinds { abs_tvs = tyvars, abs_ev_vars = dicts , abs_exports = exports , abs_ev_binds = ev_binds , abs_binds = binds, abs_sig = has_sig })) = do { ds_binds <- addTyCs FromSource (listToBag dicts) $ dsLHsBinds binds -- addTyCs: push type constraints deeper -- for inner pattern match check -- See Check, Note [Long-distance information] ; ds_ev_binds <- dsTcEvBinds_s ev_binds -- dsAbsBinds does the hard work ; dsAbsBinds dflags tyvars dicts exports ds_ev_binds ds_binds has_sig } dsHsBind _ (PatSynBind{}) = panic "dsHsBind: PatSynBind" ----------------------- dsAbsBinds :: DynFlags -> [TyVar] -> [EvVar] -> [ABExport] -> [CoreBind] -- Desugared evidence bindings -> ([Id], [(Id,CoreExpr)]) -- Desugared value bindings -> Bool -- Single binding with signature -> DsM ([Id], [(Id,CoreExpr)]) dsAbsBinds dflags tyvars dicts exports ds_ev_binds (force_vars, bind_prs) has_sig -- A very important common case: one exported variable -- Non-recursive bindings come through this way -- So do self-recursive bindings -- gbl_id = wrap (/\tvs \dicts. let ev_binds -- letrec bind_prs -- in lcl_id) | [export] <- exports , ABE { abe_poly = global_id, abe_mono = local_id , abe_wrap = wrap, abe_prags = prags } <- export , Just force_vars' <- case force_vars of [] -> Just [] [v] | v == local_id -> Just [global_id] _ -> Nothing -- If there is a variable to force, it's just the -- single variable we are binding here = do { core_wrap <- dsHsWrapper wrap -- Usually the identity ; let rhs = core_wrap $ mkLams tyvars $ mkLams dicts $ mkCoreLets ds_ev_binds $ body body | has_sig , [(_, lrhs)] <- bind_prs = lrhs | otherwise = mkLetRec bind_prs (Var local_id) ; (spec_binds, rules) <- dsSpecs rhs prags ; let global_id' = addIdSpecialisations global_id rules main_bind = makeCorePair dflags global_id' (isDefaultMethod prags) (dictArity dicts) rhs ; return (force_vars', main_bind : fromOL spec_binds) } -- Another common case: no tyvars, no dicts -- In this case we can have a much simpler desugaring -- lcl_id{inl-prag} = rhs -- Auxiliary binds -- gbl_id = lcl_id |> co -- Main binds | null tyvars, null dicts = do { let mk_main :: ABExport -> DsM (Id, CoreExpr) mk_main (ABE { abe_poly = gbl_id, abe_mono = lcl_id , abe_wrap = wrap }) -- No SpecPrags (no dicts) -- Can't be a default method (default methods are singletons) = do { core_wrap <- dsHsWrapper wrap ; return ( gbl_id `setInlinePragma` defaultInlinePragma , core_wrap (Var lcl_id)) } ; main_prs <- mapM mk_main exports ; return (force_vars, flattenBinds ds_ev_binds ++ mk_aux_binds bind_prs ++ main_prs ) } -- The general case -- See Note [Desugaring AbsBinds] | otherwise = do { let aux_binds = Rec (mk_aux_binds bind_prs) -- Monomorphic recursion possible, hence Rec new_force_vars = get_new_force_vars force_vars locals = map abe_mono exports all_locals = locals ++ new_force_vars tup_expr = mkBigCoreVarTup all_locals tup_ty = exprType tup_expr ; let poly_tup_rhs = mkLams tyvars $ mkLams dicts $ mkCoreLets ds_ev_binds $ mkLet aux_binds $ tup_expr ; poly_tup_id <- newSysLocalDs ManyTy (exprType poly_tup_rhs) -- Find corresponding global or make up a new one: sometimes -- we need to make new export to desugar strict binds, see -- Note [Desugar Strict binds] ; (exported_force_vars, extra_exports) <- get_exports force_vars ; let mk_bind (ABE { abe_wrap = wrap , abe_poly = global , abe_mono = local, abe_prags = spec_prags }) -- See Note [AbsBinds wrappers] in "GHC.Hs.Binds" = do { tup_id <- newSysLocalDs ManyTy tup_ty ; core_wrap <- dsHsWrapper wrap ; let rhs = core_wrap $ mkLams tyvars $ mkLams dicts $ mkBigTupleSelector all_locals local tup_id $ mkVarApps (Var poly_tup_id) (tyvars ++ dicts) rhs_for_spec = Let (NonRec poly_tup_id poly_tup_rhs) rhs ; (spec_binds, rules) <- dsSpecs rhs_for_spec spec_prags ; let global' = (global `setInlinePragma` defaultInlinePragma) `addIdSpecialisations` rules -- Kill the INLINE pragma because it applies to -- the user written (local) function. The global -- Id is just the selector. Hmm. ; return ((global', rhs) : fromOL spec_binds) } ; export_binds_s <- mapM mk_bind (exports ++ extra_exports) ; return ( exported_force_vars , (poly_tup_id, poly_tup_rhs) : concat export_binds_s) } where mk_aux_binds :: [(Id,CoreExpr)] -> [(Id,CoreExpr)] mk_aux_binds bind_prs = [ makeCorePair dflags lcl_w_inline False 0 rhs | (lcl_id, rhs) <- bind_prs , let lcl_w_inline = lookupVarEnv inline_env lcl_id `orElse` lcl_id ] inline_env :: IdEnv Id -- Maps a monomorphic local Id to one with -- the inline pragma from the source -- The type checker put the inline pragma -- on the *global* Id, so we need to transfer it inline_env = mkVarEnv [ (lcl_id, setInlinePragma lcl_id prag) | ABE { abe_mono = lcl_id, abe_poly = gbl_id } <- exports , let prag = idInlinePragma gbl_id ] global_env :: IdEnv Id -- Maps local Id to its global exported Id global_env = mkVarEnv [ (local, global) | ABE { abe_mono = local, abe_poly = global } <- exports ] -- find variables that are not exported get_new_force_vars lcls = foldr (\lcl acc -> case lookupVarEnv global_env lcl of Just _ -> acc Nothing -> lcl:acc) [] lcls -- find exports or make up new exports for force variables get_exports :: [Id] -> DsM ([Id], [ABExport]) get_exports lcls = foldM (\(glbls, exports) lcl -> case lookupVarEnv global_env lcl of Just glbl -> return (glbl:glbls, exports) Nothing -> do export <- mk_export lcl let glbl = abe_poly export return (glbl:glbls, export:exports)) ([],[]) lcls mk_export local = do global <- newSysLocalDs ManyTy (exprType (mkLams tyvars (mkLams dicts (Var local)))) return (ABE { abe_poly = global , abe_mono = local , abe_wrap = WpHole , abe_prags = SpecPrags [] }) -- | This is where we apply INLINE and INLINABLE pragmas. All we need to -- do is to attach the unfolding information to the Id. -- -- Other decisions about whether to inline are made in -- `calcUnfoldingGuidance` but the decision about whether to then expose -- the unfolding in the interface file is made in `GHC.Iface.Tidy.addExternal` -- using this information. ------------------------ makeCorePair :: DynFlags -> Id -> Bool -> Arity -> CoreExpr -> (Id, CoreExpr) makeCorePair dflags gbl_id is_default_method dict_arity rhs | is_default_method -- Default methods are *always* inlined -- See Note [INLINE and default methods] in GHC.Tc.TyCl.Instance = (gbl_id `setIdUnfolding` mkCompulsoryUnfolding' simpl_opts rhs, rhs) | otherwise = case inlinePragmaSpec inline_prag of NoUserInlinePrag -> (gbl_id, rhs) NoInline {} -> (gbl_id, rhs) Opaque {} -> (gbl_id, rhs) Inlinable {} -> (gbl_id `setIdUnfolding` inlinable_unf, rhs) Inline {} -> inline_pair where simpl_opts = initSimpleOpts dflags inline_prag = idInlinePragma gbl_id inlinable_unf = mkInlinableUnfolding simpl_opts StableUserSrc rhs inline_pair | Just arity <- inlinePragmaSat inline_prag -- Add an Unfolding for an INLINE (but not for NOINLINE) -- And eta-expand the RHS; see Note [Eta-expanding INLINE things] , let real_arity = dict_arity + arity -- NB: The arity passed to mkInlineUnfoldingWithArity -- must take account of the dictionaries = ( gbl_id `setIdUnfolding` mkInlineUnfoldingWithArity simpl_opts StableUserSrc real_arity rhs , etaExpand real_arity rhs) | otherwise = pprTrace "makeCorePair: arity missing" (ppr gbl_id) $ (gbl_id `setIdUnfolding` mkInlineUnfoldingNoArity simpl_opts StableUserSrc rhs, rhs) dictArity :: [Var] -> Arity -- Don't count coercion variables in arity dictArity dicts = count isId dicts {- Note [Desugaring AbsBinds] ~~~~~~~~~~~~~~~~~~~~~~~~~~ In the general AbsBinds case we desugar the binding to this: tup a (d:Num a) = let fm = ...gm... gm = ...fm... in (fm,gm) f a d = case tup a d of { (fm,gm) -> fm } g a d = case tup a d of { (fm,gm) -> fm } Note [Rules and inlining] ~~~~~~~~~~~~~~~~~~~~~~~~~ Common special case: no type or dictionary abstraction This is a bit less trivial than you might suppose The naive way would be to desugar to something like f_lcl = ...f_lcl... -- The "binds" from AbsBinds M.f = f_lcl -- Generated from "exports" But we don't want that, because if M.f isn't exported, it'll be inlined unconditionally at every call site (its rhs is trivial). That would be ok unless it has RULES, which would thereby be completely lost. Bad, bad, bad. Instead we want to generate M.f = ...f_lcl... f_lcl = M.f Now all is cool. The RULES are attached to M.f (by SimplCore), and f_lcl is rapidly inlined away. This does not happen in the same way to polymorphic binds, because they desugar to M.f = /\a. let f_lcl = ...f_lcl... in f_lcl Although I'm a bit worried about whether full laziness might float the f_lcl binding out and then inline M.f at its call site Note [Specialising in no-dict case] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Even if there are no tyvars or dicts, we may have specialisation pragmas. Class methods can generate AbsBinds [] [] [( ... spec-prag] { AbsBinds [tvs] [dicts] ...blah } So the overloading is in the nested AbsBinds. A good example is in GHC.Float: class (Real a, Fractional a) => RealFrac a where round :: (Integral b) => a -> b instance RealFrac Float where {-# SPECIALIZE round :: Float -> Int #-} The top-level AbsBinds for $cround has no tyvars or dicts (because the instance does not). But the method is locally overloaded! Note [Abstracting over tyvars only] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When abstracting over type variable only (not dictionaries), we don't really need to built a tuple and select from it, as we do in the general case. Instead we can take AbsBinds [a,b] [ ([a,b], fg, fl, _), ([b], gg, gl, _) ] { fl = e1 gl = e2 h = e3 } and desugar it to fg = /\ab. let B in e1 gg = /\b. let a = () in let B in S(e2) h = /\ab. let B in e3 where B is the *non-recursive* binding fl = fg a b gl = gg b h = h a b -- See (b); note shadowing! Notice (a) g has a different number of type variables to f, so we must use the mkArbitraryType thing to fill in the gaps. We use a type-let to do that. (b) The local variable h isn't in the exports, and rather than clone a fresh copy we simply replace h by (h a b), where the two h's have different types! Shadowing happens here, which looks confusing but works fine. (c) The result is *still* quadratic-sized if there are a lot of small bindings. So if there are more than some small number (10), we filter the binding set B by the free variables of the particular RHS. Tiresome. Why got to this trouble? It's a common case, and it removes the quadratic-sized tuple desugaring. Less clutter, hopefully faster compilation, especially in a case where there are a *lot* of bindings. Note [Eta-expanding INLINE things] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider foo :: Eq a => a -> a {-# INLINE foo #-} foo x = ... If (foo d) ever gets floated out as a common sub-expression (which can happen as a result of method sharing), there's a danger that we never get to do the inlining, which is a Terribly Bad thing given that the user said "inline"! To avoid this we preemptively eta-expand the definition, so that foo has the arity with which it is declared in the source code. In this example it has arity 2 (one for the Eq and one for x). Doing this should mean that (foo d) is a PAP and we don't share it. Note [Nested arities] ~~~~~~~~~~~~~~~~~~~~~ For reasons that are not entirely clear, method bindings come out looking like this: AbsBinds [] [] [$cfromT <= [] fromT] $cfromT [InlPrag=INLINE] :: T Bool -> Bool { AbsBinds [] [] [fromT <= [] fromT_1] fromT :: T Bool -> Bool { fromT_1 ((TBool b)) = not b } } } Note the nested AbsBind. The arity for the unfolding on $cfromT should be gotten from the binding for fromT_1. It might be better to have just one level of AbsBinds, but that requires more thought! Note [Desugar Strict binds] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ See https://gitlab.haskell.org/ghc/ghc/wikis/strict-pragma Desugaring strict variable bindings looks as follows (core below ==>) let !x = rhs in body ==> let x = rhs in x `seq` body -- seq the variable and if it is a pattern binding the desugaring looks like let !pat = rhs in body ==> let x = rhs -- bind the rhs to a new variable pat = x in x `seq` body -- seq the new variable if there is no variable in the pattern desugaring looks like let False = rhs in body ==> let x = case rhs of {False -> (); _ -> error "Match failed"} in x `seq` body In order to force the Ids in the binding group they are passed around in the dsHsBind family of functions, and later seq'ed in GHC.HsToCore.Expr.ds_val_bind. Consider a recursive group like this letrec f : g = rhs[f,g] in Without `Strict`, we get a translation like this: let t = /\a. letrec tm = rhs[fm,gm] fm = case t of fm:_ -> fm gm = case t of _:gm -> gm in (fm,gm) in let f = /\a. case t a of (fm,_) -> fm in let g = /\a. case t a of (_,gm) -> gm in Here `tm` is the monomorphic binding for `rhs`. With `Strict`, we want to force `tm`, but NOT `fm` or `gm`. Alas, `tm` isn't in scope in the `in ` part. The simplest thing is to return it in the polymorphic tuple `t`, thus: let t = /\a. letrec tm = rhs[fm,gm] fm = case t of fm:_ -> fm gm = case t of _:gm -> gm in (tm, fm, gm) in let f = /\a. case t a of (_,fm,_) -> fm in let g = /\a. case t a of (_,_,gm) -> gm in let tm = /\a. case t a of (tm,_,_) -> tm in tm `seq` See https://gitlab.haskell.org/ghc/ghc/wikis/strict-pragma for a more detailed explanation of the desugaring of strict bindings. Note [Strict binds checks] ~~~~~~~~~~~~~~~~~~~~~~~~~~ There are several checks around properly formed strict bindings. They all link to this Note. These checks must be here in the desugarer because we cannot know whether or not a type is unlifted until after zonking, due to representation polymorphism. These checks all used to be handled in the typechecker in checkStrictBinds (before Jan '17). We define an "unlifted bind" to be any bind that binds an unlifted id. Note that x :: Char (# True, x #) = blah is *not* an unlifted bind. Unlifted binds are detected by GHC.Hs.Utils.isUnliftedHsBind. Define a "banged bind" to have a top-level bang. Detected by GHC.Hs.Pat.isBangedHsBind. Define a "strict bind" to be either an unlifted bind or a banged bind. The restrictions are: 1. Strict binds may not be top-level. Checked in dsTopLHsBinds. 2. Unlifted binds must also be banged. (There is no trouble to compile an unbanged unlifted bind, but an unbanged bind looks lazy, and we don't want users to be surprised by the strictness of an unlifted bind.) Checked in first clause of GHC.HsToCore.Expr.ds_val_bind. 3. Unlifted binds may not have polymorphism (#6078). (That is, no quantified type variables or constraints.) Checked in first clause of GHC.HsToCore.Expr.ds_val_bind. 4. Unlifted binds may not be recursive. Checked in second clause of ds_val_bind. -} ------------------------ dsSpecs :: CoreExpr -- Its rhs -> TcSpecPrags -> DsM ( OrdList (Id,CoreExpr) -- Binding for specialised Ids , [CoreRule] ) -- Rules for the Global Ids -- See Note [Handling SPECIALISE pragmas] in GHC.Tc.Gen.Bind dsSpecs _ IsDefaultMethod = return (nilOL, []) dsSpecs poly_rhs (SpecPrags sps) = do { pairs <- mapMaybeM (dsSpec (Just poly_rhs)) sps ; let (spec_binds_s, rules) = unzip pairs ; return (concatOL spec_binds_s, rules) } dsSpec :: Maybe CoreExpr -- Just rhs => RULE is for a local binding -- Nothing => RULE is for an imported Id -- rhs is in the Id's unfolding -> Located TcSpecPrag -> DsM (Maybe (OrdList (Id,CoreExpr), CoreRule)) dsSpec mb_poly_rhs (L loc (SpecPrag poly_id spec_co spec_inl)) | isJust (isClassOpId_maybe poly_id) = putSrcSpanDs loc $ do { diagnosticDs (DsUselessSpecialiseForClassMethodSelector poly_id) ; return Nothing } -- There is no point in trying to specialise a class op -- Moreover, classops don't (currently) have an inl_sat arity set -- (it would be Just 0) and that in turn makes makeCorePair bleat | no_act_spec && isNeverActive rule_act = putSrcSpanDs loc $ do { diagnosticDs (DsUselessSpecialiseForNoInlineFunction poly_id) ; return Nothing } -- Function is NOINLINE, and the specialisation inherits that -- See Note [Activation pragmas for SPECIALISE] | otherwise = putSrcSpanDs loc $ do { uniq <- newUnique ; let poly_name = idName poly_id spec_occ = mkSpecOcc (getOccName poly_name) spec_name = mkInternalName uniq spec_occ (getSrcSpan poly_name) (spec_bndrs, spec_app) = collectHsWrapBinders spec_co -- spec_co looks like -- \spec_bndrs. [] spec_args -- perhaps with the body of the lambda wrapped in some WpLets -- E.g. /\a \(d:Eq a). let d2 = $df d in [] (Maybe a) d2 ; core_app <- dsHsWrapper spec_app ; let ds_lhs = core_app (Var poly_id) spec_ty = mkLamTypes spec_bndrs (exprType ds_lhs) ; -- pprTrace "dsRule" (vcat [ text "Id:" <+> ppr poly_id -- , text "spec_co:" <+> ppr spec_co -- , text "ds_rhs:" <+> ppr ds_lhs ]) $ dflags <- getDynFlags ; case decomposeRuleLhs dflags spec_bndrs ds_lhs (mkVarSet spec_bndrs) of { Left msg -> do { diagnosticDs msg; return Nothing } ; Right (rule_bndrs, _fn, rule_lhs_args) -> do { this_mod <- getModule ; let fn_unf = realIdUnfolding poly_id simpl_opts = initSimpleOpts dflags spec_unf = specUnfolding simpl_opts spec_bndrs core_app rule_lhs_args fn_unf spec_id = mkLocalId spec_name ManyTy spec_ty -- Specialised binding is toplevel, hence Many. `setInlinePragma` inl_prag `setIdUnfolding` spec_unf rule = mkSpecRule dflags this_mod False rule_act (text "USPEC") poly_id rule_bndrs rule_lhs_args (mkVarApps (Var spec_id) spec_bndrs) spec_rhs = mkLams spec_bndrs (core_app poly_rhs) ; dsWarnOrphanRule rule ; return (Just (unitOL (spec_id, spec_rhs), rule)) -- NB: do *not* use makeCorePair on (spec_id,spec_rhs), because -- makeCorePair overwrites the unfolding, which we have -- just created using specUnfolding } } } where is_local_id = isJust mb_poly_rhs poly_rhs | Just rhs <- mb_poly_rhs = rhs -- Local Id; this is its rhs | Just unfolding <- maybeUnfoldingTemplate (realIdUnfolding poly_id) = unfolding -- Imported Id; this is its unfolding -- Use realIdUnfolding so we get the unfolding -- even when it is a loop breaker. -- We want to specialise recursive functions! | otherwise = pprPanic "dsImpSpecs" (ppr poly_id) -- The type checker has checked that it *has* an unfolding id_inl = idInlinePragma poly_id -- See Note [Activation pragmas for SPECIALISE] inl_prag | not (isDefaultInlinePragma spec_inl) = spec_inl | not is_local_id -- See Note [Specialising imported functions] -- in OccurAnal , isStrongLoopBreaker (idOccInfo poly_id) = neverInlinePragma | otherwise = id_inl -- Get the INLINE pragma from SPECIALISE declaration, or, -- failing that, from the original Id spec_prag_act = inlinePragmaActivation spec_inl -- See Note [Activation pragmas for SPECIALISE] -- no_act_spec is True if the user didn't write an explicit -- phase specification in the SPECIALISE pragma no_act_spec = case inlinePragmaSpec spec_inl of NoInline _ -> isNeverActive spec_prag_act Opaque _ -> isNeverActive spec_prag_act _ -> isAlwaysActive spec_prag_act rule_act | no_act_spec = inlinePragmaActivation id_inl -- Inherit | otherwise = spec_prag_act -- Specified by user dsWarnOrphanRule :: CoreRule -> DsM () dsWarnOrphanRule rule = when (isOrphan (ru_orphan rule)) $ diagnosticDs (DsOrphanRule rule) {- Note [SPECIALISE on INLINE functions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We used to warn that using SPECIALISE for a function marked INLINE would be a no-op; but it isn't! Especially with worker/wrapper split we might have {-# INLINE f #-} f :: Ord a => Int -> a -> ... f d x y = case x of I# x' -> $wf d x' y We might want to specialise 'f' so that we in turn specialise '$wf'. We can't even /name/ '$wf' in the source code, so we can't specialise it even if we wanted to. #10721 is a case in point. Note [Activation pragmas for SPECIALISE] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ From a user SPECIALISE pragma for f, we generate a) A top-level binding spec_fn = rhs b) A RULE f dOrd = spec_fn We need two pragma-like things: * spec_fn's inline pragma: inherited from f's inline pragma (ignoring activation on SPEC), unless overridden by SPEC INLINE * Activation of RULE: from SPECIALISE pragma (if activation given) otherwise from f's inline pragma This is not obvious (see #5237)! Examples Rule activation Inline prag on spec'd fn --------------------------------------------------------------------- SPEC [n] f :: ty [n] Always, or NOINLINE [n] copy f's prag NOINLINE f SPEC [n] f :: ty [n] NOINLINE copy f's prag NOINLINE [k] f SPEC [n] f :: ty [n] NOINLINE [k] copy f's prag INLINE [k] f SPEC [n] f :: ty [n] INLINE [k] copy f's prag SPEC INLINE [n] f :: ty [n] INLINE [n] (ignore INLINE prag on f, same activation for rule and spec'd fn) NOINLINE [k] f SPEC f :: ty [n] INLINE [k] ************************************************************************ * * \subsection{Adding inline pragmas} * * ************************************************************************ -} decomposeRuleLhs :: DynFlags -> [Var] -> CoreExpr -> VarSet -- Free vars of the RHS -> Either DsMessage ([Var], Id, [CoreExpr]) -- (decomposeRuleLhs bndrs lhs) takes apart the LHS of a RULE, -- The 'bndrs' are the quantified binders of the rules, but decomposeRuleLhs -- may add some extra dictionary binders (see Note [Free dictionaries on rule LHS]) -- -- Returns an error message if the LHS isn't of the expected shape -- Note [Decomposing the left-hand side of a RULE] decomposeRuleLhs dflags orig_bndrs orig_lhs rhs_fvs | Var funId <- fun2 , Just con <- isDataConId_maybe funId = Left (DsRuleIgnoredDueToConstructor con) -- See Note [No RULES on datacons] | otherwise = case decompose fun2 args2 of Nothing -> Left (DsRuleLhsTooComplicated orig_lhs lhs2) Just (fn_id, args) | not (null unbound) -> -- Check for things unbound on LHS -- See Note [Unused spec binders] -- pprTrace "decomposeRuleLhs 1" (vcat [ text "orig_bndrs:" <+> ppr orig_bndrs -- , text "orig_lhs:" <+> ppr orig_lhs -- , text "lhs_fvs:" <+> ppr lhs_fvs -- , text "rhs_fvs:" <+> ppr rhs_fvs -- , text "unbound:" <+> ppr unbound -- ]) $ Left (DsRuleBindersNotBound unbound orig_bndrs orig_lhs lhs2) | otherwise -> -- pprTrace "decomposeRuleLhs 2" (vcat [ text "orig_bndrs:" <+> ppr orig_bndrs -- , text "orig_lhs:" <+> ppr orig_lhs -- , text "lhs1:" <+> ppr lhs1 -- , text "extra_bndrs:" <+> ppr extra_bndrs -- , text "fn_id:" <+> ppr fn_id -- , text "args:" <+> ppr args -- , text "args fvs:" <+> ppr (exprsFreeVarsList args) -- ]) $ Right (trimmed_bndrs ++ extra_bndrs, fn_id, args) where -- See Note [Variables unbound on the LHS] lhs_fvs = exprsFreeVars args all_fvs = lhs_fvs `unionVarSet` rhs_fvs trimmed_bndrs = filter (`elemVarSet` all_fvs) orig_bndrs unbound = filterOut (`elemVarSet` lhs_fvs) trimmed_bndrs -- Needed on RHS but not bound on LHS -- Add extra tyvar binders: Note [Free tyvars on rule LHS] -- and extra dict binders: Note [Free dictionaries on rule LHS] extra_bndrs = scopedSort extra_tvs ++ extra_dicts where extra_tvs = [ v | v <- extra_vars, isTyVar v ] extra_dicts = [ mkLocalId (localiseName (idName d)) ManyTy (idType d) | d <- extra_vars, isDictId d ] extra_vars = [ v | v <- exprsFreeVarsList args , not (v `elemVarSet` orig_bndr_set) , not (v == fn_id) ] -- fn_id: do not quantify over the function itself, which may -- itself be a dictionary (in pathological cases, #10251) where simpl_opts = initSimpleOpts dflags orig_bndr_set = mkVarSet orig_bndrs lhs1 = drop_dicts orig_lhs lhs2 = simpleOptExpr simpl_opts lhs1 -- See Note [Simplify rule LHS] (fun2,args2) = collectArgs lhs2 decompose (Var fn_id) args | not (fn_id `elemVarSet` orig_bndr_set) = Just (fn_id, args) decompose _ _ = Nothing drop_dicts :: CoreExpr -> CoreExpr drop_dicts e = wrap_lets needed bnds body where needed = orig_bndr_set `minusVarSet` exprFreeVars body (bnds, body) = split_lets (occurAnalyseExpr e) -- The occurAnalyseExpr drops dead bindings which is -- crucial to ensure that every binding is used later; -- which in turn makes wrap_lets work right split_lets :: CoreExpr -> ([(DictId,CoreExpr)], CoreExpr) split_lets (Let (NonRec d r) body) | isDictId d = ((d,r):bs, body') where (bs, body') = split_lets body -- handle "unlifted lets" too, needed for "map/coerce" split_lets (Case r d _ [Alt DEFAULT _ body]) | isCoVar d = ((d,r):bs, body') where (bs, body') = split_lets body split_lets e = ([], e) wrap_lets :: VarSet -> [(DictId,CoreExpr)] -> CoreExpr -> CoreExpr wrap_lets _ [] body = body wrap_lets needed ((d, r) : bs) body | rhs_fvs `intersectsVarSet` needed = mkCoreLet (NonRec d r) (wrap_lets needed' bs body) | otherwise = wrap_lets needed bs body where rhs_fvs = exprFreeVars r needed' = (needed `minusVarSet` rhs_fvs) `extendVarSet` d {- Note [Variables unbound on the LHS] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We obviously want to complain about RULE forall x. f True = not x because the forall'd variable `x` is not bound on the LHS. It can be a bit delicate when dictionaries are involved. Consider #22471 {-# RULES "foo" forall (f :: forall a. [a] -> Int). foo (\xs. 1 + f xs) = 2 + foo f #-} We get two dicts on the LHS, one from `1` and one from `+`. For reasons described in Note [The SimplifyRule Plan] in GHC.Tc.Gen.Rule, we quantify separately over those dictionaries: forall f (d1::Num Int) (d2 :: Num Int). foo (\xs. (+) d1 (fromInteger d2 1) xs) = ... Now the desugarer shortcircuits (fromInteger d2 1) to (I# 1); so d2 is not mentioned at all (on LHS or RHS)! We don't want to complain about and unbound d2. Hence the trimmed_bndrs. Note [Decomposing the left-hand side of a RULE] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There are several things going on here. * drop_dicts: see Note [Drop dictionary bindings on rule LHS] * simpleOptExpr: see Note [Simplify rule LHS] * extra_dict_bndrs: see Note [Free dictionaries on rule LHS] Note [Free tyvars on rule LHS] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data T a = C foo :: T a -> Int foo C = 1 {-# RULES "myrule" foo C = 1 #-} After type checking the LHS becomes (foo alpha (C alpha)), where alpha is an unbound meta-tyvar. The zonker in GHC.Tc.Utils.Zonk is careful not to turn the free alpha into Any (as it usually does). Instead it turns it into a TyVar 'a'. See Note [Zonking the LHS of a RULE] in "GHC.Tc.Utils.Zonk". Now we must quantify over that 'a'. It's /really/ inconvenient to do that in the zonker, because the HsExpr data type is very large. But it's /easy/ to do it here in the desugarer. Moreover, we have to do something rather similar for dictionaries; see Note [Free dictionaries on rule LHS]. So that's why we look for type variables free on the LHS, and quantify over them. This relies on there not being any in-scope tyvars, which is true for user-defined RULEs, which are always top-level. Note [Free dictionaries on rule LHS] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When the LHS of a specialisation rule, (/\as\ds. f es) has a free dict, which is presumably in scope at the function definition site, we can quantify over it too. *Any* dict with that type will do. So for example when you have f :: Eq a => a -> a f = ... SPECIALISE f :: Int -> Int ... Then we get the SpecPrag SpecPrag (f Int dInt) And from that we want the rule RULE forall dInt. f Int dInt = f_spec f_spec = let f = in f Int dInt But be careful! That dInt might be GHC.Base.$fOrdInt, which is an External Name, and you can't bind them in a lambda or forall without getting things confused. Likewise it might have a stable unfolding or something, which would be utterly bogus. So we really make a fresh Id, with the same unique and type as the old one, but with an Internal name and no IdInfo. Note [Drop dictionary bindings on rule LHS] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ drop_dicts drops dictionary bindings on the LHS where possible. E.g. let d:Eq [Int] = $fEqList $fEqInt in f d --> f d Reasoning here is that there is only one d:Eq [Int], and so we can quantify over it. That makes 'd' free in the LHS, but that is later picked up by extra_dict_bndrs (see Note [Unused spec binders]). NB 1: We can only drop the binding if the RHS doesn't bind one of the orig_bndrs, which we assume occur on RHS. Example f :: (Eq a) => b -> a -> a {-# SPECIALISE f :: Eq a => b -> [a] -> [a] #-} Here we want to end up with RULE forall d:Eq a. f ($dfEqList d) = f_spec d Of course, the ($dfEqlist d) in the pattern makes it less likely to match, but there is no other way to get d:Eq a NB 2: We do drop_dicts *before* simplOptEpxr, so that we expect all the evidence bindings to be wrapped around the outside of the LHS. (After simplOptExpr they'll usually have been inlined.) dsHsWrapper does dependency analysis, so that civilised ones will be simple NonRec bindings. We don't handle recursive dictionaries! NB3: In the common case of a non-overloaded, but perhaps-polymorphic specialisation, we don't need to bind *any* dictionaries for use in the RHS. For example (#8331) {-# SPECIALIZE INLINE useAbstractMonad :: ReaderST s Int #-} useAbstractMonad :: MonadAbstractIOST m => m Int Here, deriving (MonadAbstractIOST (ReaderST s)) is a lot of code but the RHS uses no dictionaries, so we want to end up with RULE forall s (d :: MonadAbstractIOST (ReaderT s)). useAbstractMonad (ReaderT s) d = $suseAbstractMonad s #8848 is a good example of where there are some interesting dictionary bindings to discard. The drop_dicts algorithm is based on these observations: * Given (let d = rhs in e) where d is a DictId, matching 'e' will bind e's free variables. * So we want to keep the binding if one of the needed variables (for which we need a binding) is in fv(rhs) but not already in fv(e). * The "needed variables" are simply the orig_bndrs. Consider f :: (Eq a, Show b) => a -> b -> String ... SPECIALISE f :: (Show b) => Int -> b -> String ... Then orig_bndrs includes the *quantified* dictionaries of the type namely (dsb::Show b), but not the one for Eq Int So we work inside out, applying the above criterion at each step. Note [Simplify rule LHS] ~~~~~~~~~~~~~~~~~~~~~~~~ simplOptExpr occurrence-analyses and simplifies the LHS: (a) Inline any remaining dictionary bindings (which hopefully occur just once) (b) Substitute trivial lets, so that they don't get in the way. Note that we substitute the function too; we might have this as a LHS: let f71 = M.f Int in f71 (c) Do eta reduction. To see why, consider the fold/build rule, which without simplification looked like: fold k z (build (/\a. g a)) ==> ... This doesn't match unless you do eta reduction on the build argument. Similarly for a LHS like augment g (build h) we do not want to get augment (\a. g a) (build h) otherwise we don't match when given an argument like augment (\a. h a a) (build h) Note [Unused spec binders] ~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider f :: a -> a ... SPECIALISE f :: Eq a => a -> a ... It's true that this *is* a more specialised type, but the rule we get is something like this: f_spec d = f RULE: f = f_spec d Note that the rule is bogus, because it mentions a 'd' that is not bound on the LHS! But it's a silly specialisation anyway, because the constraint is unused. We could bind 'd' to (error "unused") but it seems better to reject the program because it's almost certainly a mistake. That's what the isDeadBinder call detects. Note [No RULES on datacons] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Previously, `RULES` like "JustNothing" forall x . Just x = Nothing were allowed. Simon Peyton Jones says this seems to have been a mistake, that such rules have never been supported intentionally, and that he doesn't know if they can break in horrible ways. Furthermore, Ben Gamari and Reid Barton are considering trying to detect the presence of "static data" that the simplifier doesn't need to traverse at all. Such rules do not play well with that. So for now, we ban them altogether as requested by #13290. See also #7398. ************************************************************************ * * Desugaring evidence * * ************************************************************************ Note [Desugaring WpFun] ~~~~~~~~~~~~~~~~~~~~~~~ See comments on WpFun in GHC.Tc.Types.Evidence for what WpFun means. Roughly: (WpFun w_arg w_res)[ e ] = \x. w_res[ e w_arg[x] ] This eta-expansion risk duplicating work, if `e` is not in HNF. At one stage I thought we could avoid that by desugaring to let f = e in \x. w_res[ f w_arg[x] ] But that /fundamentally/ doesn't work, because `w_res` may bind evidence that is used in `e`. This question arose when thinking about deep subsumption; see https://github.com/ghc-proposals/ghc-proposals/pull/287#issuecomment-1125419649). -} dsHsWrapper :: HsWrapper -> DsM (CoreExpr -> CoreExpr) dsHsWrapper WpHole = return $ \e -> e dsHsWrapper (WpTyApp ty) = return $ \e -> App e (Type ty) dsHsWrapper (WpEvLam ev) = return $ Lam ev dsHsWrapper (WpTyLam tv) = return $ Lam tv dsHsWrapper (WpLet ev_binds) = do { bs <- dsTcEvBinds ev_binds ; return (mkCoreLets bs) } dsHsWrapper (WpCompose c1 c2) = do { w1 <- dsHsWrapper c1 ; w2 <- dsHsWrapper c2 ; return (w1 . w2) } dsHsWrapper (WpFun c1 c2 (Scaled w t1)) -- See Note [Desugaring WpFun] = do { x <- newSysLocalDs w t1 ; w1 <- dsHsWrapper c1 ; w2 <- dsHsWrapper c2 ; let app f a = mkCoreAppDs (text "dsHsWrapper") f a arg = w1 (Var x) ; return (\e -> (Lam x (w2 (app e arg)))) } dsHsWrapper (WpCast co) = assert (coercionRole co == Representational) $ return $ \e -> mkCastDs e co dsHsWrapper (WpEvApp tm) = do { core_tm <- dsEvTerm tm ; return (\e -> App e core_tm) } -- See Note [Wrapper returned from tcSubMult] in GHC.Tc.Utils.Unify. dsHsWrapper (WpMultCoercion co) = do { when (not (isReflexiveCo co)) $ diagnosticDs DsMultiplicityCoercionsNotSupported ; return $ \e -> e } -------------------------------------- dsTcEvBinds_s :: [TcEvBinds] -> DsM [CoreBind] dsTcEvBinds_s [] = return [] dsTcEvBinds_s (b:rest) = assert (null rest) $ -- Zonker ensures null dsTcEvBinds b dsTcEvBinds :: TcEvBinds -> DsM [CoreBind] dsTcEvBinds (TcEvBinds {}) = panic "dsEvBinds" -- Zonker has got rid of this dsTcEvBinds (EvBinds bs) = dsEvBinds bs dsEvBinds :: Bag EvBind -> DsM [CoreBind] dsEvBinds bs = do { ds_bs <- mapBagM dsEvBind bs ; return (mk_ev_binds ds_bs) } mk_ev_binds :: Bag (Id,CoreExpr) -> [CoreBind] -- We do SCC analysis of the evidence bindings, /after/ desugaring -- them. This is convenient: it means we can use the GHC.Core -- free-variable functions rather than having to do accurate free vars -- for EvTerm. mk_ev_binds ds_binds = map ds_scc (stronglyConnCompFromEdgedVerticesUniq edges) where edges :: [ Node EvVar (EvVar,CoreExpr) ] edges = foldr ((:) . mk_node) [] ds_binds mk_node :: (Id, CoreExpr) -> Node EvVar (EvVar,CoreExpr) mk_node b@(var, rhs) = DigraphNode { node_payload = b , node_key = var , node_dependencies = nonDetEltsUniqSet $ exprFreeVars rhs `unionVarSet` coVarsOfType (varType var) } -- It's OK to use nonDetEltsUniqSet here as stronglyConnCompFromEdgedVertices -- is still deterministic even if the edges are in nondeterministic order -- as explained in Note [Deterministic SCC] in GHC.Data.Graph.Directed. ds_scc (AcyclicSCC (v,r)) = NonRec v r ds_scc (CyclicSCC prs) = Rec prs dsEvBind :: EvBind -> DsM (Id, CoreExpr) dsEvBind (EvBind { eb_lhs = v, eb_rhs = r}) = liftM ((,) v) (dsEvTerm r) {-********************************************************************** * * Desugaring EvTerms * * **********************************************************************-} dsEvTerm :: EvTerm -> DsM CoreExpr dsEvTerm (EvExpr e) = return e dsEvTerm (EvTypeable ty ev) = dsEvTypeable ty ev dsEvTerm (EvFun { et_tvs = tvs, et_given = given , et_binds = ev_binds, et_body = wanted_id }) = do { ds_ev_binds <- dsTcEvBinds ev_binds ; return $ (mkLams (tvs ++ given) $ mkCoreLets ds_ev_binds $ Var wanted_id) } {-********************************************************************** * * Desugaring Typeable dictionaries * * **********************************************************************-} dsEvTypeable :: Type -> EvTypeable -> DsM CoreExpr -- Return a CoreExpr :: Typeable ty -- This code is tightly coupled to the representation -- of TypeRep, in base library Data.Typeable.Internal dsEvTypeable ty ev = do { tyCl <- dsLookupTyCon typeableClassName -- Typeable ; let kind = typeKind ty typeable_data_con = tyConSingleDataCon tyCl -- "Data constructor" -- for Typeable ; rep_expr <- ds_ev_typeable ty ev -- :: TypeRep a -- Package up the method as `Typeable` dictionary ; return $ mkConApp typeable_data_con [Type kind, Type ty, rep_expr] } type TypeRepExpr = CoreExpr -- | Returns a @CoreExpr :: TypeRep ty@ ds_ev_typeable :: Type -> EvTypeable -> DsM CoreExpr ds_ev_typeable ty (EvTypeableTyCon tc kind_ev) = do { mkTrCon <- dsLookupGlobalId mkTrConName -- mkTrCon :: forall k (a :: k). TyCon -> TypeRep k -> TypeRep a ; someTypeRepTyCon <- dsLookupTyCon someTypeRepTyConName ; someTypeRepDataCon <- dsLookupDataCon someTypeRepDataConName -- SomeTypeRep :: forall k (a :: k). TypeRep a -> SomeTypeRep ; tc_rep <- tyConRep tc -- :: TyCon ; let ks = tyConAppArgs ty -- Construct a SomeTypeRep toSomeTypeRep :: Type -> EvTerm -> DsM CoreExpr toSomeTypeRep t ev = do rep <- getRep ev t return $ mkCoreConApps someTypeRepDataCon [Type (typeKind t), Type t, rep] ; kind_arg_reps <- sequence $ zipWith toSomeTypeRep ks kind_ev -- :: TypeRep t ; let -- :: [SomeTypeRep] kind_args = mkListExpr (mkTyConTy someTypeRepTyCon) kind_arg_reps -- Note that we use the kind of the type, not the TyCon from which it -- is constructed since the latter may be kind polymorphic whereas the -- former we know is not (we checked in the solver). ; let expr = mkApps (Var mkTrCon) [ Type (typeKind ty) , Type ty , tc_rep , kind_args ] -- ; pprRuntimeTrace "Trace mkTrTyCon" (ppr expr) expr ; return expr } ds_ev_typeable ty (EvTypeableTyApp ev1 ev2) | Just (t1,t2) <- splitAppTy_maybe ty = do { e1 <- getRep ev1 t1 ; e2 <- getRep ev2 t2 ; mkTrApp <- dsLookupGlobalId mkTrAppName -- mkTrApp :: forall k1 k2 (a :: k1 -> k2) (b :: k1). -- TypeRep a -> TypeRep b -> TypeRep (a b) ; let (_, k1, k2) = splitFunTy (typeKind t1) -- drop the multiplicity, -- since it's a kind ; let expr = mkApps (mkTyApps (Var mkTrApp) [ k1, k2, t1, t2 ]) [ e1, e2 ] -- ; pprRuntimeTrace "Trace mkTrApp" (ppr expr) expr ; return expr } ds_ev_typeable ty (EvTypeableTrFun evm ev1 ev2) | Just (_af,m,t1,t2) <- splitFunTy_maybe ty = do { e1 <- getRep ev1 t1 ; e2 <- getRep ev2 t2 ; em <- getRep evm m ; mkTrFun <- dsLookupGlobalId mkTrFunName -- mkTrFun :: forall (m :: Multiplicity) r1 r2 (a :: TYPE r1) (b :: TYPE r2). -- TypeRep m -> TypeRep a -> TypeRep b -> TypeRep (a % m -> b) ; let r1 = getRuntimeRep t1 r2 = getRuntimeRep t2 ; return $ mkApps (mkTyApps (Var mkTrFun) [m, r1, r2, t1, t2]) [ em, e1, e2 ] } ds_ev_typeable ty (EvTypeableTyLit ev) = -- See Note [Typeable for Nat and Symbol] in GHC.Tc.Solver.Interact do { fun <- dsLookupGlobalId tr_fun ; dict <- dsEvTerm ev -- Of type KnownNat/KnownSymbol ; return (mkApps (mkTyApps (Var fun) [ty]) [ dict ]) } where ty_kind = typeKind ty -- tr_fun is the Name of -- typeNatTypeRep :: KnownNat a => TypeRep a -- of typeSymbolTypeRep :: KnownSymbol a => TypeRep a tr_fun | ty_kind `eqType` naturalTy = typeNatTypeRepName | ty_kind `eqType` typeSymbolKind = typeSymbolTypeRepName | ty_kind `eqType` charTy = typeCharTypeRepName | otherwise = panic "dsEvTypeable: unknown type lit kind" ds_ev_typeable ty ev = pprPanic "dsEvTypeable" (ppr ty $$ ppr ev) getRep :: EvTerm -- ^ EvTerm for @Typeable ty@ -> Type -- ^ The type @ty@ -> DsM TypeRepExpr -- ^ Return @CoreExpr :: TypeRep ty@ -- namely @typeRep# dict@ -- Remember that -- typeRep# :: forall k (a::k). Typeable k a -> TypeRep a getRep ev ty = do { typeable_expr <- dsEvTerm ev ; typeRepId <- dsLookupGlobalId typeRepIdName ; let ty_args = [typeKind ty, ty] ; return (mkApps (mkTyApps (Var typeRepId) ty_args) [ typeable_expr ]) } tyConRep :: TyCon -> DsM CoreExpr -- Returns CoreExpr :: TyCon tyConRep tc | Just tc_rep_nm <- tyConRepName_maybe tc = do { tc_rep_id <- dsLookupGlobalId tc_rep_nm ; return (Var tc_rep_id) } | otherwise = pprPanic "tyConRep" (ppr tc)