2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Pattern-matching bindings (HsBinds and MonoBinds)
8 Handles @HsBinds@; those at the top level require different handling,
9 in that the @Rec@/@NonRec@/etc structure is thrown away (whereas at
10 lower levels it is preserved with @let@/@letrec@s).
13 module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs,
18 #include "HsVersions.h"
20 import {-# SOURCE #-} DsExpr( dsLExpr, dsExpr )
21 import {-# SOURCE #-} Match( matchWrapper )
28 import HsSyn -- lots of things
29 import CoreSyn -- lots of things
35 import TcHsSyn ( mkArbitraryType ) -- Mis-placed?
40 import Var ( Var, TyVar )
49 import BasicTypes hiding ( TopLevel )
51 import StaticFlags ( opt_DsMultiTyVar )
52 import Util ( mapSnd, count, mapAndUnzip, lengthExceeds )
58 %************************************************************************
60 \subsection[dsMonoBinds]{Desugaring a @MonoBinds@}
62 %************************************************************************
65 dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
66 dsTopLHsBinds auto_scc binds = ds_lhs_binds auto_scc binds
68 dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)]
69 dsLHsBinds binds = ds_lhs_binds NoSccs binds
72 ------------------------
73 ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)]
75 -- scc annotation policy (see below)
76 ds_lhs_binds auto_scc binds = foldM (dsLHsBind auto_scc) [] (bagToList binds)
79 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
81 -> DsM [(Id,CoreExpr)] -- Result
82 dsLHsBind auto_scc rest (L loc bind)
83 = putSrcSpanDs loc $ dsHsBind auto_scc rest bind
86 -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append)
88 -> DsM [(Id,CoreExpr)] -- Result
90 dsHsBind _ rest (VarBind var expr inline_regardless)
91 = do { core_expr <- dsLExpr expr
93 -- Dictionary bindings are always VarBinds,
94 -- so we only need do this here
95 ; core_expr' <- addDictScc var core_expr
96 ; let var' | inline_regardless = var `setIdUnfolding` mkCompulsoryUnfolding core_expr'
99 ; return ((var', core_expr') : rest) }
102 (FunBind { fun_id = L _ fun, fun_matches = matches,
103 fun_co_fn = co_fn, fun_tick = tick, fun_infix = inf })
104 = do { (args, body) <- matchWrapper (FunRhs (idName fun) inf) matches
105 ; body' <- mkOptTickBox tick body
106 ; rhs <- dsCoercion co_fn (return (mkLams args body'))
107 ; return ((fun,rhs) : rest) }
110 (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty })
111 = do { body_expr <- dsGuarded grhss ty
112 ; sel_binds <- mkSelectorBinds pat body_expr
113 ; return (sel_binds ++ rest) }
115 {- Note [Rules and inlining]
116 ~~~~~~~~~~~~~~~~~~~~~~~~~
117 Common special case: no type or dictionary abstraction
118 This is a bit less trivial than you might suppose
119 The naive way woudl be to desguar to something like
120 f_lcl = ...f_lcl... -- The "binds" from AbsBinds
121 M.f = f_lcl -- Generated from "exports"
122 But we don't want that, because if M.f isn't exported,
123 it'll be inlined unconditionally at every call site (its rhs is
124 trivial). That would be ok unless it has RULES, which would
125 thereby be completely lost. Bad, bad, bad.
127 Instead we want to generate
130 Now all is cool. The RULES are attached to M.f (by SimplCore),
131 and f_lcl is rapidly inlined away.
133 This does not happen in the same way to polymorphic binds,
134 because they desugar to
135 M.f = /\a. let f_lcl = ...f_lcl... in f_lcl
136 Although I'm a bit worried about whether full laziness might
137 float the f_lcl binding out and then inline M.f at its call site -}
139 dsHsBind auto_scc rest (AbsBinds [] [] exports binds)
140 = do { core_prs <- ds_lhs_binds NoSccs binds
141 ; let env = mkABEnv exports
142 ar_env = mkArityEnv binds
144 | Just (_, gbl_id, _, prags) <- lookupVarEnv env lcl_id
145 = makeCorePair gbl_id (lookupArity ar_env lcl_id) prags $
146 addAutoScc auto_scc gbl_id rhs
148 | otherwise = (lcl_id, rhs)
150 locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports]
151 -- Note [Rules and inlining]
152 ; return (map do_one core_prs ++ locals' ++ rest) }
153 -- No Rec needed here (contrast the other AbsBinds cases)
154 -- because we can rely on the enclosing dsBind to wrap in Rec
157 {- Note [Abstracting over tyvars only]
158 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
159 When abstracting over type variable only (not dictionaries), we don't really need to
160 built a tuple and select from it, as we do in the general case. Instead we can take
162 AbsBinds [a,b] [ ([a,b], fg, fl, _),
170 fg = /\ab. let B in e1
171 gg = /\b. let a = () in let B in S(e2)
172 h = /\ab. let B in e3
174 where B is the *non-recursive* binding
177 h = h a b -- See (b); note shadowing!
179 Notice (a) g has a different number of type variables to f, so we must
180 use the mkArbitraryType thing to fill in the gaps.
181 We use a type-let to do that.
183 (b) The local variable h isn't in the exports, and rather than
184 clone a fresh copy we simply replace h by (h a b), where
185 the two h's have different types! Shadowing happens here,
186 which looks confusing but works fine.
188 (c) The result is *still* quadratic-sized if there are a lot of
189 small bindings. So if there are more than some small
190 number (10), we filter the binding set B by the free
191 variables of the particular RHS. Tiresome.
193 Why got to this trouble? It's a common case, and it removes the
194 quadratic-sized tuple desugaring. Less clutter, hopefullly faster
195 compilation, especially in a case where there are a *lot* of
200 dsHsBind auto_scc rest (AbsBinds tyvars [] exports binds)
201 | opt_DsMultiTyVar -- This (static) debug flag just lets us
202 -- switch on and off this optimisation to
203 -- see if it has any impact; it is on by default
204 = -- Note [Abstracting over tyvars only]
205 do { core_prs <- ds_lhs_binds NoSccs binds
206 ; arby_env <- mkArbitraryTypeEnv tyvars exports
207 ; let (lg_binds, core_prs') = mapAndUnzip do_one core_prs
208 bndrs = mkVarSet (map fst core_prs)
210 add_lets | core_prs `lengthExceeds` 10 = add_some
211 | otherwise = mkLets lg_binds
212 add_some rhs = mkLets [ NonRec b r | NonRec b r <- lg_binds
213 , b `elemVarSet` fvs] rhs
215 fvs = exprSomeFreeVars (`elemVarSet` bndrs) rhs
217 ar_env = mkArityEnv binds
218 env = mkABEnv exports
221 | Just (id_tvs, gbl_id, _, prags) <- lookupVarEnv env lcl_id
222 = let rhs' = addAutoScc auto_scc gbl_id $
224 mkLets [ NonRec tv (Type (lookupVarEnv_NF arby_env tv))
225 | tv <- tyvars, not (tv `elem` id_tvs)] $
227 in (NonRec lcl_id (mkTyApps (Var gbl_id) (mkTyVarTys id_tvs)),
228 makeCorePair gbl_id (lookupArity ar_env lcl_id) prags rhs')
230 = (NonRec lcl_id (mkTyApps (Var non_exp_gbl_id) (mkTyVarTys tyvars)),
231 (non_exp_gbl_id, mkLams tyvars (add_lets rhs)))
233 non_exp_gbl_id = setIdType lcl_id (mkForAllTys tyvars (idType lcl_id))
235 ; return (core_prs' ++ rest) }
237 -- Another common case: one exported variable
238 -- Non-recursive bindings come through this way
239 -- So do self-recursive bindings, and recursive bindings
240 -- that have been chopped up with type signatures
241 dsHsBind auto_scc rest
242 (AbsBinds all_tyvars dicts [(tyvars, global, local, prags)] binds)
243 = ASSERT( all (`elem` tyvars) all_tyvars )
244 do { core_prs <- ds_lhs_binds NoSccs binds
246 ; let -- Always treat the binds as recursive, because the typechecker
247 -- makes rather mixed-up dictionary bindings
248 core_bind = Rec core_prs
249 inl_arity = lookupArity (mkArityEnv binds) local
251 ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global
252 local inl_arity core_bind) prags
254 ; let (spec_binds, rules) = unzip (catMaybes mb_specs)
255 global' = addIdSpecialisations global rules
256 rhs = addAutoScc auto_scc global $
257 mkLams tyvars $ mkLams dicts $ Let core_bind (Var local)
258 main_bind = makeCorePair global' (inl_arity + length dicts) prags rhs
260 ; return (main_bind : spec_binds ++ rest) }
262 dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds)
263 = do { core_prs <- ds_lhs_binds NoSccs binds
264 ; let env = mkABEnv exports
265 ar_env = mkArityEnv binds
266 do_one (lcl_id,rhs) | Just (_, gbl_id, _, _prags) <- lookupVarEnv env lcl_id
267 = (lcl_id, addAutoScc auto_scc gbl_id rhs)
268 | otherwise = (lcl_id,rhs)
270 -- Rec because of mixed-up dictionary bindings
271 core_bind = Rec (map do_one core_prs)
273 tup_expr = mkBigCoreVarTup locals
274 tup_ty = exprType tup_expr
275 poly_tup_expr = mkLams all_tyvars $ mkLams dicts $
276 Let core_bind tup_expr
277 locals = [local | (_, _, local, _) <- exports]
278 local_tys = map idType locals
280 inl_prags :: [(Id, SrcSpan)]
281 inl_prags = [(id, loc) | (_, id, _, prags) <- exports
282 , L loc (InlinePrag {}) <- prags ]
284 ; mapM_ discardedInlineWarning inl_prags
286 ; poly_tup_id <- newSysLocalDs (exprType poly_tup_expr)
288 ; let dict_args = map Var dicts
290 mk_bind ((tyvars, global, local, prags), n) -- locals !! n == local
291 = -- Need to make fresh locals to bind in the selector, because
292 -- some of the tyvars will be bound to 'Any'
293 do { ty_args <- mapM mk_ty_arg all_tyvars
294 ; let substitute = substTyWith all_tyvars ty_args
295 ; locals' <- newSysLocalsDs (map substitute local_tys)
296 ; tup_id <- newSysLocalDs (substitute tup_ty)
297 ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global local
298 (lookupArity ar_env local) core_bind)
300 ; let (spec_binds, rules) = unzip (catMaybes mb_specs)
301 global' = addIdSpecialisations global rules
302 rhs = mkLams tyvars $ mkLams dicts $
303 mkTupleSelector locals' (locals' !! n) tup_id $
304 mkApps (mkTyApps (Var poly_tup_id) ty_args) dict_args
305 ; return ((global', rhs) : spec_binds) }
308 | all_tyvar `elem` tyvars = return (mkTyVarTy all_tyvar)
309 | otherwise = dsMkArbitraryType all_tyvar
311 ; export_binds_s <- mapM mk_bind (exports `zip` [0..])
312 -- Don't scc (auto-)annotate the tuple itself.
314 ; return ((poly_tup_id, poly_tup_expr) :
315 (concat export_binds_s ++ rest)) }
317 ------------------------
318 makeCorePair :: Id-> Arity -> [LPrag] -> CoreExpr -> (Id, CoreExpr)
319 makeCorePair gbl_id arity prags rhs
320 = (addInline gbl_id arity rhs prags, rhs)
322 ------------------------
323 discardedInlineWarning :: (Id, SrcSpan) -> DsM ()
324 discardedInlineWarning (id, loc)
326 warnDs $ sep [ ptext (sLit "Discarding INLINE pragma for") <+> ppr id
327 , ptext (sLit "because it is bound by a pattern, or a mutual recursion") ]
329 ------------------------
330 type AbsBindEnv = VarEnv ([TyVar], Id, Id, [LPrag])
331 -- Maps the "lcl_id" for an AbsBind to
332 -- its "gbl_id" and associated pragmas, if any
334 mkABEnv :: [([TyVar], Id, Id, [LPrag])] -> AbsBindEnv
335 -- Takes the exports of a AbsBinds, and returns a mapping
336 -- lcl_id -> (tyvars, gbl_id, lcl_id, prags)
337 mkABEnv exports = mkVarEnv [ (lcl_id, export) | export@(_, _, lcl_id, _) <- exports]
339 mkArityEnv :: LHsBinds Id -> IdEnv Arity
340 -- Maps a local to the arity of its definition
341 mkArityEnv binds = mkVarEnv (mapCatMaybes get_arity (bagToList binds))
343 get_arity (L _ (FunBind { fun_id = id, fun_matches = ms })) = Just (unLoc id, matchGroupArity ms)
344 get_arity _ = Nothing
346 lookupArity :: IdEnv Arity -> Id -> Arity
347 lookupArity ar_env id = lookupVarEnv ar_env id `orElse` 0
349 addInline :: Id -> Arity -> CoreExpr -> [LPrag] -> Id
350 addInline id arity rhs prags
351 = case [inl | L _ (InlinePrag inl) <- prags] of
353 (inl_spec : _) -> addInlineToId id arity rhs inl_spec
355 addInlineToId :: Id -> Arity -> CoreExpr -> InlineSpec -> Id
356 addInlineToId id inl_arity rhs (Inline phase is_inline)
357 = id `setInlinePragma` phase
358 `setIdUnfolding` inline_rule
360 inline_rule | is_inline = mkInlineRule rhs inl_arity
361 | otherwise = noUnfolding
363 ------------------------
364 dsSpec :: [TyVar] -> [DictId] -> [TyVar]
365 -> Id -> Id -> Arity -- Global, local, arity of local
367 -> DsM (Maybe ((Id,CoreExpr), -- Binding for specialised Id
368 CoreRule)) -- Rule for the Global Id
371 -- f :: (Eq a, Ix b) => a -> b -> b
372 -- {-# SPECIALISE f :: Ix b => Int -> b -> b #-}
374 -- AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds
376 -- SpecPrag (/\b.\(d:Ix b). f Int b dInt d)
377 -- (forall b. Ix b => Int -> b -> b)
379 -- Rule: forall b,(d:Ix b). f Int b dInt d = f_spec b d
381 -- Spec bind: f_spec = Let f = /\ab \(d1:Eq a)(d2:Ix b). let binds in f_mono
382 -- /\b.\(d:Ix b). in f Int b dInt d
383 -- The idea is that f occurs just once, so it'll be
384 -- inlined and specialised
386 -- Given SpecPrag (/\as.\ds. f es) t, we have
387 -- the defn f_spec as ds = let-nonrec f = /\fas\fds. let f_mono = <f-rhs> in f_mono
389 -- and the RULE forall as, ds. f es = f_spec as ds
391 -- It is *possible* that 'es' does not mention all of the dictionaries 'ds'
392 -- (a bit silly, because then the
393 dsSpec _ _ _ _ _ _ _ (L _ (InlinePrag {}))
396 dsSpec all_tvs dicts tvs poly_id mono_id inl_arity mono_bind
397 (L loc (SpecPrag spec_expr spec_ty inl))
399 do { let poly_name = idName poly_id
400 ; spec_name <- newLocalName poly_name
401 ; ds_spec_expr <- dsExpr spec_expr
402 ; case (decomposeRuleLhs ds_spec_expr) of {
403 Nothing -> do { warnDs decomp_msg; return Nothing } ;
405 Just (bndrs, _fn, args) ->
407 -- Check for dead binders: Note [Unused spec binders]
408 case filter isDeadBinder bndrs of {
409 bs | not (null bs) -> do { warnDs (dead_msg bs); return Nothing }
412 { f_body <- fix_up (Let mono_bind (Var mono_id))
414 ; let local_poly = setIdNotExported poly_id
415 -- Very important to make the 'f' non-exported,
416 -- else it won't be inlined!
417 spec_id = mkLocalId spec_name spec_ty
418 spec_id1 = addInlineToId spec_id (inl_arity + count isDictId bndrs)
420 spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr
421 poly_f_body = mkLams (tvs ++ dicts) f_body
423 extra_dict_bndrs = [localiseId d -- See Note [Constant rule dicts]
424 | d <- varSetElems (exprFreeVars ds_spec_expr)
426 -- Note [Const rule dicts]
428 rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
429 AlwaysActive poly_name
430 (extra_dict_bndrs ++ bndrs) args
431 (mkVarApps (Var spec_id) bndrs)
432 ; return (Just ((spec_id1, spec_rhs), rule))
435 -- Bind to Any any of all_ptvs that aren't
436 -- relevant for this particular function
437 fix_up body | null void_tvs = return body
438 | otherwise = do { void_tys <- mapM dsMkArbitraryType void_tvs
439 ; return (mkTyApps (mkLams void_tvs body) void_tys) }
441 void_tvs = all_tvs \\ tvs
443 dead_msg bs = vcat [ sep [ptext (sLit "Useless constraint") <> plural bs
444 <+> ptext (sLit "in specialied type:"),
445 nest 2 (pprTheta (map get_pred bs))]
446 , ptext (sLit "SPECIALISE pragma ignored")]
447 get_pred b = ASSERT( isId b ) expectJust "dsSpec" (tcSplitPredTy_maybe (idType b))
449 decomp_msg = hang (ptext (sLit "Specialisation too complicated to desugar; ignored"))
453 mkArbitraryTypeEnv :: [TyVar] -> [([TyVar], a, b, c)] -> DsM (TyVarEnv Type)
454 -- If any of the tyvars is missing from any of the lists in
455 -- the second arg, return a binding in the result
456 mkArbitraryTypeEnv tyvars exports
457 = go emptyVarEnv exports
459 go env [] = return env
460 go env ((ltvs, _, _, _) : exports)
461 = do { env' <- foldlM extend env [tv | tv <- tyvars
462 , not (tv `elem` ltvs)
463 , not (tv `elemVarEnv` env)]
466 extend env tv = do { ty <- dsMkArbitraryType tv
467 ; return (extendVarEnv env tv ty) }
470 dsMkArbitraryType :: TcTyVar -> DsM Type
471 dsMkArbitraryType tv = mkArbitraryType warn tv
473 warn span msg = putSrcSpanDs span (warnDs msg)
476 Note [Unused spec binders]
477 ~~~~~~~~~~~~~~~~~~~~~~~~~~
480 {-# SPECIALISE f :: Eq a => a -> a #-}
481 It's true that this *is* a more specialised type, but the rule
482 we get is something like this:
485 Note that the rule is bogus, becuase it mentions a 'd' that is
486 not bound on the LHS! But it's a silly specialisation anyway, becuase
487 the constraint is unused. We could bind 'd' to (error "unused")
488 but it seems better to reject the program because it's almost certainly
489 a mistake. That's what the isDeadBinder call detects.
491 Note [Const rule dicts]
492 ~~~~~~~~~~~~~~~~~~~~~~~
493 When the LHS of a specialisation rule, (/\as\ds. f es) has a free dict,
494 which is presumably in scope at the function definition site, we can quantify
495 over it too. *Any* dict with that type will do.
497 So for example when you have
500 {-# SPECIALISE f :: Int -> Int #-}
502 Then we get the SpecPrag
503 SpecPrag (f Int dInt) Int
505 And from that we want the rule
507 RULE forall dInt. f Int dInt = f_spec
508 f_spec = let f = <rhs> in f Int dInt
510 But be careful! That dInt might be GHC.Base.$fOrdInt, which is an External
511 Name, and you can't bind them in a lambda or forall without getting things
512 confused. Hence the use of 'localiseId' to make it Internal.
515 %************************************************************************
517 \subsection{Adding inline pragmas}
519 %************************************************************************
522 decomposeRuleLhs :: CoreExpr -> Maybe ([Var], Id, [CoreExpr])
523 -- Take apart the LHS of a RULE. It's suuposed to look like
524 -- /\a. f a Int dOrdInt
525 -- or /\a.\d:Ord a. let { dl::Ord [a] = dOrdList a d } in f [a] dl
526 -- That is, the RULE binders are lambda-bound
527 -- Returns Nothing if the LHS isn't of the expected shape
529 = case (decomp emptyVarEnv body) of
531 Just (fn, args) -> Just (bndrs, fn, args)
533 occ_lhs = occurAnalyseExpr lhs
534 -- The occurrence-analysis does two things
535 -- (a) identifies unused binders: Note [Unused spec binders]
536 -- (b) sorts dict bindings into NonRecs
537 -- so they can be inlined by 'decomp'
538 (bndrs, body) = collectBinders occ_lhs
540 -- Substitute dicts in the LHS args, so that there
541 -- aren't any lets getting in the way
542 -- Note that we substitute the function too; we might have this as
543 -- a LHS: let f71 = M.f Int in f71
544 decomp env (Let (NonRec dict rhs) body)
545 = decomp (extendVarEnv env dict (simpleSubst env rhs)) body
547 = case collectArgs (simpleSubst env body) of
548 (Var fn, args) -> Just (fn, args)
551 simpleSubst :: IdEnv CoreExpr -> CoreExpr -> CoreExpr
552 -- Similar to CoreSubst.substExpr, except that
553 -- (a) Takes no account of capture; at this point there is no shadowing
554 -- (b) Can have a GlobalId (imported) in its domain
555 -- (c) Ids only; no types are substituted
556 -- (d) Does not insist (as does CoreSubst.lookupIdSubst) that the
557 -- in-scope set mentions all LocalIds mentioned in the argument of the subst
559 -- (b) and (d) are the reasons we can't use CoreSubst
561 -- (I had a note that (b) is "no longer relevant", and indeed it doesn't
562 -- look relevant here. Perhaps there was another caller of simpleSubst.)
564 simpleSubst subst expr
567 go (Var v) = lookupVarEnv subst v `orElse` Var v
568 go (Cast e co) = Cast (go e) co
569 go (Type ty) = Type ty
570 go (Lit lit) = Lit lit
571 go (App fun arg) = App (go fun) (go arg)
572 go (Note note e) = Note note (go e)
573 go (Lam bndr body) = Lam bndr (go body)
574 go (Let (NonRec bndr rhs) body) = Let (NonRec bndr (go rhs)) (go body)
575 go (Let (Rec pairs) body) = Let (Rec (mapSnd go pairs)) (go body)
576 go (Case scrut bndr ty alts) = Case (go scrut) bndr ty
577 [(c,bs,go r) | (c,bs,r) <- alts]
581 %************************************************************************
583 \subsection[addAutoScc]{Adding automatic sccs}
585 %************************************************************************
588 data AutoScc = NoSccs
589 | AddSccs Module (Id -> Bool)
590 -- The (Id->Bool) says which Ids to add SCCs to
592 addAutoScc :: AutoScc
595 -> CoreExpr -- Scc'd Rhs
597 addAutoScc NoSccs _ rhs
599 addAutoScc (AddSccs mod add_scc) id rhs
600 | add_scc id = mkSCC (mkAutoCC id mod NotCafCC) rhs
604 If profiling and dealing with a dict binding,
605 wrap the dict in @_scc_ DICT <dict>@:
608 addDictScc :: Id -> CoreExpr -> DsM CoreExpr
609 addDictScc _ rhs = return rhs
611 {- DISABLED for now (need to somehow make up a name for the scc) -- SDM
612 | not ( opt_SccProfilingOn && opt_AutoSccsOnDicts)
613 || not (isDictId var)
614 = return rhs -- That's easy: do nothing
617 = do (mod, grp) <- getModuleAndGroupDs
618 -- ToDo: do -dicts-all flag (mark dict things with individual CCs)
619 return (Note (SCC (mkAllDictsCC mod grp False)) rhs)
624 %************************************************************************
628 %************************************************************************
632 dsCoercion :: HsWrapper -> DsM CoreExpr -> DsM CoreExpr
633 dsCoercion WpHole thing_inside = thing_inside
634 dsCoercion (WpCompose c1 c2) thing_inside = dsCoercion c1 (dsCoercion c2 thing_inside)
635 dsCoercion (WpCast co) thing_inside = do { expr <- thing_inside
636 ; return (Cast expr co) }
637 dsCoercion (WpLam id) thing_inside = do { expr <- thing_inside
638 ; return (Lam id expr) }
639 dsCoercion (WpTyLam tv) thing_inside = do { expr <- thing_inside
640 ; return (Lam tv expr) }
641 dsCoercion (WpApp v) thing_inside
642 | isTyVar v = do { expr <- thing_inside
643 {- Probably a coercion var -} ; return (App expr (Type (mkTyVarTy v))) }
644 | otherwise = do { expr <- thing_inside
645 {- An Id -} ; return (App expr (Var v)) }
646 dsCoercion (WpTyApp ty) thing_inside = do { expr <- thing_inside
647 ; return (App expr (Type ty)) }
648 dsCoercion (WpLet bs) thing_inside = do { prs <- dsLHsBinds bs
649 ; expr <- thing_inside
650 ; return (Let (Rec prs) expr) }