2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreUtils]{Utility functions on @Core@ syntax}
9 InScopeSet, emptyInScopeSet, mkInScopeSet,
10 extendInScopeSet, extendInScopeSetList,
11 lookupInScope, elemInScopeSet, uniqAway,
15 Subst, TyVarSubst, IdSubst,
16 emptySubst, mkSubst, substEnv, substInScope,
17 lookupSubst, lookupIdSubst, isEmptySubst, extendSubst, extendSubstList,
18 zapSubstEnv, setSubstEnv,
20 extendInScope, extendInScopeList, extendNewInScope, extendNewInScopeList,
21 isInScope, modifyInScope,
23 bindSubst, unBindSubst, bindSubstList, unBindSubstList,
26 substBndr, substBndrs, substTyVar, substId, substIds,
27 substAndCloneId, substAndCloneIds,
30 mkTyVarSubst, mkTopTyVarSubst,
31 substTy, substClasses, substTheta,
34 substExpr, substIdInfo
37 #include "HsVersions.h"
39 import CmdLineOpts ( opt_PprStyle_Debug )
40 import CoreSyn ( Expr(..), Bind(..), Note(..), CoreExpr, CoreBndr,
41 CoreRules(..), CoreRule(..),
42 emptyCoreRules, isEmptyCoreRules, seqRules
44 import CoreFVs ( exprFreeVars, mustHaveLocalBinding )
45 import TypeRep ( Type(..), TyNote(..),
47 import Type ( ThetaType, PredType(..), ClassContext,
48 tyVarsOfType, tyVarsOfTypes, mkAppTy
52 import Var ( setVarUnique, isId )
53 import Id ( idType, setIdType, idOccInfo, zapFragileIdInfo )
54 import IdInfo ( IdInfo, isFragileOcc,
55 specInfo, setSpecInfo,
56 WorkerInfo(..), workerExists, workerInfo, setWorkerInfo, WorkerInfo
58 import Unique ( Uniquable(..), deriveUnique )
59 import UniqSet ( elemUniqSet_Directly )
60 import UniqSupply ( UniqSupply, uniqFromSupply, splitUniqSupply )
61 import Var ( Var, Id, TyVar, isTyVar )
63 import PprCore () -- Instances
64 import Util ( mapAccumL, foldl2, seqList, ($!) )
68 %************************************************************************
70 \subsection{The in-scope set}
72 %************************************************************************
75 data InScopeSet = InScope (VarEnv Var) Int#
76 -- The Int# is a kind of hash-value used by uniqAway
77 -- For example, it might be the size of the set
78 -- INVARIANT: it's not zero; we use it as a multiplier in uniqAway
80 emptyInScopeSet :: InScopeSet
81 emptyInScopeSet = InScope emptyVarSet 1#
83 mkInScopeSet :: VarEnv Var -> InScopeSet
84 mkInScopeSet in_scope = InScope in_scope 1#
86 extendInScopeSet :: InScopeSet -> Var -> InScopeSet
87 extendInScopeSet (InScope in_scope n) v = InScope (extendVarEnv in_scope v v) (n +# 1#)
89 extendInScopeSetList :: InScopeSet -> [Var] -> InScopeSet
90 extendInScopeSetList (InScope in_scope n) vs = InScope (foldl (\s v -> extendVarEnv s v v) in_scope vs)
91 (case length vs of { I# l -> n +# l })
93 modifyInScopeSet :: InScopeSet -> Var -> Var -> InScopeSet
94 -- Exploit the fact that the in-scope "set" is really a map
95 -- Make old_v map to new_v
96 modifyInScopeSet (InScope in_scope n) old_v new_v = InScope (extendVarEnv in_scope old_v new_v) (n +# 1#)
98 delInScopeSet :: InScopeSet -> Var -> InScopeSet
99 delInScopeSet (InScope in_scope n) v = InScope (in_scope `delVarEnv` v) n
101 elemInScopeSet :: Var -> InScopeSet -> Bool
102 elemInScopeSet v (InScope in_scope n) = v `elemVarEnv` in_scope
104 lookupInScope :: InScopeSet -> Var -> Var
105 -- It's important to look for a fixed point
106 -- When we see (case x of y { I# v -> ... })
107 -- we add [x -> y] to the in-scope set (Simplify.simplCaseBinder).
108 -- When we lookup up an occurrence of x, we map to y, but then
109 -- we want to look up y in case it has acquired more evaluation information by now.
110 lookupInScope (InScope in_scope n) v
113 go v = case lookupVarEnv in_scope v of
114 Just v' | v == v' -> v' -- Reached a fixed point
116 Nothing -> WARN( mustHaveLocalBinding v, ppr v )
121 uniqAway :: InScopeSet -> Var -> Var
122 -- (uniqAway in_scope v) finds a unique that is not used in the
123 -- in-scope set, and gives that to v. It starts with v's current unique, of course,
124 -- in the hope that it won't have to change it, nad thereafter uses a combination
125 -- of that and the hash-code found in the in-scope set
126 uniqAway (InScope set n) var
127 | not (var `elemVarSet` set) = var -- Nothing to do
130 orig_unique = getUnique var
134 = pprPanic "uniqAway loop:" (ppr (I# k) <+> text "tries" <+> ppr var <+> int (I# n))
136 | uniq `elemUniqSet_Directly` set = try (k +# 1#)
138 | opt_PprStyle_Debug && k ># 3#
139 = pprTrace "uniqAway:" (ppr (I# k) <+> text "tries" <+> ppr var <+> int (I# n))
140 setVarUnique var uniq
142 | otherwise = setVarUnique var uniq
144 uniq = deriveUnique orig_unique (I# (n *# k))
148 %************************************************************************
150 \subsection{Substitutions}
152 %************************************************************************
155 data Subst = Subst InScopeSet -- In scope
156 SubstEnv -- Substitution itself
157 -- INVARIANT 1: The (domain of the) in-scope set is a superset
158 -- of the free vars of the range of the substitution
159 -- that might possibly clash with locally-bound variables
160 -- in the thing being substituted in.
161 -- This is what lets us deal with name capture properly
162 -- It's a hard invariant to check...
163 -- There are various ways of causing it to happen:
164 -- - arrange that the in-scope set really is all the things in scope
165 -- - arrange that it's the free vars of the range of the substitution
166 -- - make it empty because all the free vars of the subst are fresh,
167 -- and hence can't possibly clash.a
169 -- INVARIANT 2: No variable is both in scope and in the domain of the substitution
170 -- Equivalently, the substitution is idempotent
176 The general plan about the substitution and in-scope set for Ids is as follows
178 * substId always adds new_id to the in-scope set.
179 new_id has a correctly-substituted type, but all its fragile IdInfo has been zapped.
180 That is added back in later. So new_id is the minimal thing it's
181 correct to substitute.
183 * substId adds a binding (DoneVar new_id occ) to the substitution if
184 EITHER the Id's unique has changed
185 OR the Id has interesting occurrence information
186 So in effect you can only get to interesting occurrence information
187 by looking up the *old* Id; it's not really attached to the new id
190 Note, though that the substitution isn't necessarily extended
191 if the type changes. Why not? Because of the next point:
193 * We *always, always* finish by looking up in the in-scope set
194 any variable that doesn't get a DoneEx or DoneVar hit in the substitution.
195 Reason: so that we never finish up with a "old" Id in the result.
196 An old Id might point to an old unfolding and so on... which gives a space leak.
198 [The DoneEx and DoneVar hits map to "new" stuff.]
200 * It follows that substExpr must not do a no-op if the substitution is empty.
201 substType is free to do so, however.
203 * When we come to a let-binding (say) we generate new IdInfo, including an
204 unfolding, attach it to the binder, and add this newly adorned binder to
205 the in-scope set. So all subsequent occurrences of the binder will get mapped
206 to the full-adorned binder, which is also the one put in the binding site.
208 * The in-scope "set" usually maps x->x; we use it simply for its domain.
209 But sometimes we have two in-scope Ids that are synomyms, and should
210 map to the same target: x->x, y->x. Notably:
212 That's why the "set" is actually a VarEnv Var
216 isEmptySubst :: Subst -> Bool
217 isEmptySubst (Subst _ env) = isEmptySubstEnv env
220 emptySubst = Subst emptyInScopeSet emptySubstEnv
222 mkSubst :: InScopeSet -> SubstEnv -> Subst
223 mkSubst in_scope env = Subst in_scope env
225 substEnv :: Subst -> SubstEnv
226 substEnv (Subst _ env) = env
228 substInScope :: Subst -> InScopeSet
229 substInScope (Subst in_scope _) = in_scope
231 zapSubstEnv :: Subst -> Subst
232 zapSubstEnv (Subst in_scope env) = Subst in_scope emptySubstEnv
234 extendSubst :: Subst -> Var -> SubstResult -> Subst
235 extendSubst (Subst in_scope env) v r = Subst in_scope (extendSubstEnv env v r)
237 extendSubstList :: Subst -> [Var] -> [SubstResult] -> Subst
238 extendSubstList (Subst in_scope env) v r = Subst in_scope (extendSubstEnvList env v r)
240 lookupSubst :: Subst -> Var -> Maybe SubstResult
241 lookupSubst (Subst _ env) v = lookupSubstEnv env v
243 lookupIdSubst :: Subst -> Id -> SubstResult
244 -- Does the lookup in the in-scope set too
245 lookupIdSubst (Subst in_scope env) v
246 = case lookupSubstEnv env v of
247 Just (DoneId v' occ) -> DoneId (lookupInScope in_scope v') occ
249 Nothing -> DoneId v' (idOccInfo v')
250 -- We don't use DoneId for LoopBreakers, so the idOccInfo is
251 -- very important! If isFragileOcc returned True for
252 -- loop breakers we could avoid this call, but at the expense
253 -- of adding more to the substitution, and building new Ids
254 -- in substId a bit more often than really necessary
256 v' = lookupInScope in_scope v
258 isInScope :: Var -> Subst -> Bool
259 isInScope v (Subst in_scope _) = v `elemInScopeSet` in_scope
261 modifyInScope :: Subst -> Var -> Var -> Subst
262 modifyInScope (Subst in_scope env) old_v new_v = Subst (modifyInScopeSet in_scope old_v new_v) env
263 -- make old_v map to new_v
265 extendInScope :: Subst -> Var -> Subst
266 -- Add a new variable as in-scope
267 -- Remember to delete any existing binding in the substitution!
268 extendInScope (Subst in_scope env) v = Subst (in_scope `extendInScopeSet` v)
269 (env `delSubstEnv` v)
271 extendInScopeList :: Subst -> [Var] -> Subst
272 extendInScopeList (Subst in_scope env) vs = Subst (extendInScopeSetList in_scope vs)
273 (delSubstEnvList env vs)
275 -- The "New" variants are guaranteed to be adding freshly-allocated variables
276 -- It's not clear that the gain (not needing to delete it from the substitution)
277 -- is worth the extra proof obligation
278 extendNewInScope :: Subst -> Var -> Subst
279 extendNewInScope (Subst in_scope env) v = Subst (in_scope `extendInScopeSet` v) env
281 extendNewInScopeList :: Subst -> [Var] -> Subst
282 extendNewInScopeList (Subst in_scope env) vs = Subst (in_scope `extendInScopeSetList` vs) env
284 -------------------------------
285 bindSubst :: Subst -> Var -> Var -> Subst
286 -- Extend with a substitution, v1 -> Var v2
287 -- and extend the in-scopes with v2
288 bindSubst (Subst in_scope env) old_bndr new_bndr
289 = Subst (in_scope `extendInScopeSet` new_bndr)
290 (extendSubstEnv env old_bndr subst_result)
292 subst_result | isId old_bndr = DoneEx (Var new_bndr)
293 | otherwise = DoneTy (TyVarTy new_bndr)
295 unBindSubst :: Subst -> Var -> Var -> Subst
296 -- Reverse the effect of bindSubst
297 -- If old_bndr was already in the substitution, this doesn't quite work
298 unBindSubst (Subst in_scope env) old_bndr new_bndr
299 = Subst (in_scope `delInScopeSet` new_bndr) (delSubstEnv env old_bndr)
301 -- And the "List" forms
302 bindSubstList :: Subst -> [Var] -> [Var] -> Subst
303 bindSubstList subst old_bndrs new_bndrs
304 = foldl2 bindSubst subst old_bndrs new_bndrs
306 unBindSubstList :: Subst -> [Var] -> [Var] -> Subst
307 unBindSubstList subst old_bndrs new_bndrs
308 = foldl2 unBindSubst subst old_bndrs new_bndrs
311 -------------------------------
312 setInScope :: Subst -- Take env part from here
315 setInScope (Subst in_scope1 env1) in_scope2
316 = Subst in_scope2 env1
318 setSubstEnv :: Subst -- Take in-scope part from here
319 -> SubstEnv -- ... and env part from here
321 setSubstEnv (Subst in_scope1 _) env2 = Subst in_scope1 env2
325 %************************************************************************
327 \subsection{Type substitution}
329 %************************************************************************
332 type TyVarSubst = Subst -- TyVarSubst are expected to have range elements
333 -- (We could have a variant of Subst, but it doesn't seem worth it.)
335 -- mkTyVarSubst generates the in-scope set from
336 -- the types given; but it's just a thunk so with a bit of luck
337 -- it'll never be evaluated
338 mkTyVarSubst :: [TyVar] -> [Type] -> Subst
339 mkTyVarSubst tyvars tys = Subst (mkInScopeSet (tyVarsOfTypes tys)) (zip_ty_env tyvars tys emptySubstEnv)
341 -- mkTopTyVarSubst is called when doing top-level substitutions.
342 -- Here we expect that the free vars of the range of the
343 -- substitution will be empty.
344 mkTopTyVarSubst :: [TyVar] -> [Type] -> Subst
345 mkTopTyVarSubst tyvars tys = Subst emptyInScopeSet (zip_ty_env tyvars tys emptySubstEnv)
347 zip_ty_env [] [] env = env
348 zip_ty_env (tv:tvs) (ty:tys) env = zip_ty_env tvs tys (extendSubstEnv env tv (DoneTy ty))
351 substTy works with general Substs, so that it can be called from substExpr too.
354 substTy :: Subst -> Type -> Type
355 substTy subst ty | isEmptySubst subst = ty
356 | otherwise = subst_ty subst ty
358 substClasses :: TyVarSubst -> ClassContext -> ClassContext
359 substClasses subst theta
360 | isEmptySubst subst = theta
361 | otherwise = [(clas, map (subst_ty subst) tys) | (clas, tys) <- theta]
363 substTheta :: TyVarSubst -> ThetaType -> ThetaType
364 substTheta subst theta
365 | isEmptySubst subst = theta
366 | otherwise = map (substPred subst) theta
368 substPred :: TyVarSubst -> PredType -> PredType
369 substPred subst (Class clas tys) = Class clas (map (subst_ty subst) tys)
370 substPred subst (IParam n ty) = IParam n (subst_ty subst ty)
375 go (TyConApp tc tys) = let args = map go tys
376 in args `seqList` TyConApp tc args
377 go (NoteTy (SynNote ty1) ty2) = NoteTy (SynNote $! (go ty1)) $! (go ty2)
378 go (NoteTy (FTVNote _) ty2) = go ty2 -- Discard the free tyvar note
379 go (NoteTy (UsgNote usg) ty2) = (NoteTy $! UsgNote usg) $! go ty2 -- Keep usage annot
380 go (NoteTy (UsgForAll uv) ty2) = (NoteTy $! UsgForAll uv) $! go ty2 -- Keep uvar bdr
381 go (NoteTy (IPNote nm) ty2) = (NoteTy $! IPNote nm) $! go ty2 -- Keep ip note
383 go (FunTy arg res) = (FunTy $! (go arg)) $! (go res)
384 go (AppTy fun arg) = mkAppTy (go fun) $! (go arg)
385 go ty@(TyVarTy tv) = case (lookupSubst subst tv) of
387 Just (DoneTy ty') -> ty'
389 go (ForAllTy tv ty) = case substTyVar subst tv of
390 (subst', tv') -> ForAllTy tv' $! (subst_ty subst' ty)
393 Here is where we invent a new binder if necessary.
396 substTyVar :: Subst -> TyVar -> (Subst, TyVar)
397 substTyVar subst@(Subst in_scope env) old_var
398 | old_var == new_var -- No need to clone
399 -- But we *must* zap any current substitution for the variable.
401 -- (\x.e) with id_subst = [x |-> e']
402 -- Here we must simply zap the substitution for x
404 -- The new_id isn't cloned, but it may have a different type
405 -- etc, so we must return it, not the old id
406 = (Subst (in_scope `extendInScopeSet` new_var)
407 (delSubstEnv env old_var),
410 | otherwise -- The new binder is in scope so
411 -- we'd better rename it away from the in-scope variables
412 -- Extending the substitution to do this renaming also
413 -- has the (correct) effect of discarding any existing
414 -- substitution for that variable
415 = (Subst (in_scope `extendInScopeSet` new_var)
416 (extendSubstEnv env old_var (DoneTy (TyVarTy new_var))),
419 new_var = uniqAway in_scope old_var
420 -- The uniqAway part makes sure the new variable is not already in scope
424 %************************************************************************
426 \section{Expression substitution}
428 %************************************************************************
430 This expression substituter deals correctly with name capture.
432 BUT NOTE that substExpr silently discards the
435 IdInfo attached to any binders in the expression. It's quite
436 tricky to do them 'right' in the case of mutually recursive bindings,
437 and so far has proved unnecessary.
440 substExpr :: Subst -> CoreExpr -> CoreExpr
442 -- NB: we do not do a no-op when the substitution is empty,
443 -- because we always want to substitute the variables in the
444 -- in-scope set for their occurrences. Why?
445 -- (a) because they may contain more information
446 -- (b) because leaving an un-substituted Id might cause
447 -- a space leak (its unfolding might point to an old version
448 -- of its right hand side).
452 go (Var v) = -- See the notes at the top, with the Subst data type declaration
453 case lookupIdSubst subst v of
455 ContEx env' e' -> substExpr (setSubstEnv subst env') e'
459 go (Type ty) = Type (go_ty ty)
460 go (Lit lit) = Lit lit
461 go (App fun arg) = App (go fun) (go arg)
462 go (Note note e) = Note (go_note note) (go e)
464 go (Lam bndr body) = Lam bndr' (substExpr subst' body)
466 (subst', bndr') = substBndr subst bndr
468 go (Let (NonRec bndr rhs) body) = Let (NonRec bndr' (go rhs)) (substExpr subst' body)
470 (subst', bndr') = substBndr subst bndr
472 go (Let (Rec pairs) body) = Let (Rec pairs') (substExpr subst' body)
474 (subst', bndrs') = substBndrs subst (map fst pairs)
475 pairs' = bndrs' `zip` rhss'
476 rhss' = map (substExpr subst' . snd) pairs
478 go (Case scrut bndr alts) = Case (go scrut) bndr' (map (go_alt subst') alts)
480 (subst', bndr') = substBndr subst bndr
482 go_alt subst (con, bndrs, rhs) = (con, bndrs', substExpr subst' rhs)
484 (subst', bndrs') = substBndrs subst bndrs
486 go_note (Coerce ty1 ty2) = Coerce (go_ty ty1) (go_ty ty2)
489 go_ty ty = substTy subst ty
493 Substituting in binders is a rather tricky part of the whole compiler.
495 When we hit a binder we may need to
496 (a) apply the the type envt (if non-empty) to its type
497 (c) give it a new unique to avoid name clashes
500 substBndr :: Subst -> Var -> (Subst, Var)
502 | isTyVar bndr = substTyVar subst bndr
503 | otherwise = substId subst bndr
505 substBndrs :: Subst -> [Var] -> (Subst, [Var])
506 substBndrs subst bndrs = mapAccumL substBndr subst bndrs
509 substIds :: Subst -> [Id] -> (Subst, [Id])
510 substIds subst bndrs = mapAccumL substId subst bndrs
512 substId :: Subst -> Id -> (Subst, Id)
513 -- Returns an Id with empty IdInfo
514 -- See the notes with the Subst data type decl at the
515 -- top of this module
517 substId subst@(Subst in_scope env) old_id
518 = (Subst (in_scope `extendInScopeSet` new_id) new_env, new_id)
520 id_ty = idType old_id
521 occ_info = idOccInfo old_id
523 -- id1 has its type zapped
524 id1 | noTypeSubst env
525 || isEmptyVarSet (tyVarsOfType id_ty) = old_id
526 -- The tyVarsOfType is cheaper than it looks
527 -- because we cache the free tyvars of the type
528 -- in a Note in the id's type itself
529 | otherwise = setIdType old_id (substTy subst id_ty)
531 -- id2 has its IdInfo zapped
532 id2 = zapFragileIdInfo id1
534 -- new_id is cloned if necessary
535 new_id = uniqAway in_scope id2
537 -- Extend the substitution if the unique has changed,
538 -- or there's some useful occurrence information
539 -- See the notes with substTyVar for the delSubstEnv
540 new_env | new_id /= old_id || isFragileOcc occ_info
541 = extendSubstEnv env old_id (DoneId new_id occ_info)
543 = delSubstEnv env old_id
546 Now a variant that unconditionally allocates a new unique.
549 substAndCloneIds :: Subst -> UniqSupply -> [Id] -> (Subst, UniqSupply, [Id])
550 substAndCloneIds subst us [] = (subst, us, [])
551 substAndCloneIds subst us (b:bs) = case substAndCloneId subst us b of { (subst1, us1, b') ->
552 case substAndCloneIds subst1 us1 bs of { (subst2, us2, bs') ->
553 (subst2, us2, (b':bs')) }}
555 substAndCloneId :: Subst -> UniqSupply -> Id -> (Subst, UniqSupply, Id)
556 substAndCloneId subst@(Subst in_scope env) us old_id
557 = (Subst (in_scope `extendInScopeSet` new_id)
558 (extendSubstEnv env old_id (DoneEx (Var new_id))),
562 id_ty = idType old_id
563 id1 | noTypeSubst env || isEmptyVarSet (tyVarsOfType id_ty) = old_id
564 | otherwise = setIdType old_id (substTy subst id_ty)
566 id2 = zapFragileIdInfo id1
567 new_id = setVarUnique id2 (uniqFromSupply us1)
568 (us1,new_us) = splitUniqSupply us
572 %************************************************************************
574 \section{IdInfo substitution}
576 %************************************************************************
580 -> IdInfo -- Get un-substituted ones from here
581 -> IdInfo -- Substitute it and add it to here
582 -> IdInfo -- To give this
583 -- Seq'ing on the returned IdInfo is enough to cause all the
584 -- substitutions to happen completely
586 substIdInfo subst old_info new_info
589 info1 | isEmptyCoreRules old_rules = new_info
590 | otherwise = new_info `setSpecInfo` new_rules
591 -- setSpecInfo does a seq
593 new_rules = substRules subst old_rules
595 info2 | not (workerExists old_wrkr) = info1
596 | otherwise = info1 `setWorkerInfo` new_wrkr
597 -- setWorkerInfo does a seq
599 new_wrkr = substWorker subst old_wrkr
601 old_rules = specInfo old_info
602 old_wrkr = workerInfo old_info
604 substWorker :: Subst -> WorkerInfo -> WorkerInfo
605 -- Seq'ing on the returned WorkerInfo is enough to cause all the
606 -- substitutions to happen completely
608 substWorker subst NoWorker
610 substWorker subst (HasWorker w a)
611 = case lookupIdSubst subst w of
612 (DoneId w1 _) -> HasWorker w1 a
613 (DoneEx (Var w1)) -> HasWorker w1 a
614 (DoneEx other) -> WARN( True, text "substWorker: DoneEx" <+> ppr w )
615 NoWorker -- Worker has got substituted away altogether
616 (ContEx se1 e) -> WARN( True, text "substWorker: ContEx" <+> ppr w <+> ppr e)
619 substRules :: Subst -> CoreRules -> CoreRules
620 -- Seq'ing on the returned CoreRules is enough to cause all the
621 -- substitutions to happen completely
623 substRules subst rules
624 | isEmptySubst subst = rules
626 substRules subst (Rules rules rhs_fvs)
627 = seqRules new_rules `seq` new_rules
629 new_rules = Rules (map do_subst rules) (substVarSet subst rhs_fvs)
631 do_subst rule@(BuiltinRule _) = rule
632 do_subst (Rule name tpl_vars lhs_args rhs)
633 = Rule name tpl_vars'
634 (map (substExpr subst') lhs_args)
635 (substExpr subst' rhs)
637 (subst', tpl_vars') = substBndrs subst tpl_vars
639 substVarSet subst fvs
640 = foldVarSet (unionVarSet . subst_fv subst) emptyVarSet fvs
642 subst_fv subst fv = case lookupIdSubst subst fv of
643 DoneId fv' _ -> unitVarSet fv'
644 DoneEx expr -> exprFreeVars expr
645 DoneTy ty -> tyVarsOfType ty
646 ContEx se' expr -> substVarSet (setSubstEnv subst se') (exprFreeVars expr)