files for imported data types.
\begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
module TcTyDecls(
- calcRecFlags,
- calcClassCycles, calcSynCycles
+ calcRecFlags,
+ calcClassCycles, calcSynCycles
) where
#include "HsVersions.h"
import Digraph
import BasicTypes
import SrcLoc
-import Outputable
+import Maybes( mapCatMaybes )
+import Util ( isSingleton )
+import Data.List
\end{code}
%************************************************************************
-%* *
- Cycles in class and type synonym declarations
-%* *
+%* *
+ Cycles in class and type synonym declarations
+%* *
%************************************************************************
Checking for class-decl loops is easy, because we don't allow class decls
in interface files.
-We allow type synonyms in hi-boot files, but we *trust* hi-boot files,
+We allow type synonyms in hi-boot files, but we *trust* hi-boot files,
so we don't check for loops that involve them. So we only look for synonym
loops in the module being compiled.
We check for type synonym and class cycles on the *source* code.
-Main reasons:
+Main reasons:
a) Otherwise we'd need a special function to extract type-synonym tycons
- from a type, whereas we have extractHsTyNames already
+ from a type, whereas we have extractHsTyNames already
b) If we checked for type synonym loops after building the TyCon, we
- can't do a hoistForAllTys on the type synonym rhs, (else we fall into
- a black hole) which seems unclean. Apart from anything else, it'd mean
- that a type-synonym rhs could have for-alls to the right of an arrow,
- which means adding new cases to the validity checker
+ can't do a hoistForAllTys on the type synonym rhs, (else we fall into
+ a black hole) which seems unclean. Apart from anything else, it'd mean
+ that a type-synonym rhs could have for-alls to the right of an arrow,
+ which means adding new cases to the validity checker
- Indeed, in general, checking for cycles beforehand means we need to
- be less careful about black holes through synonym cycles.
+ Indeed, in general, checking for cycles beforehand means we need to
+ be less careful about black holes through synonym cycles.
-The main disadvantage is that a cycle that goes via a type synonym in an
+The main disadvantage is that a cycle that goes via a type synonym in an
.hi-boot file can lead the compiler into a loop, because it assumes that cycles
-only occur entirely within the source code of the module being compiled.
-But hi-boot files are trusted anyway, so this isn't much worse than (say)
+only occur entirely within the source code of the module being compiled.
+But hi-boot files are trusted anyway, so this isn't much worse than (say)
a kind error.
[ NOTE ----------------------------------------------
If we reverse this decision, this comment came from tcTyDecl1, and should
go back there
- -- dsHsType, not tcHsKindedType, to avoid a loop. tcHsKindedType does hoisting,
- -- which requires looking through synonyms... and therefore goes into a loop
- -- on (erroneously) recursive synonyms.
- -- Solution: do not hoist synonyms, because they'll be hoisted soon enough
- -- when they are substituted
+ -- dsHsType, not tcHsKindedType, to avoid a loop. tcHsKindedType does hoisting,
+ -- which requires looking through synonyms... and therefore goes into a loop
+ -- on (erroneously) recursive synonyms.
+ -- Solution: do not hoist synonyms, because they'll be hoisted soon enough
+ -- when they are substituted
We'd also need to add back in this definition
= nameEnvElts (go ty)
where
go :: Type -> NameEnv TyCon -- The NameEnv does duplicate elim
- go (TyVarTy v) = emptyNameEnv
- go (TyConApp tc tys) = go_tc tc tys
- go (AppTy a b) = go a `plusNameEnv` go b
- go (FunTy a b) = go a `plusNameEnv` go b
- go (PredTy (IParam _ ty)) = go ty
- go (PredTy (ClassP cls tys)) = go_s tys -- Ignore class
- go (ForAllTy _ ty) = go ty
+ go (TyVarTy v) = emptyNameEnv
+ go (TyConApp tc tys) = go_tc tc tys
+ go (AppTy a b) = go a `plusNameEnv` go b
+ go (FunTy a b) = go a `plusNameEnv` go b
+ go (PredTy (IParam _ ty)) = go ty
+ go (PredTy (ClassP cls tys)) = go_s tys -- Ignore class
+ go (ForAllTy _ ty) = go ty
go_tc tc tys | isSynTyCon tc = extendNameEnv (go_s tys) (tyConName tc) tc
- | otherwise = go_s tys
+ | otherwise = go_s tys
go_s tys = foldr (plusNameEnv . go) emptyNameEnv tys
---------------------------------------- END NOTE ]
\begin{code}
calcSynCycles :: [LTyClDecl Name] -> [SCC (LTyClDecl Name)]
calcSynCycles decls
- = stronglyConnComp syn_edges
+ = stronglyConnCompFromEdgedVertices syn_edges
where
- syn_edges = [ (ldecl, unLoc (tcdLName decl),
- mk_syn_edges (tcdSynRhs decl))
- | ldecl@(L _ decl) <- decls ]
+ syn_edges = [ (ldecl, unLoc (tcdLName decl),
+ mk_syn_edges (tcdSynRhs decl))
+ | ldecl@(L _ decl) <- decls ]
- mk_syn_edges rhs = [ tc | tc <- nameSetToList (extractHsTyNames rhs),
- not (isTyVarName tc) ]
+ mk_syn_edges rhs = [ tc | tc <- nameSetToList (extractHsTyNames rhs),
+ not (isTyVarName tc) ]
calcClassCycles :: [LTyClDecl Name] -> [[LTyClDecl Name]]
calcClassCycles decls
- = [decls | CyclicSCC decls <- stronglyConnComp cls_edges]
+ = [decls | CyclicSCC decls <- stronglyConnCompFromEdgedVertices cls_edges]
where
- cls_edges = [ (ldecl, unLoc (tcdLName decl),
- mk_cls_edges (unLoc (tcdCtxt decl)))
- | ldecl@(L _ decl) <- decls, isClassDecl decl ]
+ cls_edges = [ (ldecl, unLoc (tcdLName decl),
+ mk_cls_edges (unLoc (tcdCtxt decl)))
+ | ldecl@(L _ decl) <- decls, isClassDecl decl ]
mk_cls_edges ctxt = [ cls | L _ (HsClassP cls _) <- ctxt ]
\end{code}
%************************************************************************
-%* *
- Deciding which type constructors are recursive
-%* *
+%* *
+ Deciding which type constructors are recursive
+%* *
%************************************************************************
+Identification of recursive TyCons
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The knot-tying parameters: @rec_details_list@ is an alist mapping @Name@s to
+@TyThing@s.
+
+Identifying a TyCon as recursive serves two purposes
+
+1. Avoid infinite types. Non-recursive newtypes are treated as
+"transparent", like type synonyms, after the type checker. If we did
+this for all newtypes, we'd get infinite types. So we figure out for
+each newtype whether it is "recursive", and add a coercion if so. In
+effect, we are trying to "cut the loops" by identifying a loop-breaker.
+
+2. Avoid infinite unboxing. This is nothing to do with newtypes.
+Suppose we have
+ data T = MkT Int T
+ f (MkT x t) = f t
+Well, this function diverges, but we don't want the strictness analyser
+to diverge. But the strictness analyser will diverge because it looks
+deeper and deeper into the structure of T. (I believe there are
+examples where the function does something sane, and the strictness
+analyser still diverges, but I can't see one now.)
+
+Now, concerning (1), the FC2 branch currently adds a coercion for ALL
+newtypes. I did this as an experiment, to try to expose cases in which
+the coercions got in the way of optimisations. If it turns out that we
+can indeed always use a coercion, then we don't risk recursive types,
+and don't need to figure out what the loop breakers are.
+
+For newtype *families* though, we will always have a coercion, so they
+are always loop breakers! So you can easily adjust the current
+algorithm by simply treating all newtype families as loop breakers (and
+indeed type families). I think.
+
+
+
For newtypes, we label some as "recursive" such that
INVARIANT: there is no cycle of non-recursive newtypes
provided the invariant is maintained.
A newtype M.T is defined to be "recursive" iff
- (a) it is declared in an hi-boot file (see RdrHsSyn.hsIfaceDecl)
- (b) it is declared in a source file, but that source file has a
- companion hi-boot file which declares the type
- or (c) one can get from T's rhs to T via type
- synonyms, or non-recursive newtypes *in M*
- e.g. newtype T = MkT (T -> Int)
-
-(a) is conservative; declarations in hi-boot files are always
- made loop breakers. That's why in (b) we can restrict attention
- to tycons in M, because any loops through newtypes outside M
- will be broken by those newtypes
+ (a) it is declared in an hi-boot file (see RdrHsSyn.hsIfaceDecl)
+ (b) it is declared in a source file, but that source file has a
+ companion hi-boot file which declares the type
+ or (c) one can get from T's rhs to T via type
+ synonyms, or non-recursive newtypes *in M*
+ e.g. newtype T = MkT (T -> Int)
+
+(a) is conservative; declarations in hi-boot files are always
+ made loop breakers. That's why in (b) we can restrict attention
+ to tycons in M, because any loops through newtypes outside M
+ will be broken by those newtypes
(b) ensures that a newtype is not treated as a loop breaker in one place
and later as a non-loop-breaker. This matters in GHCi particularly, when
a newtype T might be embedded in many types in the environment, and then
The "recursive" flag for algebraic data types is irrelevant (never consulted)
for types with more than one constructor.
+
An algebraic data type M.T is "recursive" iff
- it has just one constructor, and
- (a) it is declared in an hi-boot file (see RdrHsSyn.hsIfaceDecl)
- (b) it is declared in a source file, but that source file has a
- companion hi-boot file which declares the type
- or (c) one can get from its arg types to T via type synonyms,
- or by non-recursive newtypes or non-recursive product types in M
- e.g. data T = MkT (T -> Int) Bool
+ it has just one constructor, and
+ (a) it is declared in an hi-boot file (see RdrHsSyn.hsIfaceDecl)
+ (b) it is declared in a source file, but that source file has a
+ companion hi-boot file which declares the type
+ or (c) one can get from its arg types to T via type synonyms,
+ or by non-recursive newtypes or non-recursive product types in M
+ e.g. data T = MkT (T -> Int) Bool
Just like newtype in fact
A type synonym is recursive if one can get from its
and will respond True to isHiBootTyCon. The idea is that we treat these as if one
could get from these types to anywhere. So when we see
- module Baz where
- import {-# SOURCE #-} Foo( T )
- newtype S = MkS T
+ module Baz where
+ import {-# SOURCE #-} Foo( T )
+ newtype S = MkS T
then we mark S as recursive, just in case. What that means is that if we see
- import Baz( S )
- newtype R = MkR S
+ import Baz( S )
+ newtype R = MkR S
then we don't need to look inside S to compute R's recursiveness. Since S is imported
(not from an hi-boot file), one cannot get from R back to S except via an hi-boot file,
and that means that some data type will be marked recursive along the way. So R is
unconditionly non-recursive (i.e. there'll be a loop breaker elsewhere if necessary)
-This in turn means that we grovel through fewer interface files when computing
+This in turn means that we grovel through fewer interface files when computing
recursiveness, because we need only look at the type decls in the module being
compiled, plus the outer structure of directly-mentioned types.
= is_rec
where
is_rec n | n `elemNameSet` rec_names = Recursive
- | otherwise = NonRecursive
+ | otherwise = NonRecursive
boot_name_set = availsToNameSet (md_exports boot_details)
- rec_names = boot_name_set `unionNameSets`
- nt_loop_breakers `unionNameSets`
- prod_loop_breakers
-
- all_tycons = [ tc | tycls <- tyclss,
- -- Recursion of newtypes/data types can happen via
- -- the class TyCon, so tyclss includes the class tycons
- let tc = getTyCon tycls,
- not (tyConName tc `elemNameSet` boot_name_set) ]
- -- Remove the boot_name_set because they are going
- -- to be loop breakers regardless.
-
- -------------------------------------------------
- -- NOTE
- -- These edge-construction loops rely on
- -- every loop going via tyclss, the types and classes
- -- in the module being compiled. Stuff in interface
- -- files should be correctly marked. If not (e.g. a
- -- type synonym in a hi-boot file) we can get an infinite
- -- loop. We could program round this, but it'd make the code
- -- rather less nice, so I'm not going to do that yet.
-
- --------------- Newtypes ----------------------
- new_tycons = filter isNewTyConAndNotOpen all_tycons
- isNewTyConAndNotOpen tycon = isNewTyCon tycon && not (isOpenTyCon tycon)
+ rec_names = boot_name_set `unionNameSets`
+ nt_loop_breakers `unionNameSets`
+ prod_loop_breakers
+
+ all_tycons = [ tc | tc <- mapCatMaybes getTyCon tyclss
+ -- Recursion of newtypes/data types can happen via
+ -- the class TyCon, so tyclss includes the class tycons
+ , not (tyConName tc `elemNameSet` boot_name_set) ]
+ -- Remove the boot_name_set because they are going
+ -- to be loop breakers regardless.
+
+ -------------------------------------------------
+ -- NOTE
+ -- These edge-construction loops rely on
+ -- every loop going via tyclss, the types and classes
+ -- in the module being compiled. Stuff in interface
+ -- files should be correctly marked. If not (e.g. a
+ -- type synonym in a hi-boot file) we can get an infinite
+ -- loop. We could program round this, but it'd make the code
+ -- rather less nice, so I'm not going to do that yet.
+
+ single_con_tycons = filter (isSingleton . tyConDataCons) all_tycons
+ -- Both newtypes and data types, with exactly one data constructor
+ (new_tycons, prod_tycons) = partition isNewTyCon single_con_tycons
+ -- NB: we do *not* call isProductTyCon because that checks
+ -- for vanilla-ness of data constructors; and that depends
+ -- on empty existential type variables; and that is figured
+ -- out by tcResultType; which uses tcMatchTy; which uses
+ -- coreView; which calls coreExpandTyCon_maybe; which uses
+ -- the recursiveness of the TyCon. Result... a black hole.
+ -- YUK YUK YUK
+
+ --------------- Newtypes ----------------------
nt_loop_breakers = mkNameSet (findLoopBreakers nt_edges)
is_rec_nt tc = tyConName tc `elemNameSet` nt_loop_breakers
- -- is_rec_nt is a locally-used helper function
+ -- is_rec_nt is a locally-used helper function
nt_edges = [(t, mk_nt_edges t) | t <- new_tycons]
- mk_nt_edges nt -- Invariant: nt is a newtype
- = concatMap (mk_nt_edges1 nt) (tcTyConsOfType (new_tc_rhs nt))
- -- tyConsOfType looks through synonyms
+ mk_nt_edges nt -- Invariant: nt is a newtype
+ = concatMap (mk_nt_edges1 nt) (tcTyConsOfType (new_tc_rhs nt))
+ -- tyConsOfType looks through synonyms
- mk_nt_edges1 nt tc
- | tc `elem` new_tycons = [tc] -- Loop
- -- At this point we know that either it's a local *data* type,
- -- or it's imported. Either way, it can't form part of a newtype cycle
- | otherwise = []
+ mk_nt_edges1 _ tc
+ | tc `elem` new_tycons = [tc] -- Loop
+ -- At this point we know that either it's a local *data* type,
+ -- or it's imported. Either way, it can't form part of a newtype cycle
+ | otherwise = []
- --------------- Product types ----------------------
- -- The "prod_tycons" are the non-newtype products
- prod_tycons = [tc | tc <- all_tycons,
- not (isNewTyCon tc), isProductTyCon tc]
+ --------------- Product types ----------------------
prod_loop_breakers = mkNameSet (findLoopBreakers prod_edges)
prod_edges = [(tc, mk_prod_edges tc) | tc <- prod_tycons]
-
- mk_prod_edges tc -- Invariant: tc is a product tycon
- = concatMap (mk_prod_edges1 tc) (dataConOrigArgTys (head (tyConDataCons tc)))
+
+ mk_prod_edges tc -- Invariant: tc is a product tycon
+ = concatMap (mk_prod_edges1 tc) (dataConOrigArgTys (head (tyConDataCons tc)))
mk_prod_edges1 ptc ty = concatMap (mk_prod_edges2 ptc) (tcTyConsOfType ty)
- mk_prod_edges2 ptc tc
- | tc `elem` prod_tycons = [tc] -- Local product
- | tc `elem` new_tycons = if is_rec_nt tc -- Local newtype
- then []
- else mk_prod_edges1 ptc (new_tc_rhs tc)
- -- At this point we know that either it's a local non-product data type,
- -- or it's imported. Either way, it can't form part of a cycle
- | otherwise = []
-
-new_tc_rhs tc = snd (newTyConRhs tc) -- Ignore the type variables
-
-getTyCon (ATyCon tc) = tc
-getTyCon (AClass cl) = classTyCon cl
-getTyCon other = panic "getTyCon"
+ mk_prod_edges2 ptc tc
+ | tc `elem` prod_tycons = [tc] -- Local product
+ | tc `elem` new_tycons = if is_rec_nt tc -- Local newtype
+ then []
+ else mk_prod_edges1 ptc (new_tc_rhs tc)
+ -- At this point we know that either it's a local non-product data type,
+ -- or it's imported. Either way, it can't form part of a cycle
+ | otherwise = []
+
+new_tc_rhs :: TyCon -> Type
+new_tc_rhs tc = snd (newTyConRhs tc) -- Ignore the type variables
+
+getTyCon :: TyThing -> Maybe TyCon
+getTyCon (ATyCon tc) = Just tc
+getTyCon (AClass cl) = Just (classTyCon cl)
+getTyCon _ = Nothing
findLoopBreakers :: [(TyCon, [TyCon])] -> [Name]
-- Finds a set of tycons that cut all loops
= go [(tc,tc,ds) | (tc,ds) <- deps]
where
go edges = [ name
- | CyclicSCC ((tc,_,_) : edges') <- stronglyConnCompR edges,
- name <- tyConName tc : go edges']
+ | CyclicSCC ((tc,_,_) : edges') <- stronglyConnCompFromEdgedVerticesR edges,
+ name <- tyConName tc : go edges']
\end{code}
These two functions know about type representations, so they could be
-in Type or TcType -- but they are very specialised to this module, so
+in Type or TcType -- but they are very specialised to this module, so
I've chosen to put them here.
\begin{code}
tcTyConsOfType :: Type -> [TyCon]
--- tcTyConsOfType looks through all synonyms, but not through any newtypes.
+-- tcTyConsOfType looks through all synonyms, but not through any newtypes.
-- When it finds a Class, it returns the class TyCon. The reaons it's here
-- (not in Type.lhs) is because it is newtype-aware.
-tcTyConsOfType ty
+tcTyConsOfType ty
= nameEnvElts (go ty)
where
go :: Type -> NameEnv TyCon -- The NameEnv does duplicate elim
go ty | Just ty' <- tcView ty = go ty'
- go (TyVarTy v) = emptyNameEnv
- go (TyConApp tc tys) = go_tc tc tys
- go (AppTy a b) = go a `plusNameEnv` go b
- go (FunTy a b) = go a `plusNameEnv` go b
+ go (TyVarTy _) = emptyNameEnv
+ go (TyConApp tc tys) = go_tc tc tys
+ go (AppTy a b) = go a `plusNameEnv` go b
+ go (FunTy a b) = go a `plusNameEnv` go b
go (PredTy (IParam _ ty)) = go ty
go (PredTy (ClassP cls tys)) = go_tc (classTyCon cls) tys
- go (ForAllTy _ ty) = go ty
- go other = panic "tcTyConsOfType"
+ go (PredTy (EqPred ty1 ty2)) = go ty1 `plusNameEnv` go ty2
+ go (ForAllTy _ ty) = go ty
go_tc tc tys = extendNameEnv (go_s tys) (tyConName tc) tc
go_s tys = foldr (plusNameEnv . go) emptyNameEnv tys
projects / ghc-hetmet.git / blobdiff