HaRe-0.6: tools/base/SA/Scope.hs
-- $Id: Scope.hs,v 1.18 2001/08/21 00:13:36 hallgren Exp $
-- This module implements the static checker, and is way too big and really
-- must be split up some day.
module Scope(Senv(..),
patBound,
names,
allNames,
allTypNames,
instPatToParts,
typePatToParts,
boundInP,
fst3,
fst4,
env0,
freeT,
freeC,
freeD,
restrictTvar,
runScope)
where
import Syntax
import List(find, nub, nubBy, (\\), sortBy, groupBy, union)
--import Observe
import PrettyPrint
import Maybe
import IOExts
import SyntaxUtil(isTyVar, getTyName)
import Scope2
import GenSym(newName)
------------------------------------------------------------------
-- Environments
------------------------------------------------------------------
-- What kind of names are introduced by a declaration?
-- Classes, Types, Data Constructors, Variables, Signatures, and Modules
-- So we define an abstract class for environments, which has an empty
-- environment, env0, and extension functions for each kind of name.
type Arity = Int
data KindOfName = Var | Cons | TyVar | TyCons | Class | Mod | Sig
data KindOfTyCons = DataDef | NewTypeDef | TypeDef
class Env env where
extClass :: HsName -> SrcLoc -> Arity -> [HsName] -> env -> env
extTconstr :: HsName -> SrcLoc -> Arity -> Bool -> env -> env
extTvar :: HsName -> env -> env
extConstr :: HsName -> SrcLoc -> Arity -> env -> env
extVar :: HsName -> SrcLoc -> env -> env
extSig :: HsName -> SrcLoc -> env -> env
extMod :: HsName -> env -> env
env0 :: env
restrictTvar :: env -> env
-------------------------------------------------------------------------------
-- A concrete class for environments appropriate for static Checking
type Error = (SrcLoc,String)
locations :: KindOfName -> Senv -> [(HsName,SrcLoc)]
locations k env =
case k of
Var -> varNames env
Sig -> sigNames env
Cons -> map (\(nm,loc,arity) -> (nm,loc)) $ constrNames env
Class -> map (\(nm,loc,arity,nms) -> (nm,loc)) $ classNames env
TyCons-> map (\(nm,loc,arity,issyn) -> (nm,loc)) $ tconstrNames env
other -> error "no locations available "
data Senv = S { classNames :: [(HsName,SrcLoc,Arity,[HsName])]
, tconstrNames :: [(HsName,SrcLoc,Arity,Bool)]
, tvarNames :: [HsName]
, constrNames :: [(HsName,SrcLoc,Arity)]
, varNames :: [(HsName,SrcLoc)]
, sigNames :: [(HsName,SrcLoc)]
, moduleNames :: [HsName]
} deriving Show
instance Env Senv where
extClass nm l a nms env = env {classNames = (nm,l,a,nms): classNames env}
extTconstr nm l a syn env = env {tconstrNames = (nm,l,a,syn): tconstrNames env}
extTvar nm env = env {tvarNames = (nm) : tvarNames env}
extConstr nm l a env = env {constrNames = (nm,l,a) : constrNames env}
extVar nm l env = env {varNames = (nm,l) : varNames env}
extSig nm l env = env {sigNames = (nm,l) : sigNames env}
extMod nm env = env {moduleNames = nm : moduleNames env}
env0 = let e = (S [] [] [] [] [] [] [])
in e
restrictTvar env = env {tvarNames = []}
concatEnv :: Senv -> Senv -> Senv
concatEnv (S a b c d e f g) (S a' b' c' d' e' f' g') =
S (a++a') (b++b') (c++c') (d++d') (e++e') (f++f') (g ++ g')
fst3 (a,b,c) = a
snd3 (a,b,c) = b
thd3 (a,b,c) = c
fst4 (a,b,c,d) = a
snd4 (a,b,c,d) = b
thd4 (a,b,c,d) = c
fth4 (a,b,c,d) = d
varDefined s env = any (==s) $ map fst $ varNames env
classDefined s env = any (==s) $ map fst4 $ classNames env
tvarDefined s env = any (==s) $ tvarNames env
tconDefined s env = (any (==s) $ map fst4 $ tconstrNames env)
|| (any (==s) [Qual (Module "Prelude") "()", Qual (Module "Prelude") "[]"])
sigExists s env = any (==s) $ map fst $ sigNames env
isMethod nm c env = case classMethods c env of
Just nms -> nm `elem` nms
Nothing -> False
classMethods :: HsName -> Senv -> Maybe [HsName]
classMethods nm env = fmap fth4 (List.find match (classNames env))
where match (name,_,_,nms) = name==nm
match _ = False
synArity :: HsName -> Senv -> Maybe Int
synArity nm env = fmap thd4 (List.find match (tconstrNames env))
where match (name,_,_,True) = name==nm
match _ = False
cArity :: HsName -> Senv -> Maybe Int
cArity (UnQual ":") _ = Just 2
cArity (Qual (Module "Prelude") ":") _ = Just 2
cArity (UnQual "()") _ = Just 0
cArity (Qual (Module "Prelude") "()" ) _ = Just 0
cArity c env = fmap thd3 (List.find match (constrNames env))
where match (name,_,_) = name == c
-- expects C x*
typePatToParts t = extractConArgs t []
where extractConArgs (Typ (HsTyCon c)) acc = (c, acc)
extractConArgs (Typ (HsTyApp f (Typ (HsTyVar x)))) acc =
extractConArgs f (x:acc)
extractConArgs t acc =
(UnQual newName, acc)
--expects C t*
instPatToParts t = extractInstArgs t []
where extractInstArgs (Typ (HsTyApp (Typ(HsTyCon c)) x)) acc = (c, acc)
extractInstArgs (Typ (HsTyApp f x)) acc =
extractInstArgs f (x:acc)
extractInstArgs _ acc =
error ("ill formed instance pattern:\n\n" ++ pp t)
------------------------------------------------------------------
-- Given a list of mutually recursive declarations, what names are
-- introduced in the scope of those declarations?
names :: HsDecl -> Senv
names (Dec d) =
case d of
HsTypeDecl s (nm:args) body ->
env0 { tconstrNames = [(getTyName nm, s, length args, True)] }
HsNewTypeDecl s cntxt (c:args) body der ->
env0 { tconstrNames = [(getTyName c, s, length args, False)]
, constrNames = [dataName body]
, varNames = recordName body
}
HsDataDecl s cntxt (c:args) constrs der ->
let f x xs = (dataName x) : xs
g x xs = (recordName x) ++ xs
in env0 { tconstrNames = [(getTyName c, s, length args, False)]
, constrNames = foldr f [] constrs
, varNames = foldr g [] constrs
}
HsClassDecl s c tp ds ->
let (con, args) = typePatToParts tp
members = sigNames $ allNames ds env0
in env0 { varNames = members
, classNames = [(con, s, length args, map fst members)]
}
HsInstDecl s c tp ds -> env0
HsDefaultDecl s t -> env0
HsTypeSig s nms c t -> env0 {sigNames = map (\nm -> (nm,s)) nms}
HsFunBind s ((HsMatch s2 nm ps rhs ds):_) -> env0 {varNames = [(nm,s2)]}
HsPatBind s p rhs ds -> env0 {varNames = map (\nm -> (nm,s)) $ boundInP p []}
HsPrimitiveTypeDecl s c nm ->
env0 { tconstrNames = [(nm,s,0,False)] }
HsPrimitiveBind s nm typ ->
env0 { varNames = [(nm,s)] }
other -> env0
dataName (HsConDecl s nm slots) = (nm,s,length slots)
dataName (HsRecDecl s nm slots) = (nm,s,length slots)
recordName :: HsConDecl t -> [(HsName,SrcLoc)]
recordName (HsConDecl s nm slots) = []
recordName (HsRecDecl s nm slots) = foldr f [] slots
where f (names,domain) xs = map (\nm -> (nm,s)) names ++ xs
allNames :: [HsDecl] -> Senv -> Senv
allNames ds initial = foldr acc initial ds
where acc d env = concatEnv (names d) env
----------------------------------------------------------------------
-- Generic Static checking functions
duplicates :: Eq a => [a] -> [a]
duplicates [] = []
duplicates (x:xs) =
if elem x xs then x : (duplicates (filter (/=x) xs)) else (duplicates xs)
collect_duplicate_info :: ([a] -> [b]) -> (a -> a -> Ordering) -> [a] -> [b]
collect_duplicate_info infof compare =
concat . (map infof) . (groupBy (lift compare)) . (List.sortBy compare)
where lift g x y = case g x y of { EQ -> True; _ -> False }
dupErrs :: (Show a, Show b) => b -> [(a,SrcLoc)] -> [Error]
dupErrs sort [] = []
dupErrs sort [x] =[]
dupErrs sort xs@((nm,loc):_) = chk loc True (duplicate_things sort nm (map snd xs))
dupTvErr srcloc [x] = []
dupTvErr srcloc (x:xs) = [(srcloc, duplicate_type_vars x)]
chk:: SrcLoc -> Bool -> String -> [Error]
chk loc test message = if test then [(loc,message)] else []
unique :: Eq a => [(a,b)] -> [(a,b)]
unique = nubBy (\(a,_) (b,_) -> a==b)
------------------------------------------------------------------------------
-- Scope checking
------------------------------------------------------------------------------
nmConflict :: Senv -> [Error]
nmConflict env =
let ts = tconstrNames env
cs = classNames env
sameName (tn,tloc,_,_) errs =
case List.find (\(a,_,_,_) -> a==tn) cs of
Nothing -> errs
Just (_,cloc,_,_) -> (tloc, type_class_conflict tn [tloc,cloc]) : errs
in foldr sameName [] ts
classMethodErr :: Senv -> [Error]
classMethodErr env =
let ss = sigNames env
vs = varNames env
sigExists (vn,vloc) errs =
case List.find (\(a,_) -> a==vn) ss of
Nothing -> (vloc, method_without_signature vn) : errs
Just _ -> errs
in foldr sigExists [] vs
type_class_conflict tn cloc =
"Type name " ++ pp tn ++ " is used as class name "++ pp cloc
method_without_signature vn =
"Definition of " ++ pp vn ++ " without declaration"
getClass (Typ (HsTyApp x _)) = getClass x
getClass (Typ (HsTyCon c)) = Just c
getClass _ = Nothing
allTypNames (Typ (HsTyVar v)) (vs, cs) = (v : vs, cs)
allTypNames (Typ (HsTyCon c)) (vs, cs) = (vs, c : cs)
allTypNames (Typ t) ans = accT allTypNames t ans
isTyConApp (Typ (HsTyCon _)) = True
isTyConApp (Typ (HsTyApp f _)) = isTyConApp f
isTyConApp _ = False
getTyAppArgs (Typ (HsTyCon _)) args = args
getTyAppArgs (Typ (HsTyApp f x)) args = getTyAppArgs f (x:args)
-- Well formed type expression: C x*
wfTp :: SrcLoc -> TPContext -> HsType -> [Error] -> [Error]
wfTp srcloc c t errs =
if isTyConApp t && all isTyVar (getTyAppArgs t []) then
errs
else
(srcloc, type_former_is_not_constructor t c) : errs
-- well formed simple class specification: C x+
wfSclass :: SrcLoc -> HsType -> [Error] -> [Error]
wfSclass loc t errs =
if isTyConApp t && not (null args) && all isTyVar args then
errs
else
(loc, illformed_sclass t) : errs
where args = getTyAppArgs t []
-------------------------------------------------------------------------
srcloc (HsTypeDecl loc _ _ ) = loc
srcloc (HsNewTypeDecl loc _ _ _ _ ) = loc
srcloc (HsDataDecl loc _ _ _ _ ) = loc
srcloc (HsClassDecl loc _ _ _ ) = loc
srcloc (HsInstDecl loc _ _ _ ) = loc
srcloc (HsDefaultDecl loc _ ) = loc
srcloc (HsTypeSig loc _ _ _ ) = loc
srcloc (HsFunBind loc _ ) = loc
srcloc (HsPatBind loc _ _ _ ) = loc
srcloc (HsPrimitiveTypeDecl loc _ _ ) = loc
srcloc (HsPrimitiveBind loc _ _ ) = loc
whatIs (HsTypeDecl _ _ _ ) = "type declaration"
whatIs (HsNewTypeDecl _ _ _ _ _ ) = "newtype declaration"
whatIs (HsDataDecl _ _ _ _ _ ) = "data declaration"
whatIs (HsClassDecl _ _ _ _ ) = "class declaration"
whatIs (HsInstDecl _ _ _ _ ) = "instance declaration"
whatIs (HsDefaultDecl _ _ ) = "declaration"
whatIs (HsTypeSig _ _ _ _ ) = "type signature"
whatIs (HsFunBind _ _ ) = "function binding"
whatIs (HsPatBind _ _ _ _ ) = "pattern binding"
whatIs (HsPrimitiveTypeDecl _ _ _ ) = "declaration"
whatIs (HsPrimitiveBind _ _ _ ) = "declaration"
--------------------------------------------------------------
-- The first kind of scoping and its combinators
--------------------------------------------------------------
scopE :: v -> E (v -> e) (v->v,v -> p) (v->v,v -> ds) (v -> t) (v -> c) -> E e p ds t c
scopE env x =
case x of
HsLet (envtrans,f) e -> let env2 = envtrans env
in HsLet (f env2) (e env2)
HsLambda ps e -> let (env2,ps') = scopPatList env ps
in HsLambda ps' (e env2)
HsCase e alts -> HsCase (e env) (map (scopAlt env) alts)
HsDo stmt -> HsDo (scopStmt env stmt)
HsListComp stmt -> HsListComp (scopStmt env stmt)
z -> mapE (\ f -> f env) (error "missing HsExp case")
(error "missing HsDecl case") (\ f -> f env) (\ f -> f env) z
scopAlt :: v -> HsAlt (v -> e) (v->v,v -> p) (v->v,v -> ds) -> HsAlt e p ds
scopAlt env (HsAlt s (f,pf) rhs (g,dsf)) =
let env2 = g (f env)
in (HsAlt s (pf env) (scopRhs env2 rhs) (dsf env2))
scopRhs :: v -> HsRhs (v -> e) -> HsRhs e
scopRhs env x = mapRhs (\ f -> f env) x
scopStmt :: v -> HsStmt (v -> e) (v->v,v -> p) (v->v,v -> ds) -> HsStmt e p ds
scopStmt env (HsGenerator (tr,pf) e s) =
let env2 = tr env in HsGenerator (pf env) (e env2) (scopStmt env2 s)
scopStmt env (HsQualifier e s) = HsQualifier (e env) (scopStmt env s)
scopStmt env (HsLetStmt (tf,dsf) s) =
let env2 = tf env in HsLetStmt (dsf env2) (scopStmt env2 s)
scopStmt env (HsLast e) = HsLast (e env)
scopPatList :: v -> [(v -> v,v -> p)] -> (v,[p])
scopPatList env ps = (foldr (\ (tf,_ ) e -> tf e) env ps,
map (\ (_ ,pf) -> pf env) ps)
--------------------------------------------------------------------------
-- Then for the declaration sub-language
scopD :: Env v => v ->
D (v -> e)
(v -> v, v -> p)
(v -> v, v -> ds)
(v -> t)
(v -> c)
(v -> v, v -> tp) ->
D e p ds t c tp
scopD env x =
let scopConDecl env = mapConDecl (\f -> f env)
extendWithTvs env tvs = foldr extTvar env tvs
scopMatch env (HsMatch loc nm ps rhs (dectrans,ds)) =
let (env2,ps') = scopPatList env ps
env3 = dectrans (extVar nm loc env2)
in HsMatch loc nm ps' (scopRhs env3 rhs) (ds env3)
in
case x of
HsPatBind loc (pattrans,pf) rhs (dectrans,dsf) ->
let env2 = dectrans (pattrans env)
in
HsPatBind loc (pf env) (scopRhs env2 rhs) (dsf env2)
HsFunBind loc matches -> HsFunBind loc (map (scopMatch env) matches)
HsTypeDecl loc (transtpfs @ ((ctrans,cmaker):fs)) tf ->
let env2 = ctrans env
constr = cmaker env
(env3,args) = scopPatList env fs
in HsTypeDecl loc (constr:args) (tf env3)
HsNewTypeDecl loc contxtf transtpfs condecl derivs ->
let (env2,args) = scopPatList env transtpfs
(env3,_) = scopPatList (restrictTvar env) (tail transtpfs)
in HsNewTypeDecl loc (contxtf env3) args (scopConDecl env2 condecl) derivs
HsDataDecl loc contxtf transtpfs condecls derivs ->
let (env2,args) = scopPatList env transtpfs
(env3,_) = scopPatList (restrictTvar env) (tail transtpfs)
in HsDataDecl loc (contxtf env3) args (map (scopConDecl env2) condecls) derivs
HsClassDecl loc contxtf (trans,tpf) (dectrans,dsf) ->
let env1 = trans (restrictTvar env)
in HsClassDecl loc (contxtf env1) (tpf env) (dsf $ dectrans env1)
HsInstDecl loc contxtf (trans,tpf) (dectrans,dsf) ->
let env1 = trans (restrictTvar env)
in HsInstDecl loc (contxtf env1) (tpf env) (dsf $ dectrans env1)
HsTypeSig loc nms contxtf (transf, tpf) ->
HsTypeSig loc nms (contxtf (transf env)) (tpf env)
z -> mapD (\ f -> f env) h h (\ f -> f env) (\ f -> f env) (error "type pattern") z
where h (trans,f) = f (trans env)
--------------------------------------------------------------------------
-- Then for the type sub-language
scopT :: v -> T (v -> t) -> T t
scopT env t = mapT (\f -> f env) t
--------------------------------------------------------------------------
-- Computing Things about patterns
--------------------------------------------------------------------------
boundInP :: HsPat -> [HsName] -> [HsName]
boundInP (Pat(HsPId(HsVar s))) ans = s:ans
boundInP (Pat(HsPAsPat n p)) ans = boundInP p (n:ans)
boundInP (Pat x) ans = accP boundInP ans x
------------------------------------------------------------------------
-- patBound: Compute three things while visiting each pattern sub-node.
-- 1) A list of unique names bound by the pattern
-- 2) A list of names that appear more than once.
-- These are errors because we allow only linear patterns
-- 3) A list of every construtor and the arity at which it was used.
-- These are potential errors if the arites do not match
patBound :: HsPat -> ([HsName], [HsName], [(HsName, Int)]) ->
([HsName], [HsName], [(HsName, Int)])
patBound (Pat p) ans =
case p of
HsPId(HsVar n) -> add n ans
HsPAsPat n p -> patBound p (add n ans)
HsPApp c ps -> cadd c (length ps) ans'
HsPInfixApp p1 c p2 -> cadd (getHSName c) 2 ans'
_ -> ans'
where add x (a, b, c) =
if elem x a
then if elem x b
then (a, b, c)
else (a, x:b, c)
else (x:a, b, c)
cadd c n (x, y, z) = (x, y, (c, n):z)
ans' = accP patBound ans p
------------------------------------------------------------------------------
-- Static Check for Expressions
chE :: SrcLoc -> HsExp -> Senv -> [Error]
chE loc (exp @ (Exp x)) env =
case scopE env (mapE (chE loc) (chP loc)
(chDs WhereLikeDecl) (chT loc ) (error "ctxt") x) of
HsId (HsVar n) -> chk loc (not (varDefined n env)) (undefined_variable n)
HsInfixApp x (HsVar n) y -> chk loc (not (varDefined n env)) (undefined_variable n)
HsLeftSection x (HsVar n) -> chk loc (not (varDefined n env)) (undefined_variable n)
HsRightSection (HsVar n) x -> chk loc (not (varDefined n env)) (undefined_variable n)
HsLambda ps e -> e ++ (chPatList loc env ps)
z -> accE (++) (\ (ns,errs) a -> errs++a) (++) (++) (++) z []
--------------------------------------------
-- Static checks for individual patterns
chP :: SrcLoc -> HsPat -> (Senv -> Senv,Senv -> ([HsName],[Error]))
chP loc (pat @ (Pat x)) = (envTrans, f)
where (uniqueNames,dups,constrArities) = patBound pat ([],[],[])
envTrans env = foldr extName env uniqueNames
extName nm = extVar nm loc
duperr = chk loc (not (null dups)) (duplicate_vars_in_pattern dups)
f env = (uniqueNames,allErrors env)
allErrors env = foldr arityCheck duperr constrArities
where arityCheck (c,n) ans = check c n (cArity c env) ++ ans
check c n Nothing = [(loc,undefined_constr c)]
check c n (Just m) = chk loc (m /=n) (constr_wrong_arity n c)
-----------------------------------------------------------------------------
-- When language constructs have a list of patterns like : (\ p1 ... pn -> e)
-- or (case x of { C p1 ... pn -> e }), Haskell has the rule that no variable
-- should appear more than once in the list. We can't check this, pattern by
-- pattern, but have to observe the complete list. If we map (chP env) over a
-- list of patterns we get [([unique_names],[error_messages])], from this we
-- can compute additional error_messages dealing with duplicates.
chPatList :: SrcLoc -> Senv -> [([HsName],[Error])] -> [Error]
chPatList loc env ps =
let accumulate (ns,errs) (names,errors) = (ns++names,errs++errors)
(allbound,internalerr) = foldr accumulate ([],[]) ps
dups = duplicates allbound
duperr = chk loc (not (null dups)) (repeated_pattern_variables dups)
in internalerr ++ duperr
--------------------------------------------------------------------------
-- static checks for a list of Decls
chDs :: DeclContext -> [HsDecl] -> (Senv->Senv,Senv -> [Error] )
chDs contxt ds = (envtrans,errorfun)
where env = allNames ds env0
envtrans = concatEnv env
errorfun env = foldr (\ d ans -> (check env d) ++ ans) allErrors ds
sameName (x,y) (a,b) = compare x a
contextErrors = catMaybes $ map (legal contxt) ds
dupErr k message = collect_duplicate_info (dupErrs message) sameName (locations k env)
dupValErrors = dupErr Var "value definitions"
dupSigErrors = dupErr Sig "type signatures"
dupClsErrors = dupErr Class "class definitions"
dupTypErrors = dupErr TyCons "type definitions"
dupConsErrors = dupErr Cons "constructor functions"
allErrors = contextErrors++dupValErrors++dupSigErrors++dupClsErrors
++ dupTypErrors ++ dupConsErrors ++ nmConflict env ++ clsMethodErr
sigerr loc name = chk loc ((not $ elem name (map fst (varNames env))) && contxt/=ClassDecl)
(signature_without_definition name)
methodErr c (nm,loc) = chk loc (not $ isMethod nm c env) (not_a_method nm c)
clsMethodErr = case contxt of
ClassDecl -> classMethodErr env
other -> []
check env (Dec x) =
let loc = srcloc x
methodErrs (HsInstDecl loc c tp ds) =
let nms = varNames $ allNames ds env0
in case getClass tp of
Nothing -> []
Just c -> concat $ map (methodErr c) nms
in
case scopD env (mapD' (chE loc) (chP loc) (chDs) (chT loc) (chCntxt loc) (chTp loc) x) of
HsTypeSig loc nms c t -> (concat $ map (sigerr loc) nms)++c++t
HsInstDecl loc c tp ds -> methodErrs x ++ c ++ tp ++ ds
z -> accD (++) (\ (ns,errs) a -> (errs)++a) (++) (++) (++) (++) z []
---------------------------------------------------------------------------
chT :: SrcLoc -> HsType -> Senv -> [Error]
chT loc (typ @ (Typ t)) env =
case t of
HsTyVar nm -> chk loc (not (tvarDefined nm env)) (undefined_tvar nm)
HsTyCon nm -> chk loc (not (tconDefined nm env)) (undefined_tcon nm)
HsTyApp (Typ f) x -> synCheck (chT loc) loc env f x 1
z -> accT (++) (scopT env (mapT (chT loc) z)) []
synCheck chf loc env (HsTyCon c) arg n =
case synArity c env of
Nothing -> chk loc (not (tconDefined c env)) (undefined_tcon c) ++
chf arg env
Just m -> chk loc (m/=n) (tysynonym_not_fully_applied c) ++ chf arg env
synCheck chf loc env (HsTyApp (Typ f) x) arg n =
synCheck chf loc env f x (n+1) ++ chf arg env
synCheck chf loc env t arg n = chf (Typ t) env ++ chf arg env
-----------------------------------------------------------------------------
-- Static checks for contexts
chCntxt :: SrcLoc -> DeclContext -> [HsType] -> (Senv -> [Error])
chCntxt loc c ts env = foldr (check c) [] ts
where inscope (Typ (HsTyVar x)) ans =
chk loc (not $ tvarDefined x env) (undefined_tvar_in_context x) ++ ans
inscope (Typ (HsTyCon c)) ans =
chk loc (not $ classDefined c env) (undefined_class_in_context c) ++ ans
inscope (Typ x) ans = accT inscope x ans
-- class: C (x t*)+
wfClass t (Typ (HsTyApp (Typ (HsTyCon c)) x )) xs =
wfClassArg x x xs
wfClass t (Typ (HsTyApp x y )) xs =
wfClass t x $ wfClassArg x x xs
wfClass t (Typ x) xs =
(loc, illformed_class t) : xs
-- class arg: x t*
wfClassArg t (Typ (HsTyVar y)) xs = xs
wfClassArg t (Typ (HsTyApp x _)) xs = wfClassArg t x xs
wfClassArg t (Typ x) xs = (loc, illformed_class_arg t) : xs
check ClassDecl x ans = wfSclass loc x (inscope x ans)
check InstDecl x ans = wfSclass loc x (inscope x ans)
check _ x ans = wfClass x x (inscope x ans)
-----------------------------------------------------------------------------
-- Static checks for type patterns
chTp :: SrcLoc -> TPContext -> HsType -> (Senv -> Senv, Senv -> [Error])
chTp srcloc InstTP x =
let errors = wf x []
-- well formed instance: C (C x*)+
wf (Typ(HsTyApp (Typ(HsTyCon c)) arg)) xs =
wfTp srcloc InstTP arg xs
wf (Typ(HsTyCon c)) xs =
(srcloc, instance_required c) : xs
wf (Typ(HsTyApp y arg)) xs =
wf y (wfTp srcloc InstTP arg xs)
wf tp xs =
(srcloc, instance_not_class_app tp) : xs
(classname, ts) = instPatToParts x
(tvs, cs) = foldr allTypNames ([], []) ts
trans env = if null errors then foldr extTvar env tvs else env
clsError env = chk srcloc (not $ classDefined classname env)
(undefined_class_in_instance classname)
cdef env c ans =
if tconDefined c env
then case synArity c env of
Nothing -> ans
Just _ -> (srcloc, synonym_illegal_in_instance c):ans
else (srcloc,undefined_tcon_in_instance c):ans
dupErrs = collect_duplicate_info (dupTvErr srcloc) compare tvs
tpf env = if null errors
then foldr (cdef env) (dupErrs ++ clsError env) cs
else errors
in (trans, tpf)
chTp srcloc SigTP x =
let (tvs, cs) = allTypNames x ([], [])
trans env = foldr extTvar env tvs
cdef env c ans =
if tconDefined c env
then ans
else (srcloc, undefined_tcon_in_signature c):ans
tpf env = foldr (cdef env) [] cs
in (trans, tpf)
chTp srcloc cntxt x =
let (constr, tvs) = typePatToParts x
errors = case cntxt of DataLikeTP -> wfTp srcloc cntxt x []
ClassTP -> wfSclass srcloc x []
trans env = if null errors then foldr extTvar env tvs else env
tpf env = if null errors
then collect_duplicate_info (dupTvErr srcloc) compare tvs
else errors
in (trans, tpf)
-------------------------------------------------------------------------
-- Error Message Strings are computed here
-------------------------------------------------------------------------
undefined_variable nm = "Undefined variable: "++ pp nm
duplicate_vars_in_pattern dups =
"Variables appear more than once in single pattern: " ++ pp dups
undefined_constr c =
"Undefined Constructor in pattern: " ++ pp c
constr_wrong_arity n c =
"Constructor "++ pp c++ " must have exactly "++ pp n ++ " arguments."
repeated_pattern_variables dups =
"Repeated variables in pattern list: " ++ pp dups
duplicate_things sort name locs =
"Duplicate " ++ show sort ++ " of " ++ show name ++
" at locations: " ++ pp locs
signature_without_definition name =
"Signature for "++pp name++" without matching definition."
undefined_class_in_instance classname =
"Class name in instance: " ++ pp classname ++ " is not defined"
undefined_tcon_in_instance c =
"Type constructor " ++ pp c ++ " in instance is not defined"
synonym_illegal_in_instance c =
"Type synonym " ++ pp c ++ " in instance"
undefined_tcon_in_signature c =
"Type constructor " ++ pp c ++ " in signature is not defined"
undefined_class_in_context clsname =
"Class name " ++ pp clsname ++ " in context is not defined"
undefined_tvar_in_context tvarname =
"Type variable " ++ pp tvarname ++ " in context is not defined"
undefined_tvar tvarname =
"Type variable " ++ pp tvarname ++ " is not defined"
undefined_tcon tconname =
"Type constructor " ++ pp tconname ++ " is not defined"
tysynonym_not_fully_applied tyconname =
"Type synonym " ++ pp tyconname ++ " is not fully applied"
duplicate_type_vars x =
"Duplicate type variables in definition: " ++ pp x
non_tyvar_arg_in_pattern a c =
"Argument in Type Pattern in " ++ show c ++ " is not a variable: "++ pp a
type_former_is_not_constructor x c =
"Type pattern in " ++ show c ++ " is not an application of a type constructor: "++ pp x
instance_required tp =
"Instance of class " ++ pp tp ++ " required"
instance_not_class_app tp =
"Instance is not an application of a class constructor: "++pp tp
illformed_sclass t=
"ill formed class "++pp t
illformed_class t=
"ill formed class in context "++pp t
illformed_class_arg t=
"ill formed argument " ++ pp t ++ " to class in context "
not_a_method nm c =
pp nm ++ " is not a method of class " ++ pp c
run env prog = errF (envF env) where (envF, errF) = chDs TopDecl prog
runScope = run env0
{-
showAst === pp
showAst :: Printable a => a -> String
showAst = render . ppi
-}
{-
testDs :: (String,[HsDecl]) -> IO ()
testDs (s, ds) =
do { putStr "\n==============================================\n"
; putStr s
; putStr "\n--- test code----------\n"
; sh ds
; putStr "\n--- errors ------------\n"
; (putStr . unlines . map showErr . run env0) ds
}
tests ts = sequence_ $ map testDs ts
-}
-----------------------------------------------------------------------------
-- computing free variables
-- Computing free variables is a tricky computation, because the same variable
-- may be free in one spot and bound in another. We need an environment to
-- determine what variables are bound at any particular point. We use a list
-- of HsName as the environment
-- Given an expression and an environment telling what vars are bound
-- determine the free variables in the expression.
freeE :: HsExp -> [HsName] -> [HsName]
freeE (Exp x) env =
case scopE env (mapE freeE freeP freeD freeT freeC x) of
HsId(HsVar s) -> if elem s env then [] else [s]
HsInfixApp x (HsVar s) y -> if elem s env then [] else [s]
HsLeftSection x (HsVar s) -> if elem s env then [] else [s]
HsRightSection (HsVar s) x -> if elem s env then [] else [s]
x -> accE (++) (++) (++) (++) (++) x []
-- Return a pair of functions. The first is an env transformer, adding
-- the vars in the pattern, the second is a function given an env, which
-- determines the free vars in the pattern. The second is the constant []
-- function since patterns only introduce variables, they only have binding
-- occurences.
freeP :: HsPat -> ([HsName]->[HsName],[HsName]->[HsName])
freeP p = ((vs++),const [])
where vs = boundInP p []
-- Return a pair of functions. The first is an env transformer, adding
-- the vars declared by the list of Decls, the second is a function which
-- when given an env, determines the free vars in the Decls
freeD :: [HsDecl] -> ([HsName]->[HsName],[HsName]->[HsName])
freeD ds = (ext,free)
where bound = foldr add [] ds
ext env = bound ++ env
add (Dec (HsPatBind s p rhs ds)) env = boundInP p env
add (Dec (HsFunBind s ((HsMatch s2 nm ps rhs ds):_))) env = nm : env
add (Dec (HsDataDecl s ctx typats condecls derivings)) env =
getTyName (head typats) : env
add (Dec (HsTypeDecl s typats t)) env = getTyName (head typats) : env
add d env = env
getNameOfTypat (Typ x) =
case x of
HsTyApp l _ -> getNameOfTypat l
HsTyCon n -> n
HsTyVar n -> n
_ -> error "getNameOfTypat "
free env = (foldr (f env) [] ds) \\ bound
f env (Dec d) ans =
accD (++)(++)(++)(++)(++)(++)
(scopD env (mapD (\ x -> ( (freeE x))) freeP freeD freeT freeC freeTP d)) ans
ff env (Dec d) ans =
accD (++)(++)(++)(++)(++)(++)
(scopD env (mapD (\ x -> ( (freeE x))) freeP freeD freeT freeC freeTP d)) ans
instance Env [HsName] where
extClass n l a args env = env
extTconstr n l a b env = n:env
extTvar n env = n:env
extConstr n l a env = n:env
extVar n l env = n:env
extSig n l env = env
extMod n env = env
env0 = []
restrictTvar env = env
-- Given an environment holding bound variables, return the
-- free variables in the HsType
freeT :: HsType -> [HsName] -> [HsName]
freeT (Typ x) env =
case scopT env (mapT freeT x) of
HsTyCon n -> if elem n env then [] else [n]
HsTyVar n -> if elem n env then [] else [n]
x -> accT (union) x []
allFree :: HsType -> [HsName] -> [HsName]
allFree (Typ x) ans =
case x of
HsTyCon n -> union [n] ans
HsTyVar n -> union [n] ans
x -> accT allFree x ans
-- compute the free variables in a context.
freeC :: [HsType] -> [HsName] -> [HsName]
freeC x env = concat (map (\z -> freeT z env) x)
-- Type patterns are HsTYpes which act as binding occurences. Hence
-- they return a pair. First an env transformer, and Second a function
-- that given an env, computes the TypePatterns free variables. Like patterns
-- this always returns []
freeTP :: HsType -> ([HsName] -> [HsName],[HsName] -> [HsName])
freeTP x = (allFree x,const [])
{-
makeSCC ds env =
let (envtrans,_) = freeD ds
bound = envtrans []
oneD d = let (_,free) = freeD [d] in free env
oneBind d = let (envt,_) = freeD [d] in envt []
allFree = map oneD ds
allBound = map oneBind ds
in (allFree,allBound)
-}
--------------------------------------------------------------------------
-- Contexts
--------------------------------------------------------------------------
-- type patterns appear in 4 different contexts
data TPContext = DataLikeTP | ClassTP | InstTP | SigTP
instance Show TPContext where
show DataLikeTP = "type, data, or newtype declaration"
show ClassTP = "class declaration"
show InstTP = "instance declaration"
show SigTP = "type signature"
-----------------------------------------------------------------
-- Lists of declarations can appear in four different contexts
-- Only certain kinds of declarations are legal in some of these.
data DeclContext = TopDecl | ClassDecl | InstDecl | WhereLikeDecl deriving (Eq)
instance Show DeclContext where
show TopDecl = "top level"
show ClassDecl = "class declaration"
show InstDecl = "class declaration"
show WhereLikeDecl = "local declaration"
legal :: DeclContext -> HsDecl -> Maybe Error
legal context (d @ (Dec x)) =
let err context x = Just (srcloc x,
"Illegal "++ whatIs x ++" in " ++ show context)
in case (context,x) of
(TopDecl, any) -> Nothing
(ClassDecl, HsTypeSig _ _ _ _) -> Nothing
(ClassDecl, HsFunBind _ _) -> Nothing
(ClassDecl, HsPatBind _ (Pat(HsPId(HsVar _))) _ _) -> Nothing
(ClassDecl, any) -> err context x
(InstDecl, HsFunBind _ _) -> Nothing
(InstDecl, HsPatBind _ (Pat(HsPId(HsVar _))) _ _) -> Nothing
(InstDecl, any) -> err context x
(WhereLikeDecl, HsTypeSig _ _ _ _) -> Nothing
(WhereLikeDecl, HsFunBind _ _) -> Nothing
(WhereLikeDecl, HsPatBind _ _ _ _) -> Nothing
(WhereLikeDecl, any) -> err context x
-----------------------------------------------------------------------
-- MapD' is like mapD, except it know what kind of contexts are
-- appropriate and passes this information downwards
mapD' :: (a -> b) -> (c -> d) -> (DeclContext -> e -> f) -> (g -> h) -> (DeclContext -> i -> j)
-> (TPContext -> k -> l) -> D a c e g i k -> D b d f h j l
mapD' ef pf df tf cf tpf decl =
case decl of
HsTypeDecl s tps t ->
HsTypeDecl s (map (tpf DataLikeTP) tps) (tf t)
HsNewTypeDecl s cntxt tps cd names ->
HsNewTypeDecl s (cf TopDecl cntxt)
(map (tpf DataLikeTP) tps) (mapConDecl tf cd) names
HsDataDecl s cntxt tps cds names ->
HsDataDecl s (cf TopDecl cntxt)
(map (tpf DataLikeTP) tps)
(map (mapConDecl tf) cds) names
HsClassDecl s c tp ds ->
HsClassDecl s (cf ClassDecl c) (tpf ClassTP tp) (df ClassDecl ds)
HsInstDecl s c tp ds ->
HsInstDecl s (cf InstDecl c) (tpf InstTP tp) (df InstDecl ds)
HsDefaultDecl s t ->
HsDefaultDecl s (tf t)
HsTypeSig s nms c t ->
HsTypeSig s nms (cf TopDecl c) (tpf SigTP t)
HsFunBind s matches ->
HsFunBind s (map (mapMatch ef pf (df WhereLikeDecl)) matches)
HsPatBind s p rhs ds ->
HsPatBind s (pf p) (mapRhs ef rhs) (df WhereLikeDecl ds)
HsPrimitiveTypeDecl s cntxt nm ->
HsPrimitiveTypeDecl s (cf TopDecl cntxt) nm
HsPrimitiveBind s nm t ->
HsPrimitiveBind s nm (tf t) -- Hugs compatibility
{-
-------------------------------------------------------------------
-------------------------------------------------------------------
-- Static Checking using Bind based scoping
-------------------------------------------------------------------------
-- Example extend function for the static env Senv of the static checker
-- extTvar nm env = env {tvarNames = (nm) : tvarNames env}
extend :: Bind -> Senv -> Senv
extend (Bpat loc pat) env = foldr extName env uniqueNames
where (uniqueNames,dups,constrArities) = patBound pat ([],[],[])
extName nm env = env {varNames = (nm,loc) : varNames env}
extend (Bpats loc ps) env = foldr extend env (map (Bpat loc) ps)
extend (Bdecls ds) env = allNames ds env
extend (Bname loc nm) env = env {varNames = (nm,loc) : varNames env}
extend (Btypat tag tp) env =
case tag of
ClassTag -> -- (Env e x) -- expects (C v1 ... vn)
let (constr, tvs) = typePatToParts tp
in foldr extTvar env tvs
InstTag -> -- (Env [Int] Bool) -- expects (C t1 ... tn)
let (classname, ts) = instPatToParts tp
(tvs, cs) = foldr allTypNames ([], []) ts
in foldr extTvar env tvs
SigTag -> -- (e : typ)
let (tvs, cs) = allTypNames tp ([], [])
in foldr extTvar env tvs
extend (Btypats tag (tps @ (constr : args))) env =
case tag of
DataTPS -> foldr (\ t e -> extTvar (getTyName t) e) env tps
TypeTPS -> foldr (\ t e -> extTvar (getTyName t) e) env args
staticlib = Sc extend restrictTvar
------------------------------------------------------------------
-- Static checks for expressions
checkE :: SrcLoc -> HsExp -> Senv -> [Error]
checkE loc (exp @ (Exp x)) env =
case scopeE staticlib env
(mapE (checkE loc) (checkP loc)
(checkDs WhereLikeDecl) (checkT loc) (checkCnxt loc WhereLikeDecl) x) of
HsId (HsVar n) -> chk loc (not (varDefined n env)) (undefined_variable n)
HsInfixApp x (HsVar n) y -> chk loc (not (varDefined n env)) (undefined_variable n)
HsLeftSection x (HsVar n) -> chk loc (not (varDefined n env)) (undefined_variable n)
HsRightSection (HsVar n) x -> chk loc (not (varDefined n env)) (undefined_variable n)
HsLambda ps e -> e ++ (checkPList loc env ps)
z -> accE (++) (\ (nm,err) a -> err ++ a) (++) (++) (++) z []
-----------------------------------------------------------------------------
-- When language constructs have a list of patterns like : (\ p1 ... pn -> e)
-- or (case x of { C p1 ... pn -> e }), Haskell has the rule that no variable
-- should appear more than once in the list. We can't check this, pattern by
-- pattern, but have to observe the complete list. If we map (chP env) over a
-- list of patterns we get [([unique_names],[error_messages])], from this we
-- can compute additional error_messages dealing with duplicates.
checkPList :: SrcLoc -> Senv -> [([HsName],[Error])] -> [Error]
checkPList loc env ps =
let accumulate (ns,errs) (names,errors) = (ns++names,errs++errors)
(allbound,internalerr) = foldr accumulate ([],[]) ps
dups = duplicates allbound
duperr = chk loc (not (null dups)) (repeated_pattern_variables dups)
in internalerr ++ duperr
--------------------------------------------
-- Static checks for individual patterns
checkP :: SrcLoc -> HsPat -> (HsPat, Senv -> ([HsName],[Error]))
checkP loc (pat @ (Pat x)) = (pat, f)
where (uniqueNames,dups,constrArities) = patBound pat ([],[],[])
duperr = chk loc (not (null dups)) (duplicate_vars_in_pattern dups)
f env = (uniqueNames,allErrors env)
allErrors env = foldr arityCheck duperr constrArities
where arityCheck (c,n) ans = check c n (cArity c env) ++ ans
check c n Nothing = [(loc,undefined_constr c)]
check c n (Just m) = chk loc (m /=n) (constr_wrong_arity n c)
------------------------------------------------------------------------------
-- Static Check for Expressions
-- checkDs assumes that all the names in the [Decl] have already been added
-- to the environment which is passed to checkDs result function.
-- e.g. in scopeE for HsLet we say:
-- HsLet (ds,f) e ->
-- let env2 = ext (Bdecls ds) env
-- in HsLet (f env2) (e env2)
-- note how we compute the new env, and pass it to both the ds and the f
checkDs :: DeclContext -> [HsDecl] -> ([HsDecl],Senv -> [Error])
checkDs contxt ds = (ds,errorfun)
where env = allNames ds env0
errorfun env = foldr (\ d ans -> (check env d) ++ ans) allErrors ds
sameName (x,y) (a,b) = compare x a
contextErrors = catMaybes $ map (legal contxt) ds
dupErr k message = collect_duplicate_info (dupErrs message) sameName (locations k env)
dupValErrors = dupErr Var "value definitions"
dupSigErrors = dupErr Sig "type signatures"
dupClsErrors = dupErr Class "class definitions"
dupTypErrors = dupErr TyCons "type definitions"
dupConsErrors = dupErr Cons "constructor functions"
allErrors = contextErrors++dupValErrors++dupSigErrors++dupClsErrors
++ dupTypErrors ++ dupConsErrors ++ nmConflict env ++ clsMethodErr
sigerr loc name = chk loc ((not $ elem name (map fst (varNames env))) && contxt/=ClassDecl)
(signature_without_definition name)
methodErr c (nm,loc) = chk loc (not $ isMethod nm c env) (not_a_method nm c)
clsMethodErr = case contxt of
ClassDecl -> classMethodErr env
other -> []
check env (Dec x) =
let loc = srcloc x
methodErrs (HsInstDecl loc c tp ds) =
let nms = varNames $ allNames ds env0
in case getClass tp of
Nothing -> []
Just c -> concat $ map (methodErr c) nms
in
case scopeD staticlib env
(mapD' (checkE loc) (checkP loc) (checkDs)
(checkT loc) (checkCnxt loc) (checkTp loc) x) of
HsTypeSig loc nms c t -> (concat $ map (sigerr loc) nms)++c++t
HsInstDecl loc c tp ds -> methodErrs x ++ c ++ tp ++ ds
z -> accD (++) (\ (ns,errs) a -> (errs)++a) (++) (++) (++) (++) z []
---------------------------------------------------------------------------
-- static checks for types
checkT :: SrcLoc -> HsType -> Senv -> [Error]
checkT loc (typ @ (Typ t)) env =
case t of
HsTyVar nm -> chk loc (not (tvarDefined nm env)) (undefined_tvar nm)
HsTyCon nm -> chk loc (not (tconDefined nm env)) (undefined_tcon nm)
HsTyApp (y @ (Typ f)) x -> synArityCheck (checkT loc) env f x 1
z -> accT (++) (scopeT env (mapT (checkT loc) z)) []
synArityCheck chf env typ arg n =
case typ of
(HsTyCon c) ->
case synArity c env of
Nothing -> chk loc (not (tconDefined c env)) (undefined_tcon c) ++ chf arg env
Just m -> chk loc (m/=n) (tysynonym_not_fully_applied c) ++ chf arg env
(HsTyApp (Typ f) x) -> synArityCheck chf env f x (n+1) ++ chf arg env
t -> chf (Typ t) env ++ chf arg env
----------------------------------------------------------------------
-- Static Checking for contexts
checkCnxt :: SrcLoc -> DeclContext -> [HsType] -> Senv -> [Error]
checkCnxt loc c ts env = foldr (check c) [] ts
where inscope (Typ (HsTyVar x)) ans =
chk loc (not $ tvarDefined x env) (undefined_tvar_in_context x) ++ ans
inscope (Typ (HsTyCon c)) ans =
chk loc (not $ classDefined c env) (undefined_class_in_context c) ++ ans
inscope (Typ x) ans = accT inscope x ans
-- class: C (x t*)+
wfClass t (Typ (HsTyApp (Typ (HsTyCon c)) x )) xs =
wfClassArg x x xs
wfClass t (Typ (HsTyApp x y )) xs =
wfClass t x $ wfClassArg x x xs
wfClass t (Typ x) xs =
(loc, illformed_class t) : xs
-- class arg: x t*
wfClassArg t (Typ (HsTyVar y)) xs = xs
wfClassArg t (Typ (HsTyApp x _)) xs = wfClassArg t x xs
wfClassArg t (Typ x) xs = (loc, illformed_class_arg t) : xs
check ClassDecl x ans = wfSclass loc x (inscope x ans)
check InstDecl x ans = wfSclass loc x (inscope x ans)
check _ x ans = wfClass x x (inscope x ans)
---------------------------------------------------------------------
-- Static checks for type-patterns
--checkTp :: SrcLoc -> TPContext -> HsType -> (HsType,Senv -> [Error])
checkTp :: SrcLoc -> TPContext -> HsType -> (HsType, Senv -> [Error])
checkTp srcloc InstTP x =
let errors = wf x []
-- well formed instance: C (C x*)+
wf (Typ(HsTyApp (Typ(HsTyCon c)) arg)) xs =
wfTp srcloc InstTP arg xs
wf (Typ(HsTyCon c)) xs =
(srcloc, instance_required c) : xs
wf (Typ(HsTyApp y arg)) xs =
wf y (wfTp srcloc InstTP arg xs)
wf tp xs =
(srcloc, instance_not_class_app tp) : xs
(classname, ts) = instPatToParts x
(tvs, cs) = foldr allTypNames ([], []) ts
clsError env = chk srcloc (not $ classDefined classname env)
(undefined_class_in_instance classname)
cdef env c ans =
if tconDefined c env
then case synArity c env of
Nothing -> ans
Just _ -> (srcloc, synonym_illegal_in_instance c):ans
else (srcloc,undefined_tcon_in_instance c):ans
dupErrs = collect_duplicate_info (dupTvErr srcloc) compare tvs
tpf env = if null errors
then foldr (cdef env) (dupErrs ++ clsError env) cs
else errors
in (x, tpf)
checkTp srcloc SigTP x =
let (_, cs) = allTypNames x ([], [])
cdef env c ans =
if tconDefined c env
then ans
else (srcloc, undefined_tcon_in_signature c):ans
tpf env = foldr (cdef env) [] cs
in (x, tpf)
checkTp srcloc cntxt x =
let (_, tvs) = typePatToParts x
errors = case cntxt of DataLikeTP -> wfTp srcloc cntxt x []
ClassTP -> wfSclass srcloc x []
tpf env = if null errors
then collect_duplicate_info (dupTvErr srcloc) compare tvs
else errors
in (x, tpf)
-----------------------------------------------------------------
-- Running the basic tests
run2 env prog = let (ds,f) = checkDs TopDecl prog in (f (allNames ds env))
new (_,x) = run2 env0 x
old (_,x) = run env0 x
test2 :: (String,[HsDecl]) -> IO ()
test2 (s, ds) =
do { putStr "\n==============================================\n"
; putStr s
; putStr "\n--- test code----------\n"
; sh ds
; putStr "\n--- errors ------------\n"
; (putStr . unlines . map showErr . run2 env0) ds
}
tests2 ts = sequence_ (map test2 ts)
errors1 ts = map (run2 env0) (map snd ts)
errors2 ts = map (run env0) (map snd ts)
new1 = errors1 insts
old1 = errors2 insts
oks = zipWith (==) old1 new1
[x0,x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11] = insts
gg x = concat(map (\ (y,_,_,_) -> show y) (classNames x))
------------------------------------------------------------------
-- extra stuff
-- supply a unique integer string
count :: IORef Int
count = unsafePerformIO $ newIORef 0
initCount = writeIORef count 10
incCount a = unsafePerformIO $ do { c <- readIORef count
; writeIORef count $! (c+1)
; return c
}
uniqueStr a = show $ incCount ()
-}