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Idris-dev/src/Core/Execute.hs
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1{-# LANGUAGE PatternGuards, ExistentialQuantification #-}
2module Core.Execute (execute) where
4import Idris.AbsSyntax
5import Idris.AbsSyntaxTree
6import IRTS.Lang( IntTy(..)
7 , intTyToConst
8 , FType(..))
10import Idris.Primitives(Prim(..), primitives)
12import Core.TT
13import Core.Evaluate
14import Core.CaseTree
16import Debug.Trace
18import Util.DynamicLinker
19import Util.System
21import Control.Applicative hiding (Const)
22import Control.Monad.Trans
23import Control.Monad.Trans.State.Strict
24import Control.Monad.Trans.Error
25import Control.Monad
26import Data.Maybe
27import Data.Bits
28import qualified Data.Map as M
30import Foreign.LibFFI
31import Foreign.C.String
32import Foreign.Marshal.Alloc (free)
33import Foreign.Ptr
35import System.IO
37readMay :: (Read a) => String -> Maybe a
38readMay s = case reads s of
39 [(x, "")] -> Just x
40 _ -> Nothing
42data Lazy = Delayed ExecEnv Context Term | Forced ExecVal deriving Show
44data ExecState = ExecState { exec_thunks :: M.Map Int Lazy -- ^ Thunks - the result of evaluating "lazy" or calling lazy funcs
45 , exec_next_thunk :: Int -- ^ Ensure thunk key uniqueness
46 , exec_implicits :: Ctxt [PArg] -- ^ Necessary info on laziness from idris monad
47 , exec_dynamic_libs :: [DynamicLib] -- ^ Dynamic libs from idris monad
48 }
50data ExecVal = EP NameType Name ExecVal
51 | EV Int
52 | EBind Name (Binder ExecVal) (ExecVal -> Exec ExecVal)
53 | EApp ExecVal ExecVal
54 | EType UExp
55 | EErased
56 | EConstant Const
57 | forall a. EPtr (Ptr a)
58 | EThunk Int
59 | EHandle Handle
61instance Show ExecVal where
62 show (EP _ n _) = show n
63 show (EV i) = "!!V" ++ show i ++ "!!"
64 show (EBind n b body) = "EBind " ++ show b ++ " <<fn>>"
65 show (EApp e1 e2) = show e1 ++ " (" ++ show e2 ++ ")"
66 show (EType _) = "Type"
67 show EErased = "[__]"
68 show (EConstant c) = show c
69 show (EPtr p) = "<<ptr " ++ show p ++ ">>"
70 show (EThunk i) = "<<thunk " ++ show i ++ ">>"
71 show (EHandle h) = "<<handle " ++ show h ++ ">>"
73toTT :: ExecVal -> Exec Term
74toTT (EP nt n ty) = (P nt n) <$> (toTT ty)
75toTT (EV i) = return $ V i
76toTT (EBind n b body) = do body' <- body $ EP Bound n EErased
77 b' <- fixBinder b
78 Bind n b' <$> toTT body'
79 where fixBinder (Lam t) = Lam <$> toTT t
80 fixBinder (Pi t) = Pi <$> toTT t
81 fixBinder (Let t1 t2) = Let <$> toTT t1 <*> toTT t2
82 fixBinder (NLet t1 t2) = NLet <$> toTT t1 <*> toTT t2
83 fixBinder (Hole t) = Hole <$> toTT t
84 fixBinder (GHole t) = GHole <$> toTT t
85 fixBinder (Guess t1 t2) = Guess <$> toTT t1 <*> toTT t2
86 fixBinder (PVar t) = PVar <$> toTT t
87 fixBinder (PVTy t) = PVTy <$> toTT t
88toTT (EApp e1 e2) = do e1' <- toTT e1
89 e2' <- toTT e2
90 return $ App e1' e2'
91toTT (EType u) = return $ TType u
92toTT EErased = return Erased
93toTT (EConstant c) = return (Constant c)
94toTT (EThunk i) = return (P (DCon 0 0) (MN i "THUNK") Erased) --(force i) >>= toTT
95toTT (EHandle _) = return Erased
97unApplyV :: ExecVal -> (ExecVal, [ExecVal])
98unApplyV tm = ua [] tm
99 where ua args (EApp f a) = ua (a:args) f
100 ua args t = (t, args)
102mkEApp :: ExecVal -> [ExecVal] -> ExecVal
103mkEApp f [] = f
104mkEApp f (a:args) = mkEApp (EApp f a) args
106initState :: Idris ExecState
107initState = do ist <- getIState
108 return $ ExecState M.empty 0 (idris_implicits ist) (idris_dynamic_libs ist)
110type Exec = ErrorT String (StateT ExecState IO)
112runExec :: Exec a -> ExecState -> IO (Either String a)
113runExec ex st = fst <$> runStateT (runErrorT ex) st
115getExecState :: Exec ExecState
116getExecState = lift get
118putExecState :: ExecState -> Exec ()
119putExecState = lift . put
121execFail :: String -> Exec a
122execFail = throwError
124execIO :: IO a -> Exec a
125execIO = lift . lift
127delay :: ExecEnv -> Context -> Term -> Exec ExecVal
128delay env ctxt tm =
129 do st <- getExecState
130 let i = exec_next_thunk st
131 putExecState $ st { exec_thunks = M.insert i (Delayed env ctxt tm) (exec_thunks st)
132 , exec_next_thunk = exec_next_thunk st + 1
133 }
134 return $ EThunk i
136force :: Int -> Exec ExecVal
137force i = do st <- getExecState
138 case M.lookup i (exec_thunks st) of
139 Just (Delayed env ctxt tm) -> do tm' <- doExec env ctxt tm
140 case tm' of
141 EThunk i ->
142 do res <- force i
143 update res i
144 return res
145 _ -> do update tm' i
146 return tm'
147 Just (Forced tm) -> return tm
148 Nothing -> execFail "Tried to exec non-existing thunk. This is a bug!"
149 where update :: ExecVal -> Int -> Exec ()
150 update tm i = do est <- getExecState
151 putExecState $ est { exec_thunks = M.insert i (Forced tm) (exec_thunks est) }
153tryForce :: ExecVal -> Exec ExecVal
154tryForce (EThunk i) = force i
155tryForce tm = return tm
157debugThunks :: Exec ()
158debugThunks = do st <- getExecState
159 execIO $ putStrLn (take 4000 (show (exec_thunks st)))
161execute :: Term -> Idris Term
162execute tm = do est <- initState
163 ctxt <- getContext
164 res <- lift $ flip runExec est $ do res <- doExec [] ctxt tm
165 toTT res
166 case res of
167 Left err -> fail err
168 Right tm' -> return tm'
170ioWrap :: ExecVal -> ExecVal
171ioWrap tm = mkEApp (EP (DCon 0 2) (UN "prim__IO") EErased) [EErased, tm]
173ioUnit :: ExecVal
174ioUnit = ioWrap (EP Ref unitCon EErased)
176type ExecEnv = [(Name, ExecVal)]
178doExec :: ExecEnv -> Context -> Term -> Exec ExecVal
179doExec env ctxt p@(P Ref n ty) | Just v <- lookup n env = return v
180doExec env ctxt p@(P Ref n ty) =
181 do let val = lookupDef n ctxt
182 case val of
183 [Function _ tm] -> doExec env ctxt tm
184 [TyDecl _ _] -> return (EP Ref n EErased) -- abstract def
185 [Operator tp arity op] -> return (EP Ref n EErased) -- will be special-cased later
186 [CaseOp _ _ _ _ _ [] (STerm tm) _ _] -> -- nullary fun
187 doExec env ctxt tm
188 [CaseOp _ _ _ _ _ ns sc _ _] -> return (EP Ref n EErased)
189 [] -> execFail $ "Could not find " ++ show n ++ " in definitions."
190 thing -> trace (take 200 $ "got to " ++ show thing ++ " lookup up " ++ show n) $ undefined
191doExec env ctxt p@(P Bound n ty) =
192 case lookup n env of
193 Nothing -> execFail "not found"
194 Just tm -> return tm
195doExec env ctxt (P (DCon a b) n _) = return (EP (DCon a b) n EErased)
196doExec env ctxt (P (TCon a b) n _) = return (EP (TCon a b) n EErased)
197doExec env ctxt v@(V i) | i < length env = return (snd (env !! i))
198 | otherwise = execFail "env too small"
199doExec env ctxt (Bind n (Let t v) body) = do v' <- doExec env ctxt v
200 doExec ((n, v'):env) ctxt body
201doExec env ctxt (Bind n (NLet t v) body) = trace "NLet" $ undefined
202doExec env ctxt tm@(Bind n b body) = return $
203 EBind n (fmap (\_->EErased) b)
204 (\arg -> doExec ((n, arg):env) ctxt body)
205doExec env ctxt a@(App _ _) = execApp env ctxt (unApply a)
206doExec env ctxt (Constant c) = return (EConstant c)
207doExec env ctxt (Proj tm i) = let (x, xs) = unApply tm in
208 doExec env ctxt ((x:xs) !! i)
209doExec env ctxt Erased = return EErased
210doExec env ctxt Impossible = fail "Tried to execute an impossible case"
211doExec env ctxt (TType u) = return (EType u)
213execApp :: ExecEnv -> Context -> (Term, [Term]) -> Exec ExecVal
214execApp env ctxt (f, args) = do newF <- doExec env ctxt f
215 laziness <- (++ repeat False) <$> (getLaziness newF)
216 newArgs <- mapM argExec (zip args laziness)
217 execApp' env ctxt newF newArgs
218 where getLaziness (EP _ (UN "lazy") _) = return [False, True]
219 getLaziness (EP _ n _) = do est <- getExecState
220 let argInfo = exec_implicits est
221 case lookupCtxtName n argInfo of
222 [] -> return (repeat False)
223 [ps] -> return $ map lazyarg (snd ps)
224 many -> execFail $ "Ambiguous " ++ show n ++ ", found " ++ (take 200 $ show many)
225 getLaziness _ = return (repeat False) -- ok due to zip above
226 argExec :: (Term, Bool) -> Exec ExecVal
227 argExec (tm, False) = doExec env ctxt tm
228 argExec (tm, True) = delay env ctxt tm
231execApp' :: ExecEnv -> Context -> ExecVal -> [ExecVal] -> Exec ExecVal
232execApp' env ctxt v [] = return v -- no args is just a constant! can result from function calls
233execApp' env ctxt (EP _ (UN "unsafePerformIO") _) (ty:action:rest) | (prim__IO, [_, v]) <- unApplyV action =
234 execApp' env ctxt v rest
236execApp' env ctxt (EP _ (UN "io_bind") _) args@(_:_:v:k:rest) | (prim__IO, [_, v']) <- unApplyV v =
237 do v'' <- tryForce v'
238 res <- execApp' env ctxt k [v''] >>= tryForce
239 execApp' env ctxt res rest
240execApp' env ctxt con@(EP _ (UN "io_return") _) args@(tp:v:rest) =
241 do v' <- tryForce v
242 execApp' env ctxt (mkEApp con [tp, v']) rest
244-- Special cases arising from not having access to the C RTS in the interpreter
245execApp' env ctxt (EP _ (UN "mkForeign") _) (_:fn:EConstant (Str arg):rest)
246 | Just (FFun "putStr" _ _) <- foreignFromTT fn = do execIO (putStr arg)
247 execApp' env ctxt ioUnit rest
248execApp' env ctxt (EP _ (UN "mkForeign") _) (_:fn:EConstant (Str f):EConstant (Str mode):rest)
249 | Just (FFun "fileOpen" _ _) <- foreignFromTT fn = do m <- case mode of
250 "r" -> return ReadMode
251 "w" -> return WriteMode
252 "a" -> return AppendMode
253 "rw" -> return ReadWriteMode
254 "wr" -> return ReadWriteMode
255 "r+" -> return ReadWriteMode
256 _ -> execFail ("Invalid mode for " ++ f ++ ": " ++ mode)
257 h <- execIO $ openFile f m
258 execApp' env ctxt (ioWrap (EHandle h)) rest
260execApp' env ctxt (EP _ (UN "mkForeign") _) (_:fn:(EHandle h):rest)
261 | Just (FFun "fileEOF" _ _) <- foreignFromTT fn = do eofp <- execIO $ hIsEOF h
262 let res = ioWrap (EConstant (I $ if eofp then 1 else 0))
263 execApp' env ctxt res rest
265execApp' env ctxt (EP _ (UN "mkForeign") _) (_:fn:(EHandle h):rest)
266 | Just (FFun "fileClose" _ _) <- foreignFromTT fn = do execIO $ hClose h
267 execApp' env ctxt ioUnit rest
269execApp' env ctxt (EP _ (UN "mkForeign") _) (_:fn:(EPtr p):rest)
270 | Just (FFun "isNull" _ _) <- foreignFromTT fn = let res = ioWrap . EConstant . I $
271 if p == nullPtr then 1 else 0
272 in execApp' env ctxt res rest
274execApp' env ctxt f@(EP _ (UN "mkForeign") _) args@(ty:fn:xs) | Just (FFun f argTs retT) <- foreignFromTT fn
275 , length xs >= length argTs =
276 do res <- stepForeign (ty:fn:take (length argTs) xs)
277 case res of
278 Nothing -> fail $ "Could not call foreign function \"" ++ f ++
279 "\" with args " ++ show (take (length argTs) xs)
280 Just r -> return (mkEApp r (drop (length argTs) xs))
281 | otherwise = return (mkEApp f args)
283execApp' env ctxt c@(EP (DCon _ arity) n _) args =
284 do args' <- mapM tryForce (take arity args)
285 let restArgs = drop arity args
286 execApp' env ctxt (mkEApp c args') restArgs
288execApp' env ctxt c@(EP (TCon _ arity) n _) args =
289 do args' <- mapM tryForce (take arity args)
290 let restArgs = drop arity args
291 execApp' env ctxt (mkEApp c args') restArgs
293execApp' env ctxt f@(EP _ n _) args =
294 do let val = lookupDef n ctxt
295 case val of
296 [Function _ tm] -> fail "should already have been eval'd"
297 [TyDecl nt ty] -> return $ mkEApp f args
298 [Operator tp arity op] ->
299 if length args >= arity
300 then do args' <- mapM tryForce $ take arity args
301 case getOp n args' of
302 Just res -> do r <- res
303 execApp' env ctxt r (drop arity args)
304 Nothing -> return (mkEApp f args)
305 else return (mkEApp f args)
306 [CaseOp _ _ _ _ _ [] (STerm tm) _ _] -> -- nullary fun
307 do rhs <- doExec env ctxt tm
308 execApp' env ctxt rhs args
309 [CaseOp _ _ _ _ _ ns sc _ _] ->
310 do res <- execCase env ctxt ns sc args
311 return $ fromMaybe (mkEApp f args) res
312 thing -> return $ mkEApp f args
313execApp' env ctxt bnd@(EBind n b body) (arg:args) = do ret <- body arg
314 let (f', as) = unApplyV ret
315 execApp' env ctxt f' (as ++ args)
316execApp' env ctxt (EThunk i) args = do f <- force i
317 execApp' env ctxt f args
318execApp' env ctxt app@(EApp _ _) args2 | (f, args1) <- unApplyV app = execApp' env ctxt f (args1 ++ args2)
319execApp' env ctxt f args = return (mkEApp f args)
321-- | Look up primitive operations in the global table and transform them into ExecVal functions
322getOp :: Name -> [ExecVal] -> Maybe (Exec ExecVal)
323getOp (UN "prim__believe_me") [_, _, x] = Just (return x)
324getOp (UN "prim__readString") [EP _ (UN "prim__stdin") _] =
325 Just $ do line <- execIO getLine
326 return (EConstant (Str line))
327getOp (UN "prim__readString") [EHandle h] =
328 Just $ do contents <- execIO $ hGetLine h
329 return (EConstant (Str (contents ++ "\n")))
330getOp n args = getPrim n primitives >>= flip applyPrim args
331 where getPrim :: Name -> [Prim] -> Maybe ([ExecVal] -> Maybe ExecVal)
332 getPrim n [] = Nothing
333 getPrim n ((Prim pn _ arity def _ _) : prims) | n == pn = Just $ execPrim def
334 | otherwise = getPrim n prims
336 execPrim :: ([Const] -> Maybe Const) -> [ExecVal] -> Maybe ExecVal
337 execPrim f args = EConstant <$> (mapM getConst args >>= f)
339 getConst (EConstant c) = Just c
340 getConst _ = Nothing
342 applyPrim :: ([ExecVal] -> Maybe ExecVal) -> [ExecVal] -> Maybe (Exec ExecVal)
343 applyPrim fn args = return <$> fn args
348-- | Overall wrapper for case tree execution. If there are enough arguments, it takes them,
349-- evaluates them, then begins the checks for matching cases.
350execCase :: ExecEnv -> Context -> [Name] -> SC -> [ExecVal] -> Exec (Maybe ExecVal)
351execCase env ctxt ns sc args =
352 let arity = length ns in
353 if arity <= length args
354 then do let amap = zip ns args
355-- trace ("Case " ++ show sc ++ "\n in " ++ show amap ++"\n in env " ++ show env ++ "\n\n" ) $ return ()
356 caseRes <- execCase' env ctxt amap sc
357 case caseRes of
358 Just res -> Just <$> execApp' (map (\(n, tm) -> (n, tm)) amap ++ env) ctxt res (drop arity args)
359 Nothing -> return Nothing
360 else return Nothing
362-- | Take bindings and a case tree and examines them, executing the matching case if possible.
363execCase' :: ExecEnv -> Context -> [(Name, ExecVal)] -> SC -> Exec (Maybe ExecVal)
364execCase' env ctxt amap (UnmatchedCase _) = return Nothing
365execCase' env ctxt amap (STerm tm) =
366 Just <$> doExec (map (\(n, v) -> (n, v)) amap ++ env) ctxt tm
367execCase' env ctxt amap (Case n alts) | Just tm <- lookup n amap =
368 do tm' <- tryForce tm
369 case chooseAlt tm' alts of
370 Just (newCase, newBindings) ->
371 let amap' = newBindings ++ (filter (\(x,_) -> not (elem x (map fst newBindings))) amap) in
372 execCase' env ctxt amap' newCase
373 Nothing -> return Nothing
375chooseAlt :: ExecVal -> [CaseAlt] -> Maybe (SC, [(Name, ExecVal)])
376chooseAlt _ (DefaultCase sc : alts) = Just (sc, [])
377chooseAlt (EConstant c) (ConstCase c' sc : alts) | c == c' = Just (sc, [])
378chooseAlt tm (ConCase n i ns sc : alts) | ((EP _ cn _), args) <- unApplyV tm
379 , cn == n = Just (sc, zip ns args)
380 | otherwise = chooseAlt tm alts
381chooseAlt tm (_:alts) = chooseAlt tm alts
382chooseAlt _ [] = Nothing
387idrisType :: FType -> ExecVal
388idrisType FUnit = EP Ref unitTy EErased
389idrisType ft = EConstant (idr ft)
390 where idr (FInt ty) = intTyToConst ty
391 idr FDouble = FlType
392 idr FChar = ChType
393 idr FString = StrType
394 idr FPtr = PtrType
396data Foreign = FFun String [FType] FType deriving Show
399call :: Foreign -> [ExecVal] -> Exec (Maybe ExecVal)
400call (FFun name argTypes retType) args =
401 do fn <- findForeign name
402 case fn of
403 Nothing -> return Nothing
404 Just f -> do res <- call' f args retType
405 return . Just . ioWrap $ res
406 where call' :: ForeignFun -> [ExecVal] -> FType -> Exec ExecVal
407 call' (Fun _ h) args (FInt ITNative) = do res <- execIO $ callFFI h retCInt (prepArgs args)
408 return (EConstant (I (fromIntegral res)))
409 call' (Fun _ h) args (FInt IT8) = do res <- execIO $ callFFI h retCChar (prepArgs args)
410 return (EConstant (B8 (fromIntegral res)))
411 call' (Fun _ h) args (FInt IT16) = do res <- execIO $ callFFI h retCWchar (prepArgs args)
412 return (EConstant (B16 (fromIntegral res)))
413 call' (Fun _ h) args (FInt IT32) = do res <- execIO $ callFFI h retCInt (prepArgs args)
414 return (EConstant (B32 (fromIntegral res)))
415 call' (Fun _ h) args (FInt IT64) = do res <- execIO $ callFFI h retCLong (prepArgs args)
416 return (EConstant (B64 (fromIntegral res)))
417 call' (Fun _ h) args FDouble = do res <- execIO $ callFFI h retCDouble (prepArgs args)
418 return (EConstant (Fl (realToFrac res)))
419 call' (Fun _ h) args FChar = do res <- execIO $ callFFI h retCChar (prepArgs args)
420 return (EConstant (Ch (castCCharToChar res)))
421 call' (Fun _ h) args FString = do res <- execIO $ callFFI h retCString (prepArgs args)
422 hStr <- execIO $ peekCString res
423-- lift $ free res
424 return (EConstant (Str hStr))
426 call' (Fun _ h) args FPtr = do res <- execIO $ callFFI h (retPtr retVoid) (prepArgs args)
427 return (EPtr res)
428 call' (Fun _ h) args FUnit = do res <- execIO $ callFFI h retVoid (prepArgs args)
429 return (EP Ref unitCon EErased)
430-- call' (Fun _ h) args other = fail ("Unsupported foreign return type " ++ show other)
433 prepArgs = map prepArg
434 prepArg (EConstant (I i)) = argCInt (fromIntegral i)
435 prepArg (EConstant (B8 i)) = argCChar (fromIntegral i)
436 prepArg (EConstant (B16 i)) = argCWchar (fromIntegral i)
437 prepArg (EConstant (B32 i)) = argCInt (fromIntegral i)
438 prepArg (EConstant (B64 i)) = argCLong (fromIntegral i)
439 prepArg (EConstant (Fl f)) = argCDouble (realToFrac f)
440 prepArg (EConstant (Ch c)) = argCChar (castCharToCChar c) -- FIXME - castCharToCChar only safe for first 256 chars
441 prepArg (EConstant (Str s)) = argString s
442 prepArg (EPtr p) = argPtr p
443 prepArg other = trace ("Could not use " ++ take 100 (show other) ++ " as FFI arg.") undefined
447foreignFromTT :: ExecVal -> Maybe Foreign
448foreignFromTT t = case (unApplyV t) of
449 (_, [(EConstant (Str name)), args, ret]) ->
450 do argTy <- unEList args
451 argFTy <- sequence $ map getFTy argTy
452 retFTy <- getFTy ret
453 return $ FFun name argFTy retFTy
454 _ -> trace "failed to construct ffun" Nothing
456getFTy :: ExecVal -> Maybe FType
457getFTy (EApp (EP _ (UN "FIntT") _) (EP _ (UN intTy) _)) =
458 case intTy of
459 "ITNative" -> Just $ FInt ITNative
460 "IT8" -> Just $ FInt IT8
461 "IT16" -> Just $ FInt IT16
462 "IT32" -> Just $ FInt IT32
463 "IT64" -> Just $ FInt IT64
464 _ -> Nothing
465getFTy (EP _ (UN t) _) =
466 case t of
467 "FFloat" -> Just FDouble
468 "FChar" -> Just FChar
469 "FString" -> Just FString
470 "FPtr" -> Just FPtr
471 "FUnit" -> Just FUnit
472 _ -> Nothing
473getFTy _ = Nothing
475unList :: Term -> Maybe [Term]
476unList tm = case unApply tm of
477 (nil, [_]) -> Just []
478 (cons, ([_, x, xs])) ->
479 do rest <- unList xs
480 return $ x:rest
481 (f, args) -> Nothing
483unEList :: ExecVal -> Maybe [ExecVal]
484unEList tm = case unApplyV tm of
485 (nil, [_]) -> Just []
486 (cons, ([_, x, xs])) ->
487 do rest <- unEList xs
488 return $ x:rest
489 (f, args) -> Nothing
492toConst :: Term -> Maybe Const
493toConst (Constant c) = Just c
494toConst _ = Nothing
496stepForeign :: [ExecVal] -> Exec (Maybe ExecVal)
497stepForeign (ty:fn:args) = do let ffun = foreignFromTT fn
498 f' <- case (call <$> ffun) of
499 Just f -> f args
500 Nothing -> return Nothing
501 return f'
502stepForeign _ = fail "Tried to call foreign function that wasn't mkForeign"
504mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]
505mapMaybeM f [] = return []
506mapMaybeM f (x:xs) = do rest <- mapMaybeM f xs
507 x' <- f x
508 case x' of
509 Just x'' -> return (x'':rest)
510 Nothing -> return rest
512findForeign :: String -> Exec (Maybe ForeignFun)
513findForeign fn = do est <- getExecState
514 let libs = exec_dynamic_libs est
515 fns <- mapMaybeM getFn libs
516 case fns of
517 [f] -> return (Just f)
518 [] -> do execIO . putStrLn $ "Symbol \"" ++ fn ++ "\" not found"
519 return Nothing
520 fs -> do execIO . putStrLn $ "Symbol \"" ++ fn ++ "\" is ambiguous. Found " ++
521 show (length fs) ++ " occurrences."
522 return Nothing
523 where getFn lib = execIO $ catchIO (tryLoadFn fn lib) (\_ -> return Nothing)