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Idris-dev/src/Core/CaseTree.hs
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1{-# LANGUAGE PatternGuards, DeriveFunctor #-}
3module Core.CaseTree(CaseDef(..), SC, SC'(..), CaseAlt, CaseAlt'(..),
4 Phase(..), CaseTree,
5 simpleCase, small, namesUsed, findCalls, findUsedArgs) where
7import Core.TT
9import Control.Monad.State
10import Data.Maybe
11import Data.List hiding (partition)
12import Debug.Trace
14data CaseDef = CaseDef [Name] SC [Term]
15 deriving Show
17data SC' t = Case Name [CaseAlt' t] -- invariant: lowest tags first
18 | ProjCase t [CaseAlt' t] -- special case for projections
19 | STerm t
20 | UnmatchedCase String -- error message
21 | ImpossibleCase -- already checked to be impossible
22 deriving (Eq, Ord, Functor)
23{-!
24deriving instance Binary SC
25!-}
27type SC = SC' Term
29data CaseAlt' t = ConCase Name Int [Name] (SC' t)
30 | ConstCase Const (SC' t)
31 | DefaultCase (SC' t)
32 deriving (Show, Eq, Ord, Functor)
33{-!
34deriving instance Binary CaseAlt
35!-}
37type CaseAlt = CaseAlt' Term
39instance Show t => Show (SC' t) where
40 show sc = show' 1 sc
41 where
42 show' i (Case n alts) = "case " ++ show n ++ " of\n" ++ indent i ++
43 showSep ("\n" ++ indent i) (map (showA i) alts)
44 show' i (ProjCase tm alts) = "case " ++ show tm ++ " of " ++
45 showSep ("\n" ++ indent i) (map (showA i) alts)
46 show' i (STerm tm) = show tm
47 show' i (UnmatchedCase str) = "error " ++ show str
48 show' i ImpossibleCase = "impossible"
50 indent i = concat $ take i (repeat " ")
52 showA i (ConCase n t args sc)
53 = show n ++ "(" ++ showSep (", ") (map show args) ++ ") => "
54 ++ show' (i+1) sc
55 showA i (ConstCase t sc)
56 = show t ++ " => " ++ show' (i+1) sc
57 showA i (DefaultCase sc)
58 = "_ => " ++ show' (i+1) sc
61type CaseTree = SC
62type Clause = ([Pat], (Term, Term))
63type CS = ([Term], Int)
65instance TermSize SC where
66 termsize n (Case n' as) = termsize n as
67 termsize n (STerm t) = termsize n t
68 termsize n _ = 1
70instance TermSize CaseAlt where
71 termsize n (ConCase _ _ _ s) = termsize n s
72 termsize n (ConstCase _ s) = termsize n s
73 termsize n (DefaultCase s) = termsize n s
75-- simple terms can be inlined trivially - good for primitives in particular
76-- To avoid duplicating work, don't inline something which uses one
77-- of its arguments in more than one place
79small :: Name -> [Name] -> SC -> Bool
80small n args t = let as = findAllUsedArgs t args in
81 length as == length (nub as) &&
82 termsize n t < 20
84namesUsed :: SC -> [Name]
85namesUsed sc = nub $ nu' [] sc where
86 nu' ps (Case n alts) = nub (concatMap (nua ps) alts) \\ [n]
87 nu' ps (ProjCase t alts) = nub $ (nut ps t ++
88 (concatMap (nua ps) alts))
89 nu' ps (STerm t) = nub $ nut ps t
90 nu' ps _ = []
92 nua ps (ConCase n i args sc) = nub (nu' (ps ++ args) sc) \\ args
93 nua ps (ConstCase _ sc) = nu' ps sc
94 nua ps (DefaultCase sc) = nu' ps sc
96 nut ps (P _ n _) | n `elem` ps = []
97 | otherwise = [n]
98 nut ps (App f a) = nut ps f ++ nut ps a
99 nut ps (Proj t _) = nut ps t
100 nut ps (Bind n (Let t v) sc) = nut ps v ++ nut (n:ps) sc
101 nut ps (Bind n b sc) = nut (n:ps) sc
102 nut ps _ = []
104-- Return all called functions, and which arguments are used in each argument position
105-- for the call, in order to help reduce compilation time, and trace all unused
106-- arguments
108findCalls :: SC -> [Name] -> [(Name, [[Name]])]
109findCalls sc topargs = nub $ nu' topargs sc where
110 nu' ps (Case n alts) = nub (concatMap (nua (n : ps)) alts)
111 nu' ps (ProjCase t alts) = nub (nut ps t ++ concatMap (nua ps) alts)
112 nu' ps (STerm t) = nub $ nut ps t
113 nu' ps _ = []
115 nua ps (ConCase n i args sc) = nub (nu' (ps ++ args) sc)
116 nua ps (ConstCase _ sc) = nu' ps sc
117 nua ps (DefaultCase sc) = nu' ps sc
119 nut ps (P Ref n _) | n `elem` ps = []
120 | otherwise = [(n, [])] -- tmp
121 nut ps fn@(App f a)
122 | (P Ref n _, args) <- unApply fn
123 = if n `elem` ps then nut ps f ++ nut ps a
124 else [(n, map argNames args)] ++ concatMap (nut ps) args
125 | otherwise = nut ps f ++ nut ps a
126 nut ps (Bind n (Let t v) sc) = nut ps v ++ nut (n:ps) sc
127 nut ps (Proj t _) = nut ps t
128 nut ps (Bind n b sc) = nut (n:ps) sc
129 nut ps _ = []
131 argNames tm = let ns = directUse tm in
132 filter (\x -> x `elem` ns) topargs
134-- Find names which are used directly (i.e. not in a function call) in a term
136directUse :: Eq n => TT n -> [n]
137directUse (P _ n _) = [n]
138directUse (Bind n (Let t v) sc) = nub $ directUse v ++ (directUse sc \\ [n])
139 ++ directUse t
140directUse (Bind n b sc) = nub $ directUse (binderTy b) ++ (directUse sc \\ [n])
141directUse fn@(App f a)
142 | (P Ref n _, args) <- unApply fn = [] -- need to know what n does with them
143 | otherwise = nub $ directUse f ++ directUse a
144directUse (Proj x i) = nub $ directUse x
145directUse _ = []
147-- Find all directly used arguments (i.e. used but not in function calls)
149findUsedArgs :: SC -> [Name] -> [Name]
150findUsedArgs sc topargs = nub (findAllUsedArgs sc topargs)
152findAllUsedArgs sc topargs = filter (\x -> x `elem` topargs) (nu' sc) where
153 nu' (Case n alts) = n : concatMap nua alts
154 nu' (ProjCase t alts) = directUse t ++ concatMap nua alts
155 nu' (STerm t) = directUse t
156 nu' _ = []
158 nua (ConCase n i args sc) = nu' sc
159 nua (ConstCase _ sc) = nu' sc
160 nua (DefaultCase sc) = nu' sc
162data Phase = CompileTime | RunTime
163 deriving (Show, Eq)
165-- Generate a simple case tree
166-- Work Right to Left
168simpleCase :: Bool -> Bool -> Phase -> FC -> [([Name], Term, Term)] ->
169 TC CaseDef
170simpleCase tc cover phase fc []
171 = return $ CaseDef [] (UnmatchedCase "No pattern clauses") []
172simpleCase tc cover phase fc cs
173 = let proj = phase == RunTime
174 pats = map (\ (avs, l, r) ->
175 (avs, toPats tc l, (l, r))) cs
176 chkPats = mapM chkAccessible pats in
177 case chkPats of
178 OK pats ->
179 let numargs = length (fst (head pats))
180 ns = take numargs args
181 (ns', ps') = order ns pats
182 (tree, st) = runState
183 (match ns' ps' (defaultCase cover)) ([], numargs)
184 t = CaseDef ns (prune proj (depatt ns' tree)) (fst st) in
185 if proj then return (stripLambdas t) else return t
186 Error err -> Error (At fc err)
187 where args = map (\i -> MN i "e") [0..]
188 defaultCase True = STerm Erased
189 defaultCase False = UnmatchedCase "Error"
191 chkAccessible (avs, l, c)
192 | phase == RunTime = return (l, c)
193 | otherwise = do mapM_ (acc l) avs
194 return (l, c)
196 acc [] n = Error (Inaccessible n)
197 acc (PV x : xs) n | x == n = OK ()
198 acc (PCon _ _ ps : xs) n = acc (ps ++ xs) n
199 acc (_ : xs) n = acc xs n
201data Pat = PCon Name Int [Pat]
202 | PConst Const
203 | PV Name
204 | PAny
205 deriving Show
207-- If there are repeated variables, take the *last* one (could be name shadowing
208-- in a where clause, so take the most recent).
210toPats :: Bool -> Term -> [Pat]
211toPats tc f = reverse (toPat tc (getArgs f)) where
212 getArgs (App f a) = a : getArgs f
213 getArgs _ = []
215toPat :: Bool -> [Term] -> [Pat]
216toPat tc tms = evalState (mapM (\x -> toPat' x []) tms) []
217 where
218 toPat' (P (DCon t a) n _) args = do args' <- mapM (\x -> toPat' x []) args
219 return $ PCon n t args'
220 -- Typecase
221 toPat' (P (TCon t a) n _) args | tc
222 = do args' <- mapM (\x -> toPat' x []) args
223 return $ PCon n t args'
224 toPat' (Constant IType) [] | tc = return $ PCon (UN "Int") 1 []
225 toPat' (Constant FlType) [] | tc = return $ PCon (UN "Float") 2 []
226 toPat' (Constant ChType) [] | tc = return $ PCon (UN "Char") 3 []
227 toPat' (Constant StrType) [] | tc = return $ PCon (UN "String") 4 []
228 toPat' (Constant PtrType) [] | tc = return $ PCon (UN "Ptr") 5 []
229 toPat' (Constant BIType) [] | tc = return $ PCon (UN "Integer") 6 []
230 toPat' (Constant W8Type) [] | tc = return $ PCon (UN "Word8") 7 []
231 toPat' (Constant W16Type) [] | tc = return $ PCon (UN "Word16") 8 []
233 toPat' (P Bound n _) [] = do ns <- get
234 if n `elem` ns
235 then return PAny
236 else do put (n : ns)
237 return (PV n)
238 toPat' (App f a) args = toPat' f (a : args)
239 toPat' (Constant x) [] = return $ PConst x
240 toPat' _ _ = return PAny
243data Partition = Cons [Clause]
244 | Vars [Clause]
245 deriving Show
247isVarPat (PV _ : ps , _) = True
248isVarPat (PAny : ps , _) = True
249isVarPat _ = False
251isConPat (PCon _ _ _ : ps, _) = True
252isConPat (PConst _ : ps, _) = True
253isConPat _ = False
255partition :: [Clause] -> [Partition]
256partition [] = []
257partition ms@(m : _)
258 | isVarPat m = let (vars, rest) = span isVarPat ms in
259 Vars vars : partition rest
260 | isConPat m = let (cons, rest) = span isConPat ms in
261 Cons cons : partition rest
262partition xs = error $ "Partition " ++ show xs
264-- reorder the patterns so that the one with most distinct names
265-- comes next. Take rightmost first, otherwise (i.e. pick value rather
266-- than dependency)
268order :: [Name] -> [Clause] -> ([Name], [Clause])
269order [] cs = ([], cs)
270order ns [] = (ns, [])
271order ns cs = let patnames = transpose (map (zip ns) (map fst cs))
272 pats' = transpose (sortBy moreDistinct (reverse patnames)) in
273 (getNOrder pats', zipWith rebuild pats' cs)
274 where
275 getNOrder [] = error $ "Failed order on " ++ show (ns, cs)
276 getNOrder (c : _) = map fst c
278 rebuild patnames clause = (map snd patnames, snd clause)
280 moreDistinct xs ys = compare (numNames [] (map snd ys))
281 (numNames [] (map snd xs))
283 numNames xs (PCon n _ _ : ps)
284 | not (Left n `elem` xs) = numNames (Left n : xs) ps
285 numNames xs (PConst c : ps)
286 | not (Right c `elem` xs) = numNames (Right c : xs) ps
287 numNames xs (_ : ps) = numNames xs ps
288 numNames xs [] = length xs
290match :: [Name] -> [Clause] -> SC -- error case
291 -> State CS SC
292match [] (([], ret) : xs) err
293 = do (ts, v) <- get
294 put (ts ++ (map (fst.snd) xs), v)
295 case snd ret of
296 Impossible -> return ImpossibleCase
297 tm -> return $ STerm tm -- run out of arguments
298match vs cs err = do let ps = partition cs
299 mixture vs ps err
301mixture :: [Name] -> [Partition] -> SC -> State CS SC
302mixture vs [] err = return err
303mixture vs (Cons ms : ps) err = do fallthrough <- mixture vs ps err
304 conRule vs ms fallthrough
305mixture vs (Vars ms : ps) err = do fallthrough <- mixture vs ps err
306 varRule vs ms fallthrough
308data ConType = CName Name Int -- named constructor
309 | CConst Const -- constant, not implemented yet
311data Group = ConGroup ConType -- Constructor
312 [([Pat], Clause)] -- arguments and rest of alternative
314conRule :: [Name] -> [Clause] -> SC -> State CS SC
315conRule (v:vs) cs err = do groups <- groupCons cs
316 caseGroups (v:vs) groups err
318caseGroups :: [Name] -> [Group] -> SC -> State CS SC
319caseGroups (v:vs) gs err = do g <- altGroups gs
320 return $ Case v (sort g)
321 where
322 altGroups [] = return [DefaultCase err]
323 altGroups (ConGroup (CName n i) args : cs)
324 = do g <- altGroup n i args
325 rest <- altGroups cs
326 return (g : rest)
327 altGroups (ConGroup (CConst c) args : cs)
328 = do g <- altConstGroup c args
329 rest <- altGroups cs
330 return (g : rest)
332 altGroup n i gs = do (newArgs, nextCs) <- argsToAlt gs
333 matchCs <- match (newArgs ++ vs) nextCs err
334 return $ ConCase n i newArgs matchCs
335 altConstGroup n gs = do (_, nextCs) <- argsToAlt gs
336 matchCs <- match vs nextCs err
337 return $ ConstCase n matchCs
339argsToAlt :: [([Pat], Clause)] -> State CS ([Name], [Clause])
340argsToAlt [] = return ([], [])
341argsToAlt rs@((r, m) : rest)
342 = do newArgs <- getNewVars r
343 return (newArgs, addRs rs)
344 where
345 getNewVars [] = return []
346 getNewVars ((PV n) : ns) = do v <- getVar
347 nsv <- getNewVars ns
348 return (v : nsv)
349 getNewVars (_ : ns) = do v <- getVar
350 nsv <- getNewVars ns
351 return (v : nsv)
352 addRs [] = []
353 addRs ((r, (ps, res)) : rs) = ((r++ps, res) : addRs rs)
355 uniq i (UN n) = MN i n
356 uniq i n = n
358getVar :: State CS Name
359getVar = do (t, v) <- get; put (t, v+1); return (MN v "e")
361groupCons :: [Clause] -> State CS [Group]
362groupCons cs = gc [] cs
363 where
364 gc acc [] = return acc
365 gc acc ((p : ps, res) : cs) =
366 do acc' <- addGroup p ps res acc
367 gc acc' cs
368 addGroup p ps res acc = case p of
369 PCon con i args -> return $ addg con i args (ps, res) acc
370 PConst cval -> return $ addConG cval (ps, res) acc
371 pat -> fail $ show pat ++ " is not a constructor or constant (can't happen)"
373 addg con i conargs res [] = [ConGroup (CName con i) [(conargs, res)]]
374 addg con i conargs res (g@(ConGroup (CName n j) cs):gs)
375 | i == j = ConGroup (CName n i) (cs ++ [(conargs, res)]) : gs
376 | otherwise = g : addg con i conargs res gs
378 addConG con res [] = [ConGroup (CConst con) [([], res)]]
379 addConG con res (g@(ConGroup (CConst n) cs) : gs)
380 | con == n = ConGroup (CConst n) (cs ++ [([], res)]) : gs
381 | otherwise = g : addConG con res gs
383varRule :: [Name] -> [Clause] -> SC -> State CS SC
384varRule (v : vs) alts err =
385 do let alts' = map (repVar v) alts
386 match vs alts' err
387 where
388 repVar v (PV p : ps , (lhs, res)) = (ps, (lhs, subst p (P Bound v Erased) res))
389 repVar v (PAny : ps , res) = (ps, res)
391-- fix: case e of S k -> f (S k) ==> case e of S k -> f e
392depatt :: [Name] -> SC -> SC
393depatt ns tm = dp [] tm
394 where
395 dp ms (STerm tm) = STerm (applyMaps ms tm)
396 dp ms (Case x alts) = Case x (map (dpa ms x) alts)
397 dp ms sc = sc
399 dpa ms x (ConCase n i args sc)
400 = ConCase n i args (dp ((x, (n, args)) : ms) sc)
401 dpa ms x (ConstCase c sc) = ConstCase c (dp ms sc)
402 dpa ms x (DefaultCase sc) = DefaultCase (dp ms sc)
404 applyMaps ms f@(App _ _)
405 | (P nt cn pty, args) <- unApply f
406 = let args' = map (applyMaps ms) args in
407 applyMap ms nt cn pty args'
408 where
409 applyMap [] nt cn pty args' = mkApp (P nt cn pty) args'
410 applyMap ((x, (n, args)) : ms) nt cn pty args'
411 | and ((length args == length args') :
412 (n == cn) : zipWith same args args') = P Ref x Erased
413 | otherwise = applyMap ms nt cn pty args'
414 same n (P _ n' _) = n == n'
415 same _ _ = False
416 applyMaps ms (App f a) = App (applyMaps ms f) (applyMaps ms a)
417 applyMaps ms t = t
419prune :: Bool -> -- ^ Convert single branches to projections (only useful at runtime)
420 SC -> SC
421prune proj (Case n alts)
422 = let alts' = filter notErased (map pruneAlt alts) in
423 case alts' of
424 [] -> ImpossibleCase
425 as@[ConCase cn i args sc] -> if proj then mkProj n 0 args sc
426 else Case n as
427 as -> Case n as
428 where pruneAlt (ConCase cn i ns sc) = ConCase cn i ns (prune proj sc)
429 pruneAlt (ConstCase c sc) = ConstCase c (prune proj sc)
430 pruneAlt (DefaultCase sc) = DefaultCase (prune proj sc)
432 notErased (DefaultCase (STerm Erased)) = False
433 notErased (DefaultCase ImpossibleCase) = False
434 notErased _ = True
436 mkProj n i [] sc = sc
437 mkProj n i (x : xs) sc = mkProj n (i + 1) xs (projRep x n i sc)
439 projRep :: Name -> Name -> Int -> SC -> SC
440 projRep arg n i (Case x alts)
441 | x == arg = ProjCase (Proj (P Bound n Erased) i)
442 (map (projRepAlt arg n i) alts)
443 | otherwise = Case x (map (projRepAlt arg n i) alts)
444 projRep arg n i (ProjCase t alts)
445 = ProjCase (projRepTm arg n i t) (map (projRepAlt arg n i) alts)
446 projRep arg n i (STerm t) = STerm (projRepTm arg n i t)
447 projRep arg n i c = c -- unmatched
449 projRepAlt arg n i (ConCase cn t args rhs)
450 = ConCase cn t args (projRep arg n i rhs)
451 projRepAlt arg n i (ConstCase t rhs)
452 = ConstCase t (projRep arg n i rhs)
453 projRepAlt arg n i (DefaultCase rhs)
454 = DefaultCase (projRep arg n i rhs)
456 projRepTm arg n i t = subst arg (Proj (P Bound n Erased) i) t
458prune _ t = t
460stripLambdas :: CaseDef -> CaseDef
461stripLambdas (CaseDef ns (STerm (Bind x (Lam _) sc)) tm)
462 = stripLambdas (CaseDef (ns ++ [x]) (STerm (instantiate (P Bound x Erased) sc)) tm)
463stripLambdas x = x