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implement measured patterns

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This commit is contained in:
krangelov
2021-09-29 13:26:06 +02:00
parent 2137324f81
commit edd7081dea
12 changed files with 81 additions and 94 deletions
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55
src/compiler/GF/Compile/Compute/Concrete.hs
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@@ -25,6 +25,7 @@ import Control.Applicative
import qualified Control.Monad.Fail as Fail import qualified Control.Monad.Fail as Fail
import qualified Data.Map as Map import qualified Data.Map as Map
import GF.Text.Pretty import GF.Text.Pretty
import Debug.Trace
-- * Main entry points -- * Main entry points
@@ -151,13 +152,15 @@ patternMatch v0 ((env0,ps,args0,t):eqs) = match env0 ps eqs args0
| s1 == s2 -> match env ps eqs args | s1 == s2 -> match env ps eqs args
(PString s1, VC []) (PString s1, VC [])
| null s1 -> match env ps eqs args | null s1 -> match env ps eqs args
(PSeq p1 p2,VStr s) (PSeq min1 max1 p1 min2 max2 p2,v)
-> do eqs <- matchStr env (p1:p2:ps) eqs [] [] s [] args -> case value2string v of
patternMatch v0 eqs Just s -> do let n = length s
(PSeq p1 p2,VC vs)-> do mb_eqs <- matchSeq env (p1:p2:ps) eqs [] vs args lo = min1 `max` (n-max2)
case mb_eqs of hi = (n-min2) `min` max1
Just eqs -> patternMatch v0 eqs (ds,cs) = splitAt lo s
Nothing -> return v0 eqs <- matchStr env (p1:p2:ps) eqs (hi-lo) (reverse ds) cs args
patternMatch v0 eqs
Nothing -> return v0
(PChar, VStr [_]) -> match env ps eqs args (PChar, VStr [_]) -> match env ps eqs args
(PChars cs, VStr [c]) (PChars cs, VStr [c])
| elem c cs -> match env ps eqs args | elem c cs -> match env ps eqs args
@@ -173,29 +176,29 @@ patternMatch v0 ((env0,ps,args0,t):eqs) = match env0 ps eqs args0
Just tnk -> matchRec env pas as (p:ps) eqs (tnk:args) Just tnk -> matchRec env pas as (p:ps) eqs (tnk:args)
Nothing -> evalError ("Missing value for label" <+> pp lbl) Nothing -> evalError ("Missing value for label" <+> pp lbl)
matchSeq env ps eqs ws [] args = return (Just eqs) value2string (VStr s) = Just s
matchSeq env ps eqs ws (v:vs) args = do value2string (VC vs) = fmap unwords (mapM value2string vs)
mb_eqs <- matchSeq env ps eqs (v:ws) vs args value2string _ = Nothing
case v of
VStr [] -> return mb_eqs
VStr (c:cs) -> case mb_eqs of
Just eqs -> do eqs <- matchStr env ps eqs ws [c] cs vs args
return (Just eqs)
Nothing -> return Nothing
_ -> return Nothing
matchStr env ps eqs ws ds [] vs args = do matchStr env ps eqs i ds [] args = do
arg1 <- newEvaluatedThunk (vc (reverse (VStr (reverse ds):ws))) arg1 <- newEvaluatedThunk (vc (reverse ds))
arg2 <- newEvaluatedThunk (vc vs) arg2 <- newEvaluatedThunk (vc [])
return ((env,ps,arg1:arg2:args,t) : eqs) return ((env,ps,arg1:arg2:args,t) : eqs)
matchStr env ps eqs ws ds (c:cs) vs args = do matchStr env ps eqs 0 ds cs args = do
arg1 <- newEvaluatedThunk (vc (reverse (if null ds then ws else VStr (reverse ds):ws))) arg1 <- newEvaluatedThunk (vc (reverse ds))
arg2 <- newEvaluatedThunk (vc (VStr (c:cs):vs)) arg2 <- newEvaluatedThunk (vc cs)
eqs <- matchStr env ps eqs ws (c:ds) cs vs args return ((env,ps,arg1:arg2:args,t) : eqs)
matchStr env ps eqs i ds (c:cs) args = do
arg1 <- newEvaluatedThunk (vc (reverse ds))
arg2 <- newEvaluatedThunk (vc (c:cs))
eqs <- matchStr env ps eqs (i-1 :: Int) (c:ds) cs args
return ((env,ps,arg1:arg2:args,t) : eqs) return ((env,ps,arg1:arg2:args,t) : eqs)
vc [x] = x vc s =
vc xs = VC xs case words s of
[] -> VC []
[w] -> VStr w
ws -> VC (map VStr ws)
value2term i (VApp q tnks) = value2term i (VApp q tnks) =
foldM (\e1 tnk -> fmap (App e1) (force tnk [] >>= value2term i)) (QC q) tnks foldM (\e1 tnk -> fmap (App e1) (force tnk [] >>= value2term i)) (QC q) tnks

2
src/compiler/GF/Compile/GeneratePMCFG.hs
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@@ -385,7 +385,7 @@ convertTerm opts sel ctype (Alts s alts)= do CStr s <- convertTerm opts CNil cty
getPatts p = case p of getPatts p = case p of
PAlt a b -> liftM2 (++) (getPatts a) (getPatts b) PAlt a b -> liftM2 (++) (getPatts a) (getPatts b)
PString s -> return [K s] PString s -> return [K s]
PSeq a b -> do PSeq _ _ a _ _ b -> do
as <- getPatts a as <- getPatts a
bs <- getPatts b bs <- getPatts b
return [K (s ++ t) | K s <- as, K t <- bs] return [K (s ++ t) | K s <- as, K t <- bs]

2
src/compiler/GF/Compile/GrammarToCanonical.hs
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@@ -247,7 +247,7 @@ convert' gr vs = ppT
pat (PString s) = [s] pat (PString s) = [s]
pat (PAlt p1 p2) = pat p1++pat p2 pat (PAlt p1 p2) = pat p1++pat p2
pat (PSeq p1 p2) = [s1++s2 | s1<-pat p1, s2<-pat p2] pat (PSeq _ _ p1 _ _ p2) = [s1++s2 | s1<-pat p1, s2<-pat p2]
pat p = error $ "convert' alts pat: "++show p pat p = error $ "convert' alts pat: "++show p
fields = map field . filter (not.isLockLabel.fst) fields = map field . filter (not.isLockLabel.fst)

4
src/compiler/GF/Compile/Rename.hs
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@@ -306,10 +306,10 @@ renamePattern env patt =
(q',ws) <- renp q (q',ws) <- renp q
return (PAlt p' q', vs ++ ws) return (PAlt p' q', vs ++ ws)
PSeq p q -> do PSeq minp maxp p minq maxq q -> do
(p',vs) <- renp p (p',vs) <- renp p
(q',ws) <- renp q (q',ws) <- renp q
return (PSeq p' q', vs ++ ws) return (PSeq minp maxp p' minq maxq q', vs ++ ws)
PRep p -> do PRep p -> do
(p',vs) <- renp p (p',vs) <- renp p

39
src/compiler/GF/Compile/TypeCheck/Concrete.hs
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@@ -13,6 +13,7 @@ import GF.Grammar.Lockfield (isLockLabel, lockRecType, unlockRecord)
import GF.Compile.TypeCheck.Primitives import GF.Compile.TypeCheck.Primitives
import Data.List import Data.List
import Data.Maybe(fromMaybe)
import Control.Monad import Control.Monad
import GF.Text.Pretty import GF.Text.Pretty
@@ -290,7 +291,7 @@ inferLType gr g trm = case trm of
inferCase mty (patt,term) = do inferCase mty (patt,term) = do
arg <- maybe (inferPatt patt) return mty arg <- maybe (inferPatt patt) return mty
cont <- pattContext gr g arg patt cont <- pattContext gr g arg patt
(_,val) <- inferLType gr (reverse cont ++ g) term (term',val) <- inferLType gr (reverse cont ++ g) term
return (arg,val) return (arg,val)
isConstPatt p = case p of isConstPatt p = case p of
PC _ ps -> True --- all isConstPatt ps PC _ ps -> True --- all isConstPatt ps
@@ -302,7 +303,7 @@ inferLType gr g trm = case trm of
PFloat _ -> True PFloat _ -> True
PChar -> True PChar -> True
PChars _ -> True PChars _ -> True
PSeq p q -> isConstPatt p && isConstPatt q PSeq _ _ p _ _ q -> isConstPatt p && isConstPatt q
PAlt p q -> isConstPatt p && isConstPatt q PAlt p q -> isConstPatt p && isConstPatt q
PRep p -> isConstPatt p PRep p -> isConstPatt p
PNeg p -> isConstPatt p PNeg p -> isConstPatt p
@@ -314,12 +315,39 @@ inferLType gr g trm = case trm of
PAs _ p -> inferPatt p PAs _ p -> inferPatt p
PNeg p -> inferPatt p PNeg p -> inferPatt p
PAlt p q -> checks [inferPatt p, inferPatt q] PAlt p q -> checks [inferPatt p, inferPatt q]
PSeq _ _ -> return $ typeStr PSeq _ _ _ _ _ _ -> return $ typeStr
PRep _ -> return $ typeStr PRep _ -> return $ typeStr
PChar -> return $ typeStr PChar -> return $ typeStr
PChars _ -> return $ typeStr PChars _ -> return $ typeStr
_ -> inferLType gr g (patt2term p) >>= return . snd _ -> inferLType gr g (patt2term p) >>= return . snd
measurePatt p =
case p of
PR ass -> let p' = PR (map (\(lbl,p) -> let (_,_,p') = measurePatt p in (lbl,p')) ass)
in (0,Nothing,p')
PString s -> let len=length s
in (len,Just len,p)
PT t p -> let (min,max,p') = measurePatt p
in (min,max,PT t p')
PAs x p -> let (min,max,p') = measurePatt p
in (min,max,PAs x p')
PImplArg p -> let (min,max,p') = measurePatt p
in (min,max,PImplArg p')
PNeg p -> let (_,_,p') = measurePatt p
in (0,Nothing,PNeg p')
PAlt p1 p2 -> let (min1,max1,p1') = measurePatt p1
(min2,max2,p2') = measurePatt p2
in (min min1 min2,liftM2 max max1 max2,PAlt p1' p2')
PSeq _ _ p1 _ _ p2
-> let (min1,max1,p1') = measurePatt p1
(min2,max2,p2') = measurePatt p2
in (min1+min2,liftM2 (+) max1 max2,PSeq min1 (fromMaybe maxBound max1) p1' min2 (fromMaybe maxBound max2) p2')
PRep p -> let (_,_,p') = measurePatt p
in (0,Nothing,PRep p')
PChar -> (1,Just 1,p)
PChars _ -> (1,Just 1,p)
_ -> (0,Nothing,p)
-- type inference: Nothing, type checking: Just t -- type inference: Nothing, type checking: Just t
-- the latter permits matching with value type -- the latter permits matching with value type
getOverload :: SourceGrammar -> Context -> Maybe Type -> Term -> Check (Maybe (Term,Type)) getOverload :: SourceGrammar -> Context -> Maybe Type -> Term -> Check (Maybe (Term,Type))
@@ -596,7 +624,8 @@ checkLType gr g trm typ0 = do
checkCase arg val (p,t) = do checkCase arg val (p,t) = do
cont <- pattContext gr g arg p cont <- pattContext gr g arg p
t' <- justCheck (reverse cont ++ g) t val t' <- justCheck (reverse cont ++ g) t val
return (p,t') let (_,_,p') = measurePatt p
return (p',t')
pattContext :: SourceGrammar -> Context -> Type -> Patt -> Check Context pattContext :: SourceGrammar -> Context -> Type -> Patt -> Check Context
pattContext env g typ p = case p of pattContext env g typ p = case p of
@@ -633,7 +662,7 @@ pattContext env g typ p = case p of
fsep pts <+> fsep pts <+>
"in pattern alterantives" <+> ppPatt Unqualified 0 p) (null pts) "in pattern alterantives" <+> ppPatt Unqualified 0 p) (null pts)
return g1 -- must be g1 == g2 return g1 -- must be g1 == g2
PSeq p q -> do PSeq _ _ p _ _ q -> do
g1 <- pattContext env g typ p g1 <- pattContext env g typ p
g2 <- pattContext env g typ q g2 <- pattContext env g typ q
return $ g1 ++ g2 return $ g1 ++ g2

2
src/compiler/GF/Compile/TypeCheck/ConcreteNew.hs
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@@ -318,7 +318,7 @@ tcPatt ge scope (PString s) ty0 = do
tcPatt ge scope PChar ty0 = do tcPatt ge scope PChar ty0 = do
unify ge scope ty0 vtypeStr unify ge scope ty0 vtypeStr
return scope return scope
tcPatt ge scope (PSeq p1 p2) ty0 = do tcPatt ge scope (PSeq _ _ p1 _ _ p2) ty0 = do
unify ge scope ty0 vtypeStr unify ge scope ty0 vtypeStr
scope <- tcPatt ge scope p1 vtypeStr scope <- tcPatt ge scope p1 vtypeStr
scope <- tcPatt ge scope p2 vtypeStr scope <- tcPatt ge scope p2 vtypeStr

4
src/compiler/GF/Grammar/Binary.hs
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@@ -244,7 +244,7 @@ instance Binary Patt where
put (PAs x y) = putWord8 10 >> put (x,y) put (PAs x y) = putWord8 10 >> put (x,y)
put (PNeg x) = putWord8 11 >> put x put (PNeg x) = putWord8 11 >> put x
put (PAlt x y) = putWord8 12 >> put (x,y) put (PAlt x y) = putWord8 12 >> put (x,y)
put (PSeq x y) = putWord8 13 >> put (x,y) put (PSeq minx maxx x miny maxy y) = putWord8 13 >> put (minx,maxx,x,miny,maxy,y)
put (PRep x) = putWord8 14 >> put x put (PRep x) = putWord8 14 >> put x
put (PChar) = putWord8 15 put (PChar) = putWord8 15
put (PChars x) = putWord8 16 >> put x put (PChars x) = putWord8 16 >> put x
@@ -266,7 +266,7 @@ instance Binary Patt where
10 -> get >>= \(x,y) -> return (PAs x y) 10 -> get >>= \(x,y) -> return (PAs x y)
11 -> get >>= \x -> return (PNeg x) 11 -> get >>= \x -> return (PNeg x)
12 -> get >>= \(x,y) -> return (PAlt x y) 12 -> get >>= \(x,y) -> return (PAlt x y)
13 -> get >>= \(x,y) -> return (PSeq x y) 13 -> get >>= \(minx,maxx,x,miny,maxy,y) -> return (PSeq minx maxx x miny maxy y)
14 -> get >>= \x -> return (PRep x) 14 -> get >>= \x -> return (PRep x)
15 -> return (PChar) 15 -> return (PChar)
16 -> get >>= \x -> return (PChars x) 16 -> get >>= \x -> return (PChars x)

6
src/compiler/GF/Grammar/Grammar.hs
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@@ -421,8 +421,7 @@ data Patt =
-- regular expression patterns -- regular expression patterns
| PNeg Patt -- ^ negated pattern: -p | PNeg Patt -- ^ negated pattern: -p
| PAlt Patt Patt -- ^ disjunctive pattern: p1 | p2 | PAlt Patt Patt -- ^ disjunctive pattern: p1 | p2
| PSeq Patt Patt -- ^ sequence of token parts: p + q | PSeq Int Int Patt Int Int Patt -- ^ sequence of token parts: p + q
| PMSeq MPatt MPatt -- ^ sequence of token parts: p + q
| PRep Patt -- ^ repetition of token part: p* | PRep Patt -- ^ repetition of token part: p*
| PChar -- ^ string of length one: ? | PChar -- ^ string of length one: ?
| PChars [Char] -- ^ character list: ["aeiou"] | PChars [Char] -- ^ character list: ["aeiou"]
@@ -430,9 +429,6 @@ data Patt =
| PM QIdent -- #m.p | PM QIdent -- #m.p
deriving (Show, Eq, Ord) deriving (Show, Eq, Ord)
-- | Measured pattern (paired with the min & max matching length)
type MPatt = ((Int,Int),Patt)
-- | to guide computation and type checking of tables -- | to guide computation and type checking of tables
data TInfo = data TInfo =
TRaw -- ^ received from parser; can be anything TRaw -- ^ received from parser; can be anything

10
src/compiler/GF/Grammar/Macros.hs
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@@ -392,7 +392,7 @@ term2patt trm = case termForm trm of
Ok ([], Cn id, [a,b]) | id == cSeq -> do Ok ([], Cn id, [a,b]) | id == cSeq -> do
a' <- term2patt a a' <- term2patt a
b' <- term2patt b b' <- term2patt b
return (PSeq a' b') return (PSeq 0 maxBound a' 0 maxBound b')
Ok ([], Cn id, [a,b]) | id == cAlt -> do Ok ([], Cn id, [a,b]) | id == cAlt -> do
a' <- term2patt a a' <- term2patt a
b' <- term2patt b b' <- term2patt b
@@ -422,7 +422,7 @@ patt2term pt = case pt of
PAs x p -> appCons cAs [Vr x, patt2term p] --- an encoding PAs x p -> appCons cAs [Vr x, patt2term p] --- an encoding
PChar -> appCons cChar [] --- an encoding PChar -> appCons cChar [] --- an encoding
PChars s -> appCons cChars [K s] --- an encoding PChars s -> appCons cChars [K s] --- an encoding
PSeq a b -> appCons cSeq [(patt2term a), (patt2term b)] --- an encoding PSeq _ _ a _ _ b -> appCons cSeq [(patt2term a), (patt2term b)] --- an encoding
PAlt a b -> appCons cAlt [(patt2term a), (patt2term b)] --- an encoding PAlt a b -> appCons cAlt [(patt2term a), (patt2term b)] --- an encoding
PRep a -> appCons cRep [(patt2term a)] --- an encoding PRep a -> appCons cRep [(patt2term a)] --- an encoding
PNeg a -> appCons cNeg [(patt2term a)] --- an encoding PNeg a -> appCons cNeg [(patt2term a)] --- an encoding
@@ -475,8 +475,7 @@ composPattOp op patt =
PImplArg p -> liftM PImplArg (op p) PImplArg p -> liftM PImplArg (op p)
PNeg p -> liftM PNeg (op p) PNeg p -> liftM PNeg (op p)
PAlt p1 p2 -> liftM2 PAlt (op p1) (op p2) PAlt p1 p2 -> liftM2 PAlt (op p1) (op p2)
PSeq p1 p2 -> liftM2 PSeq (op p1) (op p2) PSeq _ _ p1 _ _ p2 -> liftM2 (\p1 p2 -> PSeq 0 maxBound p1 0 maxBound p2) (op p1) (op p2)
PMSeq (_,p1) (_,p2) -> liftM2 PSeq (op p1) (op p2) -- information loss
PRep p -> liftM PRep (op p) PRep p -> liftM PRep (op p)
_ -> return patt -- covers cases without subpatterns _ -> return patt -- covers cases without subpatterns
@@ -514,8 +513,7 @@ collectPattOp op patt =
PImplArg p -> op p PImplArg p -> op p
PNeg p -> op p PNeg p -> op p
PAlt p1 p2 -> op p1++op p2 PAlt p1 p2 -> op p1++op p2
PSeq p1 p2 -> op p1++op p2 PSeq _ _ p1 _ _ p2 -> op p1++op p2
PMSeq (_,p1) (_,p2) -> op p1++op p2
PRep p -> op p PRep p -> op p
_ -> [] -- covers cases without subpatterns _ -> [] -- covers cases without subpatterns

2
src/compiler/GF/Grammar/Parser.y
View File

@@ -485,7 +485,7 @@ Exps
Patt :: { Patt } Patt :: { Patt }
Patt Patt
: Patt '|' Patt1 { PAlt $1 $3 } : Patt '|' Patt1 { PAlt $1 $3 }
| Patt '+' Patt1 { PSeq $1 $3 } | Patt '+' Patt1 { PSeq 0 maxBound $1 0 maxBound $3 }
| Patt1 { $1 } | Patt1 { $1 }
Patt1 :: { Patt } Patt1 :: { Patt }

46
src/compiler/GF/Grammar/PatternMatch.hs
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@@ -15,8 +15,7 @@
module GF.Grammar.PatternMatch ( module GF.Grammar.PatternMatch (
matchPattern, matchPattern,
testOvershadow, testOvershadow,
findMatch, findMatch
measurePatt
) where ) where
import GF.Data.Operations import GF.Data.Operations
@@ -122,11 +121,10 @@ tryMatch (p,t) = do
Bad _ -> return [] Bad _ -> return []
_ -> raise (render ("no match with negative pattern" <+> p)) _ -> raise (render ("no match with negative pattern" <+> p))
(PSeq p1 p2, ([],K s, [])) -> matchPSeq p1 p2 s (PSeq min1 max1 p1 min2 max2 p2, ([],K s, [])) -> matchPSeq min1 max1 p1 min2 max2 p2 s
(PMSeq mp1 mp2, ([],K s, [])) -> matchPMSeq mp1 mp2 s
(PRep p1, ([],K s, [])) -> checks [ (PRep p1, ([],K s, [])) -> checks [
trym (foldr (const (PSeq p1)) (PString "") trym (foldr (const (PSeq 0 maxBound p1 0 maxBound)) (PString "")
[1..n]) t' | n <- [0 .. length s] [1..n]) t' | n <- [0 .. length s]
] >> ] >>
return [] return []
@@ -140,12 +138,7 @@ tryMatch (p,t) = do
words2term [w] = K w words2term [w] = K w
words2term (w:ws) = C (K w) (words2term ws) words2term (w:ws) = C (K w) (words2term ws)
matchPSeq min1 max1 p1 min2 max2 p2 s =
matchPMSeq (m1,p1) (m2,p2) s = matchPSeq' m1 p1 m2 p2 s
--matchPSeq p1 p2 s = matchPSeq' (0,maxBound::Int) p1 (0,maxBound::Int) p2 s
matchPSeq p1 p2 s = matchPSeq' (lengthBounds p1) p1 (lengthBounds p2) p2 s
matchPSeq' b1@(min1,max1) p1 b2@(min2,max2) p2 s =
do let n = length s do let n = length s
lo = min1 `max` (n-max2) lo = min1 `max` (n-max2)
hi = (n-min2) `min` max1 hi = (n-min2) `min` max1
@@ -153,37 +146,6 @@ matchPSeq' b1@(min1,max1) p1 b2@(min2,max2) p2 s =
matches <- checks [mapM tryMatch [(p1,K s1),(p2,K s2)] | (s1,s2) <- cuts] matches <- checks [mapM tryMatch [(p1,K s1),(p2,K s2)] | (s1,s2) <- cuts]
return (concat matches) return (concat matches)
-- | Estimate the minimal length of the string that a pattern will match
minLength = matchLength 0 id (+) min -- safe underestimate
-- | Estimate the maximal length of the string that a pattern will match
maxLength =
maybe maxBound id . matchLength Nothing Just (liftM2 (+)) (liftM2 max)
-- safe overestimate
matchLength unknown known seq alt = len
where
len p =
case p of
PString s -> known (length s)
PSeq p1 p2 -> seq (len p1) (len p2)
PAlt p1 p2 -> alt (len p1) (len p2)
PChar -> known 1
PChars _ -> known 1
PAs x p' -> len p'
PT t p' -> len p'
_ -> unknown
lengthBounds p = (minLength p,maxLength p)
mPatt p = (lengthBounds p,measurePatt p)
measurePatt p =
case p of
PSeq p1 p2 -> PMSeq (mPatt p1) (mPatt p2)
_ -> composSafePattOp measurePatt p
isInConstantForm :: Term -> Bool isInConstantForm :: Term -> Bool
isInConstantForm trm = case trm of isInConstantForm trm = case trm of
Cn _ -> True Cn _ -> True

3
src/compiler/GF/Grammar/Printer.hs
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@@ -250,8 +250,7 @@ ppCase q (p,e) = ppPatt q 0 p <+> "=>" <+> ppTerm q 0 e
instance Pretty Patt where pp = ppPatt Unqualified 0 instance Pretty Patt where pp = ppPatt Unqualified 0
ppPatt q d (PAlt p1 p2) = prec d 0 (ppPatt q 0 p1 <+> '|' <+> ppPatt q 1 p2) ppPatt q d (PAlt p1 p2) = prec d 0 (ppPatt q 0 p1 <+> '|' <+> ppPatt q 1 p2)
ppPatt q d (PSeq p1 p2) = prec d 0 (ppPatt q 0 p1 <+> '+' <+> ppPatt q 1 p2) ppPatt q d (PSeq _ _ p1 _ _ p2) = prec d 0 (ppPatt q 0 p1 <+> '+' <+> ppPatt q 1 p2)
ppPatt q d (PMSeq (_,p1) (_,p2)) = prec d 0 (ppPatt q 0 p1 <+> '+' <+> ppPatt q 1 p2)
ppPatt q d (PC f ps) = if null ps ppPatt q d (PC f ps) = if null ps
then pp f then pp f
else prec d 1 (f <+> hsep (map (ppPatt q 3) ps)) else prec d 1 (f <+> hsep (map (ppPatt q 3) ps))