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module GF.Command.TreeOperations (
treeOp,
allTreeOps
) where
import PGF
import PGF.Data
import Data.List
type TreeOp = [Expr] -> [Expr]
treeOp :: PGF -> String -> Maybe (Either TreeOp (CId -> TreeOp))
treeOp pgf f = fmap snd $ lookup f $ allTreeOps pgf
allTreeOps :: PGF -> [(String,(String,Either TreeOp (CId -> TreeOp)))]
allTreeOps pgf = [
("compute",("compute by using semantic definitions (def)",
Left $ map (compute pgf))),
("transfer",("syntactic transfer by applying function, recursively in subtrees",
Right $ \f -> map (transfer pgf f))),
("paraphrase",("paraphrase by using semantic definitions (def)",
Left $ nub . concatMap (paraphrase pgf))),
("largest",("sort trees from largest to smallest, in number of nodes",
Left $ largest)),
("nub",("remove duplicate trees",
Left $ nub)),
("smallest",("sort trees from smallest to largest, in number of nodes",
Left $ smallest)),
("subtrees",("return all fully applied subtrees (stopping at abstractions), by default sorted from the largest",
Left $ concatMap subtrees))
]
largest :: [Expr] -> [Expr]
largest = reverse . smallest
smallest :: [Expr] -> [Expr]
smallest = sortBy (\t u -> compare (size t) (size u)) where
size t = case t of
EAbs _ _ e -> size e + 1
EApp e1 e2 -> size e1 + size e2 + 1
_ -> 1
subtrees :: Expr -> [Expr]
subtrees t = t : case unApp t of
Just (f,ts) -> concatMap subtrees ts
_ -> [] -- don't go under abstractions
--- simple-minded transfer; should use PGF.Expr.match
transfer :: PGF -> CId -> Expr -> Expr
transfer pgf f e = case transf e of
v | v /= appf e -> v
_ -> case e of
EApp g a -> EApp (transfer pgf f g) (transfer pgf f a)
_ -> e
where
appf = EApp (EFun f)
transf = compute pgf . appf
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