HXQ-0.7: XQueryInterpreter.hs
{-------------------------------------------------------------------------------------
-
- The XQuery Interpreter
- Programmer: Leonidas Fegaras
- Email: fegaras@cse.uta.edu
- Web: http://lambda.uta.edu/
- Creation: 03/22/08, last update: 04/10/08
-
- Copyright (c) 2008 by Leonidas Fegaras, the University of Texas at Arlington. All rights reserved.
- This material is provided as is, with absolutely no warranty expressed or implied.
- Any use is at your own risk. Permission is hereby granted to use or copy this program
- for any purpose, provided the above notices are retained on all copies.
-
--------------------------------------------------------------------------------------}
{-# OPTIONS_GHC -fth #-}
module XQueryInterpreter where
import List(sortBy)
import XMLParse(parseDocument)
import XQueryParser
import XQueryCompiler
-- system functions (=, concat, etc)
systemFunctions :: [(String,Int,[XSeq]->XSeq)]
systemFunctions = $(iFunctions)
-- XPath step functions (child, descendant, etc)
pathFunctions :: [(String,Tag->XTree->XSeq)]
pathFunctions = $(pFunctions)
-- run-time bindings of FLOWR variables
type Environment = [(String,XSeq)]
-- a user-defined function is (fname,parameters,body)
type Functions = [(String,[String],Ast)]
undefv1 = error "Undefined XQuery context (.)"
undefv2 = error "Undefined position()"
undefv3 = error "Undefined last()"
-- Each XPath predicate must calculate position() and last() from its input XSeq
-- if last() is used, then the evaluation is blocking (need to store the whole input XSeq)
applyPredicates :: [Ast] -> XSeq -> Environment -> Functions -> XSeq
applyPredicates [] xs _ _ = xs
applyPredicates (pred:preds) xs env fncs
| containsLast pred -- blocking: use only when last() is used in the predicate
= let last = length xs
in applyPredicates preds
(foldir (\x i r -> if case eval pred x i last "" env fncs of
[XInt k] -> k == i -- indexing
b -> conditionTest b
then x:r else r) [] xs 1) env fncs
applyPredicates (pred:preds) xs env fncs
= applyPredicates preds
(foldir (\x i r -> if case eval pred x i undefv3 "" env fncs of
[XInt k] -> k == i -- indexing
b -> conditionTest b
then x:r else r) [] xs 1) env fncs
-- The XQuery interpreter
-- context: context node (XPath .)
-- position: the element position in the parent sequence (XPath position())
-- last: the length of the parent sequence (XPath last())
-- effective_axis: the XPath axis in /axis::tag(exp)
-- (eg, the effective axis of //(A | B) is "descendant_step"
-- env: contains FLOWR variable bindings
-- fncs: user-defined functions
eval :: Ast -> XTree -> Int -> Int -> String -> Environment -> Functions -> XSeq
eval e context position last effective_axis env fncs
= case e of
Avar "." -> [ context ]
Avar v -> findV v env
Aint n -> [ XInt n ]
Afloat n -> [ XFloat n ]
Astring s -> [ XText s ]
Ast "doc" [Aint n] -> findV ("_doc"++(show n)) env
Ast "context" [v,Astring dp,body]
-> foldr (\x r -> (eval body x position last dp env fncs)++r)
[] (eval v context position last effective_axis env fncs)
Ast "call" [Avar "position"] -> [XInt position]
Ast "call" [Avar "last"] -> [XInt last]
Ast "step" [Ast "child_step" [tag, Avar "."]]
| effective_axis /= ""
-> eval (Ast "step" [Ast effective_axis [tag, Avar "."]]) context position last "" env fncs
Ast "step" [Ast path_step [Astring tag,body]]
| memV path_step pathFunctions
-> foldr (\x r -> ((findV path_step pathFunctions) tag x)++r)
[] (eval body context position last effective_axis env fncs)
Ast "step" ((Ast path_step [Astring tag,body]):predicates)
| memV path_step pathFunctions
-> foldr (\x r -> (applyPredicates predicates ((findV path_step pathFunctions) tag x) env fncs)++r)
[] (eval body context position last effective_axis env fncs)
Ast "step" [exp]
-> eval exp context position last effective_axis env fncs
Ast "step" (exp:predicates)
-> applyPredicates predicates (eval exp context position last effective_axis env fncs) env fncs
Ast "predicate" [condition,body]
-> applyPredicates [condition] (eval body context position last effective_axis env fncs) env fncs
Ast "call" ((Avar fname):args)
-> case filter (\(n,_,_) -> n == fname || ("fn:"++n) == fname) systemFunctions of
[(_,len,f)] -> if (length args) == len
then f (map (\x -> eval x context position last effective_axis env fncs) args)
else error ("Wrong number of arguments in system call: "++fname)
_ -> case filter (\(n,_,_) -> n == fname) fncs of
[(_,params,body)] -> if (length params) == (length args)
then eval body context undefv2 undefv3 ""
((zipWith (\p a -> (p,eval a context position last effective_axis env fncs))
params args)++env) fncs
else error ("Wrong number of arguments in function call: "++fname)
_ -> error ("Undefined function: "++fname)
Ast "construction" [Astring tag,Ast "attributes" [],body]
-> [ XElem tag [] 0 (eval body context position last effective_axis env fncs) ]
Ast "construction" [tag,Ast "attributes" al,body]
-> let alc = map (\(Ast "pair" [a,v])
-> let ac = eval a context position last effective_axis env fncs
vc = eval v context position last effective_axis env fncs
in (qName ac,showXS (text vc))) al
ct = eval tag context position last effective_axis env fncs
bc = eval body context position last effective_axis env fncs
in [ XElem (qName ct) alc 0 bc ]
Ast "let" [Avar var,source,body]
-> eval body context position last effective_axis ((var,eval source context position last effective_axis env fncs):env) fncs
Ast "for" [Avar var,Avar "$",source,body] -- a for-loop without an index
-> foldr (\a r -> (eval body a undefv2 undefv3 "" ((var,[a]):env) fncs)++r)
[] (eval source context position last effective_axis env fncs)
Ast "for" [Avar var,Avar ivar,source,body] -- a for-loop with an index
-> foldir (\a i r -> (eval body a i undefv3 "" ((var,[a]):(ivar,[XInt i]):env) fncs)++r)
[] (eval source context position last effective_axis env fncs) 1
Ast "sortTuple" (exp:orderBys) -- prepare each FLWOR tuple for sorting
-> [ XElem "" [] 0 (foldl (\r a -> r++[XElem "" [] 0 (text (eval a context position last effective_axis env fncs))])
[XElem "" [] 0 (eval exp context position last effective_axis env fncs)] orderBys) ]
Ast "sort" (exp:ordList)
-> let ce = map (\(XElem _ _ _ xs) -> map (\(XElem _ _ _ ys) -> ys) xs)
(eval exp context position last effective_axis env fncs)
ordering = foldr (\(Avar ord) r (x:xs) (y:ys)
-> case compareXSeqs (ord == "ascending") x y of
EQ -> r xs ys
o -> o)
(\xs ys -> EQ) ordList
in concatMap head (sortBy (\(_:xs) (_:ys) -> ordering xs ys) ce)
_ -> error ("Illegal XQuery: "++(show e))
-- the XQuery interpreter
xquery :: String -> IO XSeq
xquery query
= do let asts = parse (scan query)
fncs = foldr (\e r -> case e of
Ast "function" ((Avar f):b:args) -> (f,map (\(Avar v) -> v) args,optimize b):r
_ -> r) [] asts
vars = foldl (\r e -> case e of
Ast "variable" [Avar v,u] -> (v,eval (optimize u) undefv1 undefv2 undefv3 "" r fncs):r
_ -> r) [] asts
(ast,_,ns) = getDocs (last asts) 0
env <- foldr (\(n,s) r -> case s of
Astring file -> do doc <- readFile file
env <- r
return (("_doc"++(show n),[materialize (parseDocument doc)]):env)
Aint m -> do env <- r
return (("_doc"++(show n),findV ("_doc"++(show m)) env):env))
(return []) ns
return (eval (optimize ast) undefv1 undefv2 undefv3 "" (env++vars) fncs)
-- Read an XQuery fom a file and run it
xfile :: String -> IO XSeq
xfile file = do query <- readFile file
xquery query