####List Query

A query language written in Scheme for querying lists (e.g. trees, SXML).

Only backend implemented so far.

######Similar to the Scheme "match" macro to perform queries on lists:

(define m 
  '(html (body
          (h1 "example")
          (a (@ (href "link1.com")) "link1 desc")
          (br)
          (a (@ (href "link2.com")) "link2 desc"))))
		  
(query-match m
  ((html (body (a (@ (href ,x)) ,y) ...))
   (list x y))
  (else #f))

=> '(("link1.com" "link1 desc") ("link2.com" "link2 desc"))

######Predicates:

(define m '((val 5) (val 120) (val 33) (val 3) (val 65)))

(query-match m
  (((val (? > ,x 20)) ...)
   x)
  (else #f))

=> '(120 33 65)

######Recursive search, like a normal search except when no match found, it will recursively run on the sublists:

(define m
  '(html (body
          (p (a (@ (href "q.com") "q")) (br) (a (@ (href "r.com") "r"))) 
          (div (a (@ (href "s.com") "s"))
               (a (@ (href "t.com") "t" (div (@ (name "aa") 111))))
               (div (@ (name "bb") 222))
               (div (@ (name "cc") 333 (div (@ (name "dd") 444))))
               (div (@ (name "ee") (p 5) (p 6)))))))

(query-match m
  ( (^(a (@ (href ,x))) ...
     ^(div (@ (name ,y) z ...)) ...)
   (list x y z) )
  (else #f))

=>

'( ("q.com" "r.com" "s.com" "t.com")
   ("aa" "bb" "cc" "ee") 
   ((111)
    (222)
    (333 (div (@ (name "dd") 444)))
    ((p 5) (p 6))) )

#####TODO:

• match macro for frontend
• look at using 'joins' (SQL like)
• look at using backtracking (PROLOG like)