Hello list I'm trying to use racket's implementation of datalog as a query language for a small database (5 gb). I'm running into some problems that I'd appreciate your help with:
* Is there support for negating a subgoal? E.g: [1]
Get the names of employees who do not work on any project.
temp1(S) :- works_on(S,_,_).
answer(F,M,L) :- employee(F,M,L,S,_,_,_,_,_,_), not temp1(S).
* Is there support for other comparison operators outside {=, !=}? E.g.
(datalog *db*
;; shareholders
(! (shareholder "Jorge" person))
(! (shareholder "Bob" person))
(! (shareholder "Googly" company))
(! (shareholder "Megasoft" company))
;; ownership
(! (owns-a-share "Jorge" "Construction SA" 60.8))
(! (owns-a-share "Bob" "Construction SA" 39.2))
(! (owns-a-share "Bob" "WAKA SA" 100 ))
(! (owns-a-share "Googly" "Toys SA" 100 )))
(let ((majority? (λ (percent)
(> percent 50))))
(datalog *db*
(! (:- (major-stockholder COMPANY)
(shareholder SHAREHOLDER person)
(owns-a-share SHAREHOLDER COMPANY PERCENT)
(majority? PERCENT :- TEMP)
(= TEMP true)))))
* A syntax extension difficulty, not very much related to datalog per
se. I have this syntax extension:
(define-syntax (->relations stx)
;; point here being getting true relations (sets) out of the results
(syntax-case stx ()
[(_ rel-name rel-size)
(with-syntax ([rel-vars (for/list ([x (in-range (syntax->datum
#'rel-size))])
(gensym 'X))])
#`(map (λ (dic)
(list->set
(map (λ (rel-var)
(hash-ref dic rel-var))
#'rel-vars)))
(datalog *db* (? (#,#'rel-name
#,@#'rel-vars)))))]))
This is an case of an usage, in the context of the previous example:
(->relations major-stockholder 1)
I'm bumping in the following error:
make-variable: contract violation
expected: (or/c #f (list/c any/c (or/c exact-positive-integer? #f) (or/c
exact-nonnegative-integer? #f) (or/c exact-nonnegative-integer? #f) (or/c
exact-positive-integer? #f)))
given: '(#f #f #f #f 0)
in: the 1st argument of
(->
(or/c
#f
(list/c
any/c
(or/c exact-positive-integer? #f)
(or/c exact-nonnegative-integer? #f)
(or/c exact-nonnegative-integer? #f)
(or/c exact-positive-integer? #f)))
symbol?
variable?)
contract from: <pkgs>/datalog/ast.rkt
Which I interpreted as the LOC being lost in the syntax generator. I
haven't being able to resolve that yet. Any light on the subject?
Thanks in advance for any pointers.
[1] http://tinman.cs.gsu.edu/~raj/8710/f05/datalog.pdf
--
Eduardo Bellani
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