Hello,
I am trying to write a (simple) function to convert s-expressions to XML.
I've come up with following function, which (somehow) works:
(use-modules (ice-9 rdelim))
(use-modules (ice-9 pretty-print))
(define atom?
(lambda (x)
(and (not (pair? x)) (not (null? x)))))
(define (indent string count)
(if (< count 1)
""
(string-append string (indent string (- count 1)))))
(define (walklist expr level)
(if (null? expr)
'()
(begin
(sexp->xml (car expr) (+ level 1))
(walklist (cdr expr) level))))
(define (unknown->string expr)
(let ((s (open-output-string)))
(display expr s)
(get-output-string s)))
(define (sexp->xml expr . params)
(let ((level (if (null? params) 0 (car params))))
(cond
((atom? expr)
(simple-format #t "~A~A\n" (indent " " level) expr))
((list? (car expr))
(sexp->xml (car expr) (+ level 1))
(walklist (cdr expr) level))
; ((pair? expr)
; (simple-format #t "~A~A\n" (indent " " level) (car expr))
; (simple-format #t "~A~A\n" (indent " " level) (cdr expr)))
(#t
(let ((s (unknown->string (car expr))))
(simple-format #t "~A~A~A~A\n" (indent " " level) "<" s ">")
(walklist (cdr expr) level)
(simple-format #t "~A~A~A~A\n" (indent " " level) "</" s ">"))))))
(sexp->xml '(person
(name "myself")
(address
(street "somestreet" 2)
(town 1234 "thistown")
(country "wonderland")
(test 'a b)
; (test1 . asd)
(test2 '(asd "asd")))))
While this seems to work, it has some drawbacks, which I can not figure out
how to get rid of them:
- It doesn't work on pairs. When I uncomment the case which checks for pairs,
the result is no longer XML. Instead, it looks more like the output of
(display)
- There is no way to tell symbols from strings in the XML output.
- I'd like atoms to be enclosed into its tags without any whitespace. While
it is easy to get rid of the indentation and the trailing newline, I can't
figure out how to get rid of the newline that comes behind the opening tag
Any hints?
BTW: In addition, I'd appreciate any hints how to make this thing more
scheme'ish. I think there is lots of potential for improvement here.
