extensible options-spec for getopt-long

(use-modules
  (ice-9 getopt-long))

(define supported-props
  (alist->hash-table
   (map
    (lambda (k)
      (cons k #t))
    '(single-char value required? predicate))))

(define (conform-props props)
  (fold-right
   (lambda (kv new-props)
     (if (hash-ref supported-props (car kv))
     (cons kv new-props)
     new-props))
   #nil
   props))

(define (conform-spec spec)
  (map
   (lambda (kv)
     (cons
      (car kv)
      (conform-props (cdr kv))))
   spec))

(define (getopt-long args options-spec)
  ((@ (ice-9 getopt-long) getopt-long)
   args (conform-spec options-spec)))