(define (generate-double-tag-function tag-name)
  (lambda (contents . attributes)
    (double-tag tag-name contents attributes)))

(define (generate-single-tag-function tag-name)
  (lambda attributes
    (single-tag tag-name attributes)))

(define (single-tag name attributes)
 (start-tag name attributes))

(define (double-tag name contents attributes)
 (string-append (start-tag name attributes)
                (as-string contents)
                (end-tag name)))



(define (start-tag kind attributes)
  (if (null? attributes) 
      (string-append "<" kind ">")
      (let ((html-attributes (linearize-attributes attributes)))
         (string-append "<" kind " " html-attributes " >"))))

(define (end-tag kind)
  (string-append "</" kind ">"))

(define (linearize-attributes attr-list)
  (string-append  
    (linearize-attributes-1
      (reverse attr-list) "" (length attr-list))))

(define (linearize-attributes-1 attr-list res-string lgt)
  (cond ((null? attr-list) res-string)
        ((>= lgt 2) 
          (linearize-attributes-1 
           (cddr attr-list)
           (string-append 
            (linearize-attribute-pair
             (car attr-list) (cadr attr-list)) " " res-string)
           (- lgt 2)))
        ((< lgt 2) 
          (error "The attribute list must have even length"))))

(define (linearize-attribute-pair val attr)
  (string-append (as-string attr)
                  " = " (string-it (as-string val))))

(define (map-concat f lst)
  (apply string-append (map f lst)))