I am trying to add a matrix and it is not working...

(define (matrix-matrix-add a b)
  (map (lambda (row) (row-matrix-add row b))
       a))

(define (row-matrix-add row matrix)
  (if (null? (car matrix))
      '()
      (cons (add-m row (map car matrix))
            (row-matrix-add row (map cdr matrix)))))

(define (add-m row col)
  (if (null? col)
      0
      (+ (car row)
         (car col)
         (add-m (cdr row) (cdr col)))))