(use-modules (gnu packages)
             (guix packages)
             (guix sets)
             (ice-9 match)
             (ice-9 vlist)
             (srfi srfi-1))

(define all (all-packages))

(define (p->k p)
  (string-append (package-name p) "@" (package-version p)))

(define vall-packages
  (fold (lambda (package result)
          (vhash-cons (p->k package) package result))
        vlist-null
        all))

(define vleaf-packages
  (vhash-fold (lambda (key package result)
                (let loop ((dependencies (package-direct-inputs package))
                           (updated result))
                  (match dependencies
                    ('() updated)
                    ((or ((_ p) . tail)
                         ((_ p _) . tail))
                     (if (package? p)
                         (loop tail
                               (vhash-delete (p->k p) updated))
                         (loop tail updated))))))
              vall-packages
              vall-packages))

(define leaf-packages
  (vhash-fold (lambda (key package result)
                (cons package result))
              '()
              vleaf-packages))

(packages->manifest
 leaf-packages)