;;; PLT Scheme Inference Collection
;;; facts.ss
;;; Copyright (c) 2006 M. Douglas Williams
;;;
;;; This library is free software; you can redistribute it and/or
;;; modify it under the terms of the GNU Lesser General Public
;;; License as published by the Free Software Foundation; either
;;; version 2.1 of the License, or (at your option) any later version.
;;;
;;; This library is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;; Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this library; if not, write to the Free
;;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
;;; 02111-1307 USA.
;;;

(module facts mzscheme
  
  (provide (all-defined))
  
  ;; fact?: any -> boolean
  (define (fact? x)
    (or (and (pair? x)
             (symbol? (car x)))
        (and (vector? x)
             (> (vector-length x) 0)
             (symbol? (vector-ref x 0)))))
  
  ;; fact-first: fact? -> symbol
  (define (fact-first fact)
    (cond ((pair? fact)
           (car fact))
          ((vector? fact)
           (vector-ref fact 0))
          ((struct? fact)
           (vector-ref (struct->vector fact) 0))))
  
  )