ice-9/and-let-star.scm

   1 ;;;; and-let-star.scm --- and-let* syntactic form (draft SRFI-2) for Guile
   2 ;;;; written by Michael Livshin <mike@olan.com>
   3 ;;;;
   4 ;;;;    Copyright (C) 1999, 2001, 2004, 2006 Free Software Foundation, Inc.
   5 ;;;;
   6 ;;;; This library is free software; you can redistribute it and/or
   7 ;;;; modify it under the terms of the GNU Lesser General Public
   8 ;;;; License as published by the Free Software Foundation; either
   9 ;;;; version 2.1 of the License, or (at your option) any later version.
  10 ;;;;
  11 ;;;; This library is distributed in the hope that it will be useful,
  12 ;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 ;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 ;;;; Lesser General Public License for more details.
  15 ;;;;
  16 ;;;; You should have received a copy of the GNU Lesser General Public
  17 ;;;; License along with this library; if not, write to the Free Software
  18 ;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19
  20 (define-module (ice-9 and-let-star)
  21   :export-syntax (and-let*))
  22
  23 (defmacro and-let* (vars . body)
  24
  25   (define (expand vars body)
  26     (cond
  27      ((null? vars)
  28       (if (null? body)
  29           #t
  30           `(begin ,@body)))
  31      ((pair? vars)
  32       (let ((exp (car vars)))
  33         (cond
  34          ((pair? exp)
  35           (cond
  36            ((null? (cdr exp))
  37             `(and ,(car exp) ,(expand (cdr vars) body)))
  38            (else
  39             (let ((var (car exp)))
  40               `(let (,exp)
  41                  (and ,var ,(expand (cdr vars) body)))))))
  42          (else
  43           `(and ,exp ,(expand (cdr vars) body))))))
  44      (else
  45       (error "not a proper list" vars))))
  46
  47   (expand vars body))
  48
  49 (cond-expand-provide (current-module) '(srfi-2))