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;;; srfi-11.scm --- let-values and let*-values
;; Copyright (C) 2000, 2001, 2002, 2004, 2006, 2009 Free Software Foundation, Inc.
;;
;; 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 3 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;; Commentary:
;; This module exports two syntax forms: let-values and let*-values.
;;
;; Sample usage:
;;
;; (let-values (((x y . z) (foo a b))
;; ((p q) (bar c)))
;; (baz x y z p q))
;;
;; This binds `x' and `y' to the first to values returned by `foo',
;; `z' to the rest of the values from `foo', and `p' and `q' to the
;; values returned by `bar'. All of these are available to `baz'.
;;
;; let*-values : let-values :: let* : let
;;
;; This module is fully documented in the Guile Reference Manual.
;;; Code:
(define-module (srfi srfi-11)
:export-syntax (let-values let*-values))
(cond-expand-provide (current-module) '(srfi-11))
;;;;;;;;;;;;;;
;; let-values
;;
;; Current approach is to translate
;;
;; (let-values (((x y . z) (foo a b))
;; ((p q) (bar c)))
;; (baz x y z p q))
;;
;; into
;;
;; (call-with-values (lambda () (foo a b))
;; (lambda (<tmp-x> <tmp-y> . <tmp-z>)
;; (call-with-values (lambda () (bar c))
;; (lambda (<tmp-p> <tmp-q>)
;; (let ((x <tmp-x>)
;; (y <tmp-y>)
;; (z <tmp-z>)
;; (p <tmp-p>)
;; (q <tmp-q>))
;; (baz x y z p q))))))
;; We could really use quasisyntax here...
(define-syntax let-values
(lambda (x)
(syntax-case x ()
((_ ((binds exp)) b0 b1 ...)
(syntax (call-with-values (lambda () exp)
(lambda binds b0 b1 ...))))
((_ (clause ...) b0 b1 ...)
(let lp ((clauses (syntax (clause ...)))
(ids '())
(tmps '()))
(if (null? clauses)
(with-syntax (((id ...) ids)
((tmp ...) tmps))
(syntax (let ((id tmp) ...)
b0 b1 ...)))
(syntax-case (car clauses) ()
(((var ...) exp)
(with-syntax (((new-tmp ...) (generate-temporaries
(syntax (var ...))))
((id ...) ids)
((tmp ...) tmps))
(with-syntax ((inner (lp (cdr clauses)
(syntax (var ... id ...))
(syntax (new-tmp ... tmp ...)))))
(syntax (call-with-values (lambda () exp)
(lambda (new-tmp ...) inner))))))
((vars exp)
(with-syntax ((((new-var . new-tmp) ...)
(let lp ((vars (syntax vars)))
(syntax-case vars ()
((id . rest)
(acons (syntax id)
(car
(generate-temporaries (syntax (id))))
(lp (syntax rest))))
(id (acons (syntax id)
(car
(generate-temporaries (syntax (id))))
'())))))
((id ...) ids)
((tmp ...) tmps))
(with-syntax ((inner (lp (cdr clauses)
(syntax (new-var ... id ...))
(syntax (new-tmp ... tmp ...))))
(args (let lp ((tmps (syntax (new-tmp ...))))
(syntax-case tmps ()
((id) (syntax id))
((id . rest) (cons (syntax id)
(lp (syntax rest))))))))
(syntax (call-with-values (lambda () exp)
(lambda args inner)))))))))))))
;;;;;;;;;;;;;;
;; let*-values
;;
;; Current approach is to translate
;;
;; (let*-values (((x y z) (foo a b))
;; ((p q) (bar c)))
;; (baz x y z p q))
;;
;; into
;;
;; (call-with-values (lambda () (foo a b))
;; (lambda (x y z)
;; (call-with-values (lambda (bar c))
;; (lambda (p q)
;; (baz x y z p q)))))
(define-syntax let*-values
(syntax-rules ()
((let*-values () body ...)
(let () body ...))
((let*-values ((vars-1 binding-1) (vars-2 binding-2) ...) body ...)
(call-with-values (lambda () binding-1)
(lambda vars-1
(let*-values ((vars-2 binding-2) ...)
body ...))))))
;;; srfi-11.scm ends here
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