Revert "SRFI-45: Support multiple values; add promise? predicate."

This reverts commit 1d64b4edb9.

doc/ref/srfi-modules.texi

@@ -3845,58 +3845,45 @@ words, no program that uses the R5RS definitions of delay and force will
 break if those definition are replaced by the SRFI-45 definitions of
 delay and force.
 
-Guile compatibly extends SRFI-45 to support multiple values.  It also
-adds @code{promise?} to the list of exports.
-
-@deffn {Scheme Procedure} promise? obj
-Return true if @var{obj} is an SRFI-45 promise, otherwise return false.
-@end deffn
-
 @deffn {Scheme Syntax} delay expression
-Takes an expression and returns a promise which at some point in the
+Takes an expression of arbitrary type @var{a} and returns a promise of
-future may be asked (by the @code{force} procedure) to evaluate the
+type @code{(Promise @var{a})} which at some point in the future may be
-expression and deliver the resulting value(s).
+asked (by the @code{force} procedure) to evaluate the expression and
+deliver the resulting value.
 @end deffn
 
 @deffn {Scheme Syntax} lazy expression
-Takes an expression (which must evaluate to a promise) and returns a
+Takes an expression of type @code{(Promise @var{a})} and returns a
-promise which at some point in the future may be asked (by the
+promise of type @code{(Promise @var{a})} which at some point in the
-@code{force} procedure) to evaluate the expression and deliver the
+future may be asked (by the @code{force} procedure) to evaluate the
-resulting promise.
+expression and deliver the resulting promise.
 @end deffn
 
-@deffn {Scheme Procedure} force promise
+@deffn {Scheme Procedure} force expression
-Takes a promise and returns the associated value(s) as follows: If
+Takes an argument of type @code{(Promise @var{a})} and returns a value
-value(s) have been computed for the promise, these value(s) are
+of type @var{a} as follows: If a value of type @var{a} has been computed
-returned.  Otherwise, the promise is first evaluated, then overwritten
+for the promise, this value is returned.  Otherwise, the promise is
-by the obtained promise or value(s), and then force is again applied
+first evaluated, then overwritten by the obtained promise or value, and
-(iteratively) to the promise.
+then force is again applied (iteratively) to the promise.
 @end deffn
 
-@deffn {Scheme Procedure} eager obj ...
+@deffn {Scheme Procedure} eager expression
-Takes any number of argument(s) and returns a promise.  As opposed to
+Takes an argument of type @var{a} and returns a value of type
-@code{delay}, the argument(s) are evaluated eagerly.  Semantically,
+@code{(Promise @var{a})}.  As opposed to @code{delay}, the argument is
-writing @code{(eager expression)} is equivalent to writing
+evaluated eagerly. Semantically, writing @code{(eager expression)} is
+equivalent to writing
 
 @lisp
 (let ((value expression)) (delay value)).
 @end lisp
 
 However, the former is more efficient since it does not require
-unnecessary creation and evaluation of thunks.  For expressions that
+unnecessary creation and evaluation of thunks. We also have the
-return a single value, we also have the equivalence
+equivalence
 
 @lisp
 (delay expression) = (lazy (eager expression))
 @end lisp
-
-More generally, the following equivalence holds:
-
-@lisp
-(delay expression) = (lazy (call-with-values
-                               (lambda () expression)
-                             eager))
-@end lisp
 @end deffn
 
 The following reduction rules may be helpful for reasoning about these
@@ -3906,7 +3893,7 @@ usage semantics specified above:
 @lisp
 (force (delay expression)) -> expression
 (force (lazy  expression)) -> (force expression)
-(force (eager obj ...))    -> (values obj ...)
+(force (eager value))      -> value
 @end lisp
 
 @subsubheading Correct usage

module/srfi/srfi-45.scm

@@ -1,6 +1,6 @@
 ;;; srfi-45.scm -- Primitives for Expressing Iterative Lazy Algorithms
 
-;; Copyright (C) 2010, 2011, 2013 Free Software Foundation, Inc.
+;; Copyright (C) 2010, 2011 Free Software Foundation, Inc.
 ;; Copyright (C) 2003 André van Tonder. All Rights Reserved.
 
 ;; Permission is hereby granted, free of charge, to any person
@@ -25,8 +25,8 @@
 
 ;;; Commentary:
 
-;; This is the code of the reference implementation of SRFI-45,
+;; This is the code of the reference implementation of SRFI-45, slightly
-;; modified to use SRFI-9 and to support multiple values.
+;; modified to use SRFI-9.
 
 ;; This module is documented in the Guile Reference Manual.
 
@@ -36,9 +36,8 @@
   #:export (delay
              lazy
              force
-             eager
+             eager)
-             promise?)
+  #:replace (delay force)
-  #:replace (delay force promise?)
   #:use-module (srfi srfi-9))
 
 (cond-expand-provide (current-module) '(srfi-45))
@@ -53,18 +52,16 @@
 (define-syntax-rule (lazy exp)
   (make-promise (make-value 'lazy (lambda () exp))))
 
-(define (eager . xs)
+(define (eager x)
-  (make-promise (make-value 'eager xs)))
+  (make-promise (make-value 'eager x)))
 
 (define-syntax-rule (delay exp)
-  (lazy (call-with-values
+  (lazy (eager exp)))
-            (lambda () exp)
-          eager)))
 
 (define (force promise)
   (let ((content (promise-val promise)))
     (case (value-tag content)
-      ((eager) (apply values (value-proc content)))
+      ((eager) (value-proc content))
       ((lazy)  (let* ((promise* ((value-proc content)))
                       (content  (promise-val promise)))        ; *
                  (if (not (eqv? (value-tag content) 'eager))   ; *

test-suite/tests/srfi-45.test

@@ -1,7 +1,6 @@
 ;;; -*- mode: scheme; coding: utf-8; -*-
 
-;; Copyright (C) 2010, 2013 Free Software Foundation, Inc.
+;; Copyright André van Tonder. All Rights Reserved.
-;; Copyright (C) 2003 André van Tonder. All Rights Reserved.
 ;;
 ;; Permission is hereby granted, free of charge, to any person
 ;; obtaining a copy of this software and associated documentation
@@ -259,43 +258,3 @@
 ;; Commented out since it takes too long
 #;
 (test-equal 300000000 (force (times3 100000000)))    ;==> bounded space
-
-
-;======================================================================
-; Test promise? predicate (non-standard Guile extension)
-
-(pass-if "promise? predicate"
-  (promise? (delay 1)))
-
-;======================================================================
-; Test memoization of multiple values (non-standard Guile extension)
-
-(with-test-prefix "Multiple values (non-standard)"
-
- (let ((promise (delay (values 1 2 3))))
-   (pass-if-equal "Multiple values delay"
-       '(1 2 3)
-     (call-with-values
-         (lambda () (force promise))
-       list)))
-
- (let ((promise (eager 1 2 3)))
-   (pass-if-equal "Multiple values eager"
-       '(1 2 3)
-     (call-with-values
-         (lambda () (force promise))
-       list)))
-
- (let ((promise (delay (values))))
-   (pass-if-equal "Zero values delay"
-       '()
-     (call-with-values
-         (lambda () (force promise))
-       list)))
-
- (let ((promise (eager)))
-   (pass-if-equal "Zero values eager"
-       '()
-     (call-with-values
-         (lambda () (force promise))
-       list))))