[Guile-commits] GNU Guile branch, srfi-41, updated. v2.0.7-211-g22ee2f7

[Chris K. Jester-Young]

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http://git.savannah.gnu.org/cgit/guile.git/commit/?id=22ee2f7dc985ffadaf5603256eab94a8c650759c

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- Log -----------------------------------------------------------------
commit 22ee2f7dc985ffadaf5603256eab94a8c650759c
Author: Chris K. Jester-Young <address@hidden>
Date:   Tue Mar 19 17:46:51 2013 -0400

    Simplify stream? so that the promise doesn't need forcing.
    
    * module/srfi/srfi-41.scm: The major change here is that instead of
      using (srfi srfi-45) directly, we use an independent promise type,
      so that anything that's that promise type are going to be streams.
      Currently, we use copy-and-paste to create this independent type,
      just as in the reference implementation; it's unpleasant, but we
      hope to find a better way soon.
      (stream?): Define as stream-promise?.
      (stream-null): Use stream-eager rather than stream-delay. I don't
      see why the reference implementation chose to use delay there.
      (stream-unfolds): Now that stream? doesn't prematurely force the
      stream, it's possible to use stream-append to join up the streams.

commit 9069f1c18eedfe46e2a3d1d2bc5ff9ba14a9a02a
Author: Chris K. Jester-Young <address@hidden>
Date:   Tue Mar 19 17:11:15 2013 -0400

    Fix typo. Thanks to Mark H. Weaver for the catch.
    
    * module/srfi/srfi-41.scm (stream-append): Fix typo.

-----------------------------------------------------------------------

Summary of changes:
 module/srfi/srfi-41.scm |   49 ++++++++++++++++++++++++++++++++++++++--------
 1 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/module/srfi/srfi-41.scm b/module/srfi/srfi-41.scm
index 91d2c67..9e82c99 100644
--- a/module/srfi/srfi-41.scm
+++ b/module/srfi/srfi-41.scm
@@ -28,9 +28,6 @@
   #:use-module (srfi srfi-8)
   #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-26)
-  #:use-module ((srfi srfi-45)
-                #:select (lazy eager delay force promise?)
-                #:renamer (symbol-prefix-proc 'stream-))
   #:use-module (ice-9 match)
   #:export (stream-null stream-cons stream? stream-null? stream-pair?
             stream-car stream-cdr stream-lambda define-stream
@@ -84,12 +81,47 @@
     ((_ name syntax)
      (define-syntax name syntax))))
 
+;;; Copy-and-paste of Mark H. Weaver's version of SRFI 45. Once we have
+;;; better support for creating an independent promise type, we'll use
+;;; that instead.
+
+(define-record-type stream-promise (make-stream-promise val) stream-promise?
+  (val stream-promise-val stream-promise-val-set!))
+
+(define-record-type stream-value (make-stream-value tag proc) stream-value?
+  (tag stream-value-tag stream-value-tag-set!)
+  (proc stream-value-proc stream-value-proc-set!))
+
+(define-syntax-rule (stream-lazy exp)
+  (make-stream-promise (make-stream-value 'lazy (lambda () exp))))
+
+(define (stream-eager . xs)
+  (make-stream-promise (make-stream-value 'eager xs)))
+
+(define-syntax-rule (stream-delay exp)
+  (stream-lazy (call-with-values
+                   (lambda () exp)
+                 stream-eager)))
+
+(define (stream-force promise)
+  (let ((content (stream-promise-val promise)))
+    (case (stream-value-tag content)
+      ((eager) (apply values (stream-value-proc content)))
+      ((lazy)  (let* ((promise* ((stream-value-proc content)))
+                      (content  (stream-promise-val promise)))
+                 (if (not (eqv? (stream-value-tag content) 'eager))
+                     (begin (stream-value-tag-set! content
+                                                   (stream-value-tag 
(stream-promise-val promise*)))
+                            (stream-value-proc-set! content
+                                                    (stream-value-proc 
(stream-promise-val promise*)))
+                            (stream-promise-val-set! promise* content)))
+                 (stream-force promise))))))
+
 ;;; Primitive stream functions and macros: (streams primitive)
 
-(define (stream? obj)
-  (or (stream-pair? obj) (stream-null? obj)))
+(define stream? stream-promise?)
 
-(define stream-null (stream-delay '(stream . null)))
+(define stream-null (stream-eager '(stream . null)))
 
 (define (stream-null? obj)
   (and (stream-promise? obj)
@@ -159,7 +191,7 @@
     (reverse! (first-value (stream-fold-aux xcons '() strm n))))))
 
 (define (stream-append . strms)
-  (must-every stream? strms 'stread-append "non-stream argument")
+  (must-every stream? strms 'stream-append "non-stream argument")
   (stream-let recur ((strms strms))
     (if (null? strms) stream-null
         (let ((strm (car strms)))
@@ -403,8 +435,7 @@
       (() stream-null)
       (#f (tail))
       ((item) (stream-cons item (tail)))
-      ;; Can't use stream-append, since the call to tail must be delayed.
-      ((? list? items) (stream-concat (stream (list->stream items) (tail))))))
+      ((? list? items) (stream-append (list->stream items) (tail)))))
 
   (must procedure? gen 'stream-unfolds "non-procedural argument")
   (let ((genstrm (generator-stream seed)))


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