From c90cc88da76cefbc30897042ec88eff5cf0d6264 Mon Sep 17 00:00:00 2001
From: Christopher Baines <mail@cbaines.net>
Date: Wed, 29 Jan 2025 16:16:35 +0000
Subject: [PATCH] Add fibers-promise-result-available?

---
 knots/promise.scm |  8 +++++++-
 tests/promise.scm | 10 +++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/knots/promise.scm b/knots/promise.scm
index 3eb0a81..235640b 100644
--- a/knots/promise.scm
+++ b/knots/promise.scm
@@ -24,7 +24,8 @@
   #:use-module (fibers conditions)
   #:export (fibers-delay
             fibers-force
-            fibers-promise-reset))
+            fibers-promise-reset
+            fibers-promise-result-available?))
 
 (define-record-type <fibers-promise>
   (make-fibers-promise thunk values-box evaluated-condition)
@@ -76,3 +77,8 @@
 (define (fibers-promise-reset fp)
   (atomic-box-set! (fibers-promise-values-box fp)
                    #f))
+
+(define (fibers-promise-result-available? fp)
+  (let ((val (atomic-box-ref (fibers-promise-values-box fp))))
+    (not (or (eq? val #f)
+             (eq? val 'started)))))
diff --git a/tests/promise.scm b/tests/promise.scm
index b7dec73..1c0e235 100644
--- a/tests/promise.scm
+++ b/tests/promise.scm
@@ -13,8 +13,16 @@
                     (* i 2))))
                (iota 10))))
 
+     (assert-equal
+      #f
+      (fibers-promise-result-available? (car promises)))
+
      (assert-equal
       90
-      (apply + (fibers-map fibers-force promises))))))
+      (apply + (fibers-map fibers-force promises)))
+
+     (assert-equal
+      #t
+      (fibers-promise-result-available? (car promises))))))
 
 (display "promise test finished successfully\n")