From 75111332a9d1f3038dd686ca7f7ba75300ea1022 Mon Sep 17 00:00:00 2001
From: Eduardo Julian
Date: Wed, 25 Jan 2017 20:31:39 -0400
Subject: - Added thunks (lazy evaluation).

---
 stdlib/source/lux/codata/thunk.lux | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 stdlib/source/lux/codata/thunk.lux

(limited to 'stdlib/source')

diff --git a/stdlib/source/lux/codata/thunk.lux b/stdlib/source/lux/codata/thunk.lux
new file mode 100644
index 000000000..2c0db0db5
--- /dev/null
+++ b/stdlib/source/lux/codata/thunk.lux
@@ -0,0 +1,38 @@
+##  Copyright (c) Eduardo Julian. All rights reserved.
+##  This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
+##  If a copy of the MPL was not distributed with this file,
+##  You can obtain one at http://mozilla.org/MPL/2.0/.
+
+(;module:
+  lux
+  (lux [io]
+       (control monad)
+       (concurrency ["A" atom])
+       [compiler]
+       (macro ["s" syntax #+ syntax:])))
+
+(type: #export (Thunk a)
+  (-> [] a))
+
+(def: #hidden (freeze' generator)
+  (All [a] (-> (-> [] a) (-> [] a)))
+  (let [cache (: (A;Atom (Maybe ($ +0)))
+                 (A;atom #;None))]
+    (lambda [_]
+      (case (io;run (A;get cache))
+        (#;Some value)
+        value
+
+        _
+        (let [value (generator [])]
+          (exec (io;run (A;compare-and-swap _ (#;Some value) cache))
+            value))))))
+
+(syntax: #export (freeze expr)
+  (do @
+    [g!arg (compiler;gensym "")]
+    (wrap (list (` (freeze' (lambda [(~ g!arg)] (~ expr))))))))
+
+(def: #export (thaw thunk)
+  (All [a] (-> (Thunk a) a))
+  (thunk []))
-- 
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