From a441402fb0fa55ed360f97a5d8856d2fe7aeb3d5 Mon Sep 17 00:00:00 2001
From: Masaya Tojo <masaya@tojo.tokyo>
Date: Sun, 25 Aug 2024 20:41:04 +0900
Subject: Add (qklib memoization) library

---
 qklib/memoization.scm | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 qklib/memoization.scm

diff --git a/qklib/memoization.scm b/qklib/memoization.scm
new file mode 100644
index 0000000..de97354
--- /dev/null
+++ b/qklib/memoization.scm
@@ -0,0 +1,53 @@
+;;; Copyright 2024 Masaya Tojo <masaya@tojo.tokyo>
+;;;
+;;; Licensed under the Apache License, Version 2.0 (the "License");
+;;; you may not use this file except in compliance with the License.
+;;; You may obtain a copy of the License at
+;;;
+;;;     http://www.apache.org/licenses/LICENSE-2.0
+;;;
+;;; Unless required by applicable law or agreed to in writing, software
+;;; distributed under the License is distributed on an "AS IS" BASIS,
+;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;;; See the License for the specific language governing permissions and
+;;; limitations under the License.
+
+(define-library (qklib memoization)
+  (export memoize memoize1)
+  (import (scheme base)
+          (scheme case-lambda)
+          (srfi 128))
+  (cond-expand
+    ((library (srfi srfi-146 hash))     ; for guile-srfi-146
+     (import (srfi srfi-146 hash)))
+    ((library (srfi 146 hash))
+     (import (srfi 146 hash))))
+  (begin
+    (define memoize
+      (case-lambda
+        ((f)
+         (memoize f (make-default-comparator)))
+        ((f comparator)
+         (let ((memo (hashmap comparator)))
+           (let memo-fix ((f f))
+             (lambda (args)
+               (hashmap-ref memo args
+                            (lambda ()
+                              (define result (apply (f (memo-fix f)) args))
+                              (set! memo (hashmap-set! memo args result))
+                              result))))))))
+
+    (define memoize1
+      (case-lambda
+        ((f)
+         (memoize1 f (make-default-comparator)))
+        ((f comparator)
+         (let ((memo (hashmap comparator)))
+           (let memo-fix ((f f))
+             (lambda (x)
+               (hashmap-ref memo x
+                            (lambda ()
+                              (define result ((f (memo-fix f)) x))
+                              (set! memo (hashmap-set! memo x result))
+                              result))))))))
+    ))
-- 
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