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;; Defines simple memoization functions. Currently it uses an alist -
;; we should change that to a hash. Also we want the cache to expire
;; after some time. memoize2 is now a separate function to deal
;; specifically with two return values. That is not ideal either.
;; Basically lifted from
;; https://lispdreams.wordpress.com/2016/04/08/lisp-memoization-techniques/
(define-module (gn cache memoize)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-13) ; hash table for memoize
#:use-module (srfi srfi-11) ; let-values
#:export (memoize
memoize2))
(define (memoize f)
"Simple memoize just uses alists at this point and does not expire"
(let ((result-table '()))
(lambda (. args)
(let ((cache-value (assoc args result-table)))
(if cache-value
(cdr cache-value)
(let ((result (apply f args)))
(set! result-table
(alist-cons args result result-table)) result))))))
(define (memoize2 f)
"Simple memoize functions that returns values pair and uses alists at this point and does not expire"
(let ((result-table '()))
(lambda (. args)
(let ((c (assoc args result-table)))
(if c
(values (car (cdr c)) (car (cdr (cdr c))))
(let-values (((r1 r2) (apply f args)))
(set! result-table
(alist-cons args (list r1 r2) result-table)) (values r1 r2)))))))
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