(define-syntax-rule (return/1 value)
value)
-(define %nothing ;nothingness
- (list 'this 'is 'nothing))
-
(define-syntax define-cache-procedure
(syntax-rules ()
"Define a procedure NAME that implements a cache using HASH-REF and
and RETURN are used to distinguish between multiple-value and single-value
returns."
((_ name hash-ref hash-set! call return)
- (define (name cache key thunk)
- "Cache the result of THUNK under KEY in CACHE, or return the
+ (define name
+ (let ((%nothing '(this is nothing)))
+ (lambda (cache key thunk)
+ "Cache the result of THUNK under KEY in CACHE, or return the
already-cached result."
- (let ((results (hash-ref cache key %nothing)))
- (if (eq? results %nothing)
- (let ((results (call thunk)))
- (hash-set! cache key results)
- (return results))
- (return results)))))
+ (let ((results (hash-ref cache key %nothing)))
+ (if (eq? results %nothing)
+ (let ((results (call thunk)))
+ (hash-set! cache key results)
+ (return results))
+ (return results)))))))
((_ name hash-ref hash-set!)
(define-cache-procedure name hash-ref hash-set!
call/mv return/mv))))