On Wed, Apr 26, 2017 at 12:48 PM, David Storrs <david.sto...@gmail.com> wrote:
> On Wed, Apr 26, 2017 at 12:21 AM, Jon Zeppieri <zeppi...@gmail.com> wrote:
>> I don't know that there's a right way, but if your functions are
>> nullary, then promises are a decent fit:
>> (define conf
>>   (delay
>>     (with-input-from-file ...)))
>> Then just (force conf) whenever you want the value.
> Yeah, that works well.  Thanks!
> Any thoughts on how to do it for non-nullary functions?

The more complicated your function signatures get, the more worthwhile
it will be to use the memoize package. But for, say, unary functions
you can easily use a hash table:

#lang racket

(define read-conf
  (let ([h (make-hash)])
    (λ (arg)
      (hash-ref! h
                 (thunk ...)))))

You can extend this to multiple arguments by using lists as keys, if
you want. Of course, you need to make sure that `equal?` is usefully
defined on your argument types.

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