Re: [Scheme-reports] Seeking review of sets and hash tables proposals

[Alex Shinn <alexshinn@x>]

On Sun, May 26, 2013 at 7:49 AM, Alexey Radul <axch@x> wrote:

2) Universal lookup procedure

I am fond of the following universal lookup procedure [1]:
  (hash-table-search table key
    (lambda (value update remove)
      ...)
    (lambda (insert)
      ...))

This is very nice, and it's important to provide fundamental

operations such as this which allow arbitrary ref+update logic

without requiring the hash to be recomputed.  This is not

possible in either the SRFI-69 or R6RS APIs (though an impl

may cache one or more recently hashed values).

I also think the following utility is nice, as there is no other

existing utility to use a hash-table as a cache with a single

operation:

  (hash-table-ref/cache! table key thunk)

  => (hash-table-search

      table key

      (lambda (value update remove)

        value)

      (lambda (insert)

        (let ((res (thunk)))

          (insert res)

          res)))

-- 

Alex

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