On Jul 20, 2014, at 1:56 PM, Jon Zeppieri wrote: > I feel like this has come up before, but I can't seem to find the > discussion in the archive. I have a procedure that needs to perform a > fairly expensive computation which is needed both for checking the > inputs and for producing output. I'd like to avoid computing it twice, > and I'd also like to use contracts to check the inputs. Is there any > reasonable way to do this?
No. The contract system is designed so that the contractual computations are in principle independent from the 'mutator' computations. > The code is like this: > > (define (do-stuff x y z) > (define important-value (expensive x y z)) > ... do stuff with important-value ...) > > (provide/contract > [do-stuff (->i [x ...] [y ...] [z (x y) > contract-that-depends-on-important-value]) [result ...])]) > > > I could memoize the expensive computation, but that would require > something like an LRU cache to avoid memory problems, and I'd rather > not have to worry about that. > > Alternatively, I could shift things around so that the contract is on > the procedure that generates important-value, but then blame reporting > would be incorrect. > > Any ideas? Define a syntactic abstraction that spans contracts and 'mutators'. -- Matthias ____________________ Racket Users list: http://lists.racket-lang.org/users
