Contracts really are like business contracts. They are between two distinct parties; they are not by a party on itself.
On occasion, you really do want to wish to break the contract inside a module. This is well-known in the OO world, and it is often called the re-entrance problem. Say you want a balanced tree object. Imagine it has a method with a contract that requires 'balanced'ness but is also called internally. Perhaps you don't need/wish to balance for internal calls. So you do -- and you don't get caught. Contracts impose a run-time cost. To make the cost reasonable, we trust the programmer and we let the programmer know that we trust him. On Nov 16, 2012, at 7:52 PM, Galler wrote: >> >> Even if you use define/contract, you may violate the contract on recursive > calls. This is intentional. >> > > Thanks. > > I hadn't run into that behavior before and wasn't aware. > > Could you possibly elaborate on the thinking wrt this design choice? > > (define/contract (my-natural-number n) > (-> exact-positive-integer? any/c) > (print n) (newline) > (my-natural-number (sub1 n))) > > (my-natural-number 1) > 1 > 0 > -1 > -2 > -3 > -4 > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users
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____________________ Racket Users list: http://lists.racket-lang.org/users
