> > My understanding is that contract-out only provides protection against > inappropriate calls from clients *outside* the module, whereas > define/contract enforces the contract against everyone, including things > inside the module. Do I have that right? >
I think that's correct. Note though that the implication is that define/contract could produce a much more expensive code, especially for recursive function, since it will need to check against the contract for every iteration. > On a related topic, I don't understand the concept of positive and > negative blame. Can someone fill me in? > I always forget which is positive and negative, so I won't use the terms here (and too lazy to lookup). But roughly, suppose you attach a function contract (-> number? string?) to a function value, then there are mainly two ways things could go wrong. 1. Client uses the function incorrectly by calling it with non-number. 2. The function itself returns a non-string. A blame would indicate whose party is at fault when a contract is violated--caller or the function itself. > > >> Here's an example to play with. Submod A provides two functions: f0 is >> made with define/contract and f1 with contract-out. >> >> ``` >> #lang racket >> >> (module A racket >> (define/contract (f0 x) >> (-> natural? natural?) >> x) >> >> (define (f1 x) >> x) >> >> (provide f0) >> (provide (contract-out [f1 (-> natural? natural?)]))) >> >> (module B racket >> (require (submod ".." A)) >> (f0 'hello) >> #;(f1 'hello)) >> >> (require 'B) >> ``` >> >> If B makes a mistake with f0, the error blames submod A. >> But if B makes a mistake with f1, the error blames B. >> >> >> The contract library makes these blame errors internally. I don't >> think there's any way to customize short of using `contract` directly. >> >> > Is it related to this part of the documentation of `contract-out` >> > ( >> https://docs.racket-lang.org/reference/attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._contract-out%29%29 >> ) >> > - which I admittedly don't understand: >> > >> > "The implementation of contract-out >> > < >> https://docs.racket-lang.org/reference/attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._contract-out%29%29 >> > >> > uses syntax-property >> > < >> https://docs.racket-lang.org/reference/stxprops.html#%28def._%28%28quote._~23~25kernel%29._syntax-property%29%29 >> > >> > to attach properties to the code it generates that records the syntax of >> > the contracts in the fully expanded program. Specifically, the symbol ' >> > provide/contract-original-contract is bound to vectors of two elements, >> the >> > exported identifier and a syntax object for the expression that produces >> > the contract controlling the export." >> >> I was only thinking of the "blaming: ...." part of error messages. >> >> Both define/contract and contract-out can print the whole contract; I >> don't think this syntax-property gives contract-out any advantage >> >> (Sadly, the whole contract is sometimes too big to help me find a >> problem.) >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/racket-users/CAFUu9R5BMG5ZFVrddrJ-6uceV%2B3936ZudE-8ESObycw9B%2BRjcg%40mail.gmail.com >> . >> > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/racket-users/CAE8gKof2M%2BHuCf%2B2hfTKbVxCxGEb1Vtx%2BaXehYNZXhttpgMNPA%40mail.gmail.com > <https://groups.google.com/d/msgid/racket-users/CAE8gKof2M%2BHuCf%2B2hfTKbVxCxGEb1Vtx%2BaXehYNZXhttpgMNPA%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CADcuegskOV0cOQ8xYjTmbED2XA8dvZj9OkY_aFP0_7d28Lho3g%40mail.gmail.com.
