I've always liked define/contract because it guarantees the safety of the function from erroneous calls by other functions in the module, which helps with debugging and testing. It sounds like you think that's a bad move?
On Wed, Apr 7, 2021 at 4:35 PM Robby Findler <[email protected]> wrote: > > The short answer: you probably should use (provide (contract-out....)) > instead of define/contract. > > The slightly longer answer: when you write a contract, you are not just > describing what the legal inputs and outputs are, you are also establishing a > *boundary* between two regions of code. In the case of define/contract, you > are establishing a boundary between the function (here: f) and the module > that it contains (here the file "a.rkt"). In the case of (provide > (contract-out ...)) the boundary is between a.rkt and b.rkt. > > The slightly uncomfortable answer: it is my (not completely solid yet) > opinion that the boundary that is drawn for define/contract is perhaps not > the right / best one. In a theoretical/mathematical sense it is a completely > fine and completely defensible one. But it trips people up sometimes. (There > are examples others have posted in the past that are perhaps even stranger > than yours but boil down to the same specific design choice for > define/contract.) > > Robby > > > > On Wed, Apr 7, 2021 at 2:10 PM epi via Racket Users > <[email protected]> wrote: >> >> Hello Racket users, >> >> I am trying to understand a contract violation message that I am getting. >> Here is the file a.rkt: >> >> #lang racket >> (provide f) >> (define/contract (f a) >> (-> boolean? any/c) >> '()) >> >> and this is b.rkt: >> >> #lang racket >> (require "a.rkt") >> (f 3) >> >> >> I would expect that the caller is blamed for the contract violation, but the >> error message that I get is as follows: >> >> >> f: contract violation >> expected: boolean? >> given: 3 >> in: the 1st argument of >> (-> boolean? any/c) >> contract from: (function f) >> blaming: /home/epi/snippets/a.rkt >> (assuming the contract is correct) >> at: /home/epi/snippets/a.rkt:3.18 >> context...: >> /usr/share/racket/collects/racket/contract/private/blame.rkt:347:0: >> raise-blame-error >> >> /usr/share/racket/collects/racket/contract/private/arrow-higher-order.rkt:379:33 >> body of "/home/dan/snippets/blameme.rkt" >> >> So, I am a bit surprised that the error message blames the file a.rkt. >> What am I missing here? >> >> -- >> 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/149cfc632cd666ff1a92177dce90296b%40disroot.org. > > -- > 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/CAL3TdONLMx%3Dy_cgfDsY_k9L9yaX_touO52phiK9scziW_jGrOA%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/CAE8gKofSq%3DvzFV3jt3fkMbzMqV%3Dt9%2BHtj1y02Nsku_ZXF6%2BB5A%40mail.gmail.com.
