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 <ro...@cs.northwestern.edu> 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 > <racket-users@googlegroups.com> 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 racket-users+unsubscr...@googlegroups.com. >> 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 racket-users+unsubscr...@googlegroups.com. > 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 racket-users+unsubscr...@googlegroups.com. 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.
