p.s. Contracts are not types. Even if you use define/contract, you may violate the contract on recursive calls. This is intentional.
On Nov 16, 2012, at 7:13 PM, Matthias Felleisen wrote: > > First cut: Contracts check cross-module invariants. That's why they establish > boundaries: > > http://doc.racket-lang.org/guide/contract-boundaries.html?q=contracts > > When a module M provides a function f with a contract, calls w/i M to f are > not checked. > > Second cut: if you know about contract regions, you can break modules into > several contract regions and thus force contract checks within a module. > > > > On Nov 16, 2012, at 6:59 PM, Harry Spier wrote: > >> Dear list members, >> >> Can someone explain why in the following cases only two out of the three >> cases and not all of them cause a contract violation. >> Thanks, >> Harry Spier >> >> #lang racket >> (provide/contract (amount positive?)) >> (define amount -7) >>> >> contract >> promised: positive? >> produced: -7 >> in: positive? >> contract from: anonymous-module >> blaming: anonymous-module >> >> BUT-------------------------------------- >> >> #lang racket >> (provide/contract [amount (-> positive?)]) >> (define (amount) -7) >> (amount) >>> >> No contract violation >> >> AND------------------------------------------- >> >> #lang racket >> >> (provide/contract [amount (-> positive?)]) >> (define (amount) -7) >> >> (module* main racket >> (require (submod "..")) >> (amount)) >> >>> >> amount: broke its contract >> promised: positive? >> produced: -7 >> in: the range of >> (-> positive?) >> contract from: >> c:\users\harry\ocr_project\contract-test.rkt >> blaming: >> c:\users\harry\ocr_project\contract-test.rkt >> at: c:\users\harry\ocr_project\contract-test.rkt:3.20 >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users
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