<HTML><BODY>It is maybe closer. But inside define-binary-class I also doesn't know the total number of init arguments. Because library user may give any superclass. And I don't know, how to get init arguments (or arity for of make-object for a given class) without calling make-object and reading the error message. Lake in case (define base% (class (super-new) (init-field param1 param2))) (define-binary-class db base% ((a u1) (b u2))) Maybe the problem doesn't have a solution. But I see class/c, which has init and init-fields clauses. Somehow it checks them... Thu, 5 Jun 2014 16:36:16 -0400 от Matthias Felleisen <matthias@ccs.neu.edu>: <blockquote style="border-left:1px solid #0857A6; margin:10px; padding:0 0 0 10px;"> <div id=""> <div class="js-helper js-readmsg-msg"> <style type="text/css"></style> <div> <base target="_self" href="https://e.mail.ru/"> <div id="style_14020005770000000444_BODY"> Sorry I am so slow. Contracts are first-class values. You could modify define-binary-class so that it also creates and defines a contract P that can be passed along to read-object. Then read-object can use P like this: > #lang racket > > (provide > a% a? > b% b? > (contract-out > (read-object (->i ((c? contract?) (c% any/c)) > #:rest [l (c?) (lambda (x) (apply c? x))] > (_ (c%) (is-a?/c c%)))))) > > (define a% (class object% [init-field x] (super-new))) > (define b% (class object% [init-field x y] (super-new))) > > (define a? (lambda x (and (= (length x) 1) (andmap number? x)))) > (define b? (lambda x (and (= (length x) 2) (andmap number? x)))) > > (define (read-object __c c% . x) > (apply make-object c% x)) Then you get exactly what you want and pretty precise checking: > % !! > racket > Welcome to Racket v6.0.1.11. > > (require "foo.rkt") > foo.rkt:9:23: is-a/c?: unbound identifier in module > in: is-a/c? > context...: > standard-module-name-resolver > /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7 > > (require "foo.rkt") > foo.rkt:9:31: c%: unbound identifier in module > in: c% > context...: > standard-module-name-resolver > /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7 > > (require "foo.rkt") > > ( read-object b? b% 10 20 ) > (object:b% ...) > > ( read-object b? b% 10 ) > read-object: contract violation > expected: ...vn/2HtDP/foo.rkt:8:34 > given: '(10) > in: the l argument of > (->i > ((c? contract?) (c% any/c)) > #:rest > (l (c?) (lambda (x) (apply c? x))) > (_ (c%) (is-a?/c c%))) > contract from: > /Users/matthias/svn/2HtDP/foo.rkt > blaming: top-level > at: /Users/matthias/svn/2HtDP/foo.rkt:7.5 > context...: > /Users/matthias/plt/racket/collects/racket/contract/private/blame.rkt:143:0: raise-blame-error16 > arg-checker > /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7 > > ( read-object a? a% 10 ) > (object:a% ...) > > ( read-object a? a% 10 20) > read-object: contract violation > expected: ...vn/2HtDP/foo.rkt:8:34 > given: '(10 20) > in: the l argument of > (->i > ((c? contract?) (c% any/c)) > #:rest > (l (c?) (lambda (x) (apply c? x))) > (_ (c%) (is-a?/c c%))) > contract from: > /Users/matthias/svn/2HtDP/foo.rkt > blaming: top-level > at: /Users/matthias/svn/2HtDP/foo.rkt:7.5 > context...: > /Users/matthias/plt/racket/collects/racket/contract/private/blame.rkt:143:0: raise-blame-error16 > arg-checker > /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7 If you want to make sure that a? and a% come together, you can package them up in structs. If you just want to make sure that these contracts come from your binary class module, you can hide them in applicable structs or something like that. Am I getting closer? -- Matthias On Jun 5, 2014, at 4:15 PM, Roman Klochkov <<a href="/compose?To=kalimehtar@mail.ru">kalimehtar@mail.ru</a>> wrote: > I don't create classes. I provide a function read-object, so user can do > > (require binary-class) > (define base% (class (super-new) (init-field param1 param2))) > (define-binary-class db base% ((a u1) (b u2))) > > (define data (read-object db my-file data-param1 data-param2) > > And I try to make a contract, so when he made an error in last call and wrote > > (define data (read-object db my-file data-param1)), then error message whould blame read-object, not `instantiate' > > Thu, 5 Jun 2014 16:08:39 -0400 от Matthias Felleisen <<a href="/compose?To=matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>>: > > Can't you use is-a?/c like this: > > > #lang racket > > > > (provide > > a% > > b% > > (contract-out > > (read-object (case-> > > [-> (is-a?/c a%) number? number?] > > [-> (is-a?/c b%) number? number? number?])))) > > > > (define a% (class object% (super-new))) > > (define b% (class object% (super-new))) > > > > (define read-object > > (case-lambda > > [(a x) x] > > [(b x y) (+ x y)])) > > > and use this module like this: > > > % racket > > Welcome to Racket v6.0.1.11. > > > (require "foo.rkt") > > > (read-object (new a%) 10) > > 10 > > > (read-object (new a%) 10 20) > > read-object: contract violation > > expected: (is-a?/c b%) > > given: (object:a% ...) > > in: the domain of > > the 2nd case of > > (case-> > > (-> (is-a?/c a%) number? number?) > > (-> (is-a?/c b%) number? number? number?)) > > contract from: > > /Users/matthias/svn/2HtDP/foo.rkt > > blaming: top-level > > at: /Users/matthias/svn/2HtDP/foo.rkt:7.5 > > context...: > > /Users/matthias/plt/racket/collects/racket/contract/private/blame.rkt:143:0: raise-blame-error16 > > /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7 > > > (read-object (new b%) 10 20) > > 30 > > > (read-object (new b%) 10) > > read-object: contract violation > > expected: (is-a?/c a%) > > given: (object:b% ...) > > in: the domain of > > the 1st case of > > (case-> > > (-> (is-a?/c a%) number? number?) > > (-> (is-a?/c b%) number? number? number?)) > > contract from: > > /Users/matthias/svn/2HtDP/foo.rkt > > blaming: top-level > > at: /Users/matthias/svn/2HtDP/foo.rkt:7.5 > > context...: > > /Users/matthias/plt/racket/collects/racket/contract/private/blame.rkt:143:0: raise-blame-error16 > > /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7 > > > > On Jun 5, 2014, at 3:19 PM, Roman Klochkov <<a href="/compose?To=kalimehtar@mail.ru">kalimehtar@mail.ru</a>> wrote: > > > (define (read-object binary-class in . args) > > (send (apply make-object binary-class args) read in)) > > > > read-object takes a class as a first arg, and additional arguments to make an object of that class. > > > > I can't make case-> because I don't know j,ject of what (user-defined) class will be created with the function by user of my library. > > > > This case is described in Racket Guide 7,3.9 <a href="http://docs.racket-lang.org/guide/contracts-general-functions.html#%28part._contracts-no-domain%29" target="_blank">http://docs.racket-lang.org/guide/contracts-general-functions.html#%28part._contracts-no-domain%29</a> , where recommended to use unconstrained-domain-> with procedure-arity-includes? , but it doesnt' work with make-object > > > > Thu, 5 Jun 2014 14:51:21 -0400 от Matthias Felleisen <<a href="/compose?To=matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>>: > > > > From what I understand now, you want a contract for a function that creates objects from a variable number of arguments. If you write your module interface like this, > > > > > #lang racket > > > > > > (provide > > > (contract-out > > > (read-object (case-> > > > [-> 'a number? number?] > > > [-> 'b number? number? number?])))) > > > > > > (define read-object > > > (case-lambda > > > [(a x) x] > > > [(b x y) (+ x y)])) > > > > you can get checked variable-arity behavior: > > > > > Welcome to Racket v6.0.1.11. > > > > (require "foo.rkt") > > > > (read-object 'a 10) > > > 10 > > > > (read-object 'b 10 20) > > > 30 > > > > (read-object 'b 10) > > > read-object: contract violation > > > expected: (quote a) > > > given: 'b > > > in: the domain of > > > the 1st case of > > > (case-> > > > (-> 'a number? number?) > > > (-> 'b number? number? number?)) > > > contract from: > > > /Users/matthias/svn/2HtDP/foo.rkt > > > blaming: top-level > > > at: /Users/matthias/svn/2HtDP/foo.rkt:5.5 > > > context...: > > > /Users/matthias/plt/racket/collects/racket/contract/private/blame.rkt:143:0: raise-blame-error16 > > > /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7 > > > > (read-object 'a 10 20) > > > read-object: contract violation > > > expected: (quote b) > > > given: 'a > > > in: the domain of > > > the 2nd case of > > > (case-> > > > (-> 'a number? number?) > > > (-> 'b number? number? number?)) > > > contract from: > > > /Users/matthias/svn/2HtDP/foo.rkt > > > blaming: top-level > > > at: /Users/matthias/svn/2HtDP/foo.rkt:5.5 > > > context...: > > > /Users/matthias/plt/racket/collects/racket/contract/private/blame.rkt:143:0: raise-blame-error16 > > > /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7 > > > > > > I think you can use ->i contracts inside of the case-> clauses if you need more precision. > > > > If I am still misunderstanding your question, sorry. > > > > -- Matthias > > > > > > > > > > > > > > > > > > > > -- > > > > Roman Klochkov > > > > > > > > > > > > -- > > > Roman Klochkov > > > > > > > > -- > > Roman Klochkov > > > > -- > Roman Klochkov </div> <base target="_self" href="https://e.mail.ru/"> </div> </div> </div> </blockquote> -- Roman Klochkov </BODY></HTML>