On 10/08/2011 10:12 AM, Matthias Felleisen wrote:

(1) I do not understand Neil's problem. Say I have module A and
want to protect its exports from abuses by clients, say module B,
why do you use define/contract at all? The define/contract form
is for splitting modules into module-lets -- in case your module
is too large and you can't manage invariants in your head.

Which now I see that you can *infer* from the docs, if you already sort of know this. They're kinda jagony. But now I understand, so thank you.

The thing is, define/contract has a huge advantage that contract-out doesn't have: it puts all the invariants at the function definition, right before the code that relies on them. I suppose I could get the same effect with a contract-out right before the function definition (or write a define/provide macro). But I think the style guidelines say this is bad, and I don't like scattering provides throughout code.

If you
believe that this is true for even small modules, I urge you to
use Typed Racket. That's the better solution and real soon now
TR will allow you to add contracts on top of types at provides.

I would love to, if not for all the keyword arguments. :( That is seriously the only thing keeping me from making PLoT into a typed library.

(2) I object to


because I think programmers should explicitly state what
they want (if they want something logical).

I can't explicitly say what I want right now, and I think it's logical.

Would the following be explicit enough?

    (provide (contract-out real-id))

    ; ... more code ...

    (define/contract (real-id x) (real? . -> . real?)

Or (provide (lift-contract real-id)) might be even better.

Neil T
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