Re: [racket-users] define/contract for private functions

[Bogdan Popa]

> When I want to enable these private contracts (e.g. when running tests or
> debugging a problem) I simply change the source code of `def/c` so that it
> is wired up to `define/contract` and the contract is checked. Here is an
> example: http://pasterack.org/pastes/4224

You can run arbitrary code in macros so you could use environment
variables to achieve this.  For example:

(define-syntax-rule (def/c head contract body ...)
  (if (getenv "PRIVATE_CONTRACTS")
(define/contract head contract body ...)
(define head body ...)))

And then run your code with

env PRIVATE_CONTRACTS=x racket some-module.rkt

The drawbacks to this approach is it makes compilation significantly
slower and, once code is compiled (via raco setup, raco make or raco pkg
install), the flag stops having any effect -- the code is compiled
according to whatever the environment looks like at compile time and
then maintains that behavior until it is recompiled.

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[racket-users] define/contract for private functions

[Ryan Kramer]

I've found myself wanting to write contracts on private functions, but I 
don't want to pay the performance cost during normal operation. What I've 
been doing is making a `def/c` macro which looks exactly like 
`define/contract` but is wired up to `define` and discards the contract. 
When I want to enable these private contracts (e.g. when running tests or 
debugging a problem) I simply change the source code of `def/c` so that it 
is wired up to `define/contract` and the contract is checked. Here is an 
example: http://pasterack.org/pastes/4224

Manually changing the source code of `def/c` has worked fine so far, but I 
would love to be able to do something like "raco test 
-with-private-contracts (package1, package2) ./" instead.

I prefer this approach over putting the contracts in comments, because 
comments have less precise meaning and may become subtly inaccurate if the 
implementation of the function changes.

I wonder if other people want to write code the same way. If so, having a 
standard, shared `define/contract/private` could be useful. This would 
allow us to do things like
1) Build a contract-aware linter.
2) Build a "minimally intrusive type system." (This might also be called a 
"linter"; I'm not sure if there is a definite line separating the two.)
3) Better IDE support
4) If I suspect a package I am using has a bug, I might be able to confirm 
(but not deny) that suspicion by turning on private contracts for that 
package and seeing if a violation is reported.

So I guess if I'm the only one interested in this then just ignore me. If 
there's already work in this area, great! Please point me to it. But if 
there's interest and a need, I'd be happy to help however I can.

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