I'm not clear on what constraints you're working under with respect to
modules, but hopefully you can adapt this to your needs.

One option is to use a combination of `define-module-boundary-contract` (or
`define/contract`) and `define-match-expander` to bind a name that can be
used as a contracted constructor and as a match pattern. (If you want to
extend the struct type, though, you still need to use the real one.)

Another option would be to "forge" a new compile-time struct-info based on
the original struct-info but replacing the constructor.

Minimally tested sample implementations attached.

Ryan


On Mon, May 10, 2021 at 12:23 AM Sage Gerard <s...@sagegerard.com> wrote:

> I have a project with 57 prefab structure types. I need to construct
> instances using a *local* contract (module level contracts do not fit my
> needs here). Since I cannot define guards, the solution is easy enough.
> (struct foo (num) #:prefab)
> (define/contract make-foo (-> real? foo?) foo)
>
> Problem: I already have a few hundred constructor calls without contracts.
> I could either A) rewrite them all to use contracted constructors, or B)
> attach local contracts in a sweet spot so that I don't have to rewrite
> anything else.
>
> I prefer option B, but it doesn't look like I can attach a local contract
> to a constructor with `struct` alone, or even with an impersonator. When I
> hack around to rebind or hide the constructor's identifier, I break
> compatibility with `match` and `defstruct*`.
>
> If you were in my position, what would you do?
> --
>
> ~slg
>
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