(First off, this is really cool and I've wanted something like this for a while)

It would be especially nice if there was a #lang envy:

#lang envy
aws-access-key-id
aws-secret-access-key
[foo-enabled? #:name "FOO_ENABLED" #:default #f]

Which would be equivalent to:

#lang typed/racket/base
(require envy)
(define/provide-environment
  aws-access-key-id
  aws-secret-access-key
  [foo-enabled? #:name "FOO_ENABLED" #:default #f]

And it would be even nicer if it used syntax that cooperated with sweet expressions:

#lang sweet-exp envy
aws-access-key-id
aws-secret-access-key
foo-enabled? #:name "FOO_ENABLED" #:default #f

I should be able to do this:

(define-environment
  [logging-enabled? : Boolean])

Sometimes I'd like to do something reflectively over all bindings defined in a #lang envy module, like write them to a file, compute a signature of the current config, or store them in some global mutable data structure. It would be nice if #lang envy defined a hash table mapping symbols to the parsed env values.

When debugging issues in complex apps I find it helpful to know exactly what configuration the app is in. Would it be a useful feature to have something like a #:debug or #:log flag that printed out messages on app startup about the configuration?

It should be possible to have a set of environment variables that are required if another environment variable is #t, but use default values when it is #f.

It would be nice to have a custom coertion/parsing function beyond the generic type based ones. Something like:

(define/provide-environment [id #:coerse my-parse])

This would allow types beyond the default ones supported.