> (require "simple-factory-unit.rkt") > (invoke-unit simple-factory@)
The invoke-unit form does not make the body definitions available, however, so we cannot build any toys with this factory. The define-values/invoke-unit form binds the identifiers of a signature to the values supplied by a unit (to be invoked) that implements the signature:
> (define-values/invoke-unit/infer simple-factory@)
> (build-toys 3)
(list (toy 'blue) (toy 'blue) (toy 'blue))
Since simple-factory@ exports the toy-factory^ signature, each identifier in toy-factory^ is defined by the define-values/invoke-unit/infer form. The /infer part of the form name indicates that the identifiers bound by the declaration are inferred from simple-factory@.
Now that the identifiers in toy-factory^ are defined, we can also invoke toy-store@, which imports toy-factory^ to produce toy-store^:
> (require "toy-store-unit.rkt") > (define-values/invoke-unit/infer toy-store@) > (get-inventory)
> (stock! 2) > (get-inventory)
(list (toy 'green) (toy 'green))
Again, the /infer part define-values/invoke-unit/infer determines that toy-store@ imports toy-factory^, and so it supplies the top-level bindings that match the names in toy-factory^ as imports to toy-store@.