At Tue, 1 Apr 2014 02:29:17 -0400 (EDT), Daniel Feltey wrote: > The define-signature form allows define-values and define-values-for-export > forms in its body. According to the documentation the define-values form > should > prefix any unit that imports the signature, and define-values-for-export > should > suffix any unit that exports the signature, but the actual behavior doesn't > seem to match the documentation. > > I can define the following signature and unit: > > (define-signature x^ > ((define-values-for-export (x) 5) > x > )) > > (define x@ > (unit (import) > (export x^))) > > (define-values/invoke-unit x@ (import) (export x^)) > > This makes sense to me, because the definition for x is available within the > x@ > unit, but it must also be listed in the signature by name in order to > actually > export the value, so that x is defined when invoking the unit with > define-values/invoke-unit. > > What confuses me is that I can also define the following signature and unit: > > (define-signature y^ > ((define-values (y) 5))) > > (define y@ > (unit (import) > (export y^))) > > (define-values/invoke-unit y@ (import) (export y^)) > > This does introduce a binding for y with the value 5, but I don't understand > why.
A `define-values` in a signature adds a definition to any *importing* context (in contrast to `define-values-for-export` which adds a definition in any *exporting* context). The `define-values/invoke-unit` form "imports" the signature into the definition context. > Since the y^ signature is being exported instead of imported I expected > that the value of y should not be available in the y@ unit, and furthermore > there is no need to declare y in the signature as a variable which the unit > must define. So why is it the case that this unit defines and exports the > value > of y, when according to the documentation this shouldn't happen. As you say, `y` isn't bound in the unit `y@` by the export of `y^`. With the `define-values/invoke-unit` form in the same context, though, the unit `y@` will be able to refer to `y`, just like any other binding in the unit's environment. ____________________ Racket Users list: http://lists.racket-lang.org/users
