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. 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.
Thanks
Dan
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