# [plt-scheme] signed unit syntax

Hi all,
I'm trying to get a handle around some of the syntax for signed units
and have attached a simple toy example to show where I'm stuck.
In the example, there are two units one that performs some simple
computation and one that displays formatted output. I have a function
called _output-sqrt-sum-squares_ which consumes the values to submit
to the computation and tries to run the compuation and output the
result.
The error I'm getting is
>* reference to undefined identifier: output
*Clearly a lack of understanding on my part.
Thanks in advance for any help!
Cheers,
David
(require (lib "unitsig.ss"))
(define-signature c^ (computation))
(define-signature o^ (output))
(define [email protected]
(unit/sig c^
(import)
(define square
(lambda (x) (* x x)))
(define computation
(lambda (x y)
(+ (square x) (square y))))))
(define [email protected]
(unit/sig o^
(import)
(define output
(lambda (v)
(printf "value = ~a~n" v)))))
(define output-sqrt-sum-squares
(lambda (x y)
(invoke-unit/sig
(compound-unit/sig
(import)
(link
(COMP : c^ ([email protected]))
(OUT : o^ ([email protected])))
(export (open COMP) (open OUT))))
(output (distance x y)))) ; *** I don't know how to make this procedure call ***
(output-sqrt-sum-squares 2 4)