[plt-scheme] signed unit syntax

Hello David

I believe you just need the expression inside the old friend the begin 
form then the compound-unit gets invoked before its called:

(define output-sqrt-sum-squares
    (lambda (x y)
      (begin
        (invoke-unit/sig
         (compound-unit/sig
           (import)
           (link
            (COMP : c^ (sqrt-sum-squares@))
            (OUT : o^ (simple-output@)))
           (export (open COMP) (open OUT))))
        (output (computation x y)))))

Presume you mean to call computation rather than distance as well :-)  

Then at the prompt you can call the function:

 > (output-sqrt-sum-squares 3 4)
value = 25
 >


Best wishes

Stephen Tetley

David J. Neu wrote:

>  For list-related administrative tasks:
>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>
>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 sqrt-sum-squares@
>  (unit/sig c^
>    
>    (import)
>    
>    (define square
>      (lambda (x) (* x x)))
>    
>    (define computation
>      (lambda (x y)
>        (+ (square x) (square y))))))
>
>(define simple-output@
>  (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^ (sqrt-sum-squares@))
>        (OUT : o^ (simple-output@)))
>       (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)
>
>
>
>  
>