[racket] (define (f (x y)) body) when y has a previous definition

The "y" in your program is the default value of the optional argument
'x'.  Does this help clarify?

Robby

On Mon, Jun 23, 2014 at 8:21 AM, Joshua TAYLOR <joshuaaaron at gmail.com> wrote:
> I was answering this Stack Overflow question [1], and came across this
> bizarre (to me, anyhow) behavior (REPL transcript from Dr.Racket)
>
>
> Welcome to DrRacket, version 5.3 [3m].
> Language: racket; memory limit: 128 MB.
>> (define y 2)
>> (define (f (x y))
>     (print x)
>     (print y))
>> (f 1)
> 12
>
>
> Is this expected?  If y isn't defined previously, then the definition
> is accepted in the REPL, but trying to call (f 1) results in an error:
>
>
> Welcome to DrRacket, version 5.3 [3m].
> Language: racket; memory limit: 128 MB.
>> (define (f (x y))
>     (print x)
>     (print y))
>> (f 1)
> 1. . y: undefined;
>  cannot reference an identifier before its definition
>
>
> Putting the definition in the definitions pane and Ctrl-R / Racket>Run
> gives an error:
>
>
> (X). y: unbound identifier in module in: y
>
>
> What's going on here?  The definition doesn't seem to be a legal form
> based on the syntax given in the documentation, but the system's still
> accepting it, and with varying behaviors.
>
> //JT
>
>
> [1] http://stackoverflow.com/q/24365591/1281433
>
> --
> Joshua Taylor, http://www.cs.rpi.edu/~tayloj/
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