Not sure what the :scheme header argument might be or how to change it. However, changing the geiser-impl--implementation (changed order to make sure) and geiser-default-implementation seemed to do the trick. My bad overlooking this.

Thanks,
LB

On Sat, Aug 29, 2015 at 10:45 PM, Thomas S. Dye <tsd@tsdye.com> wrote:
Aloha Lawrence,

Lawrence Bottorff <borgauf@gmail.com> writes:

> I have a few schemes installed on my computer (MIT, guile, chicken), but
> when I run such code as this
>
> #+BEGIN_SRC scheme :session one
> (define (myadd x y)
>    (+ x y))
> #+END_SRC
>
> it works -- beautifully with multiple REPLs (as you name them in the
> :session) -- but it always grabs the guile. I'd like it to use chicken
> instead -- or maybe later MIT. I've got latest geiser installed as well
> that should handle chicken. How can I use chicken inside of orgmode scheme
> code blocks? Wild guess, guile is first on some list, i.e., path? babel
> customize didn't seem to have an entry for which flavor.

Looking at the code, there is a :scheme header argument that can
indicate what scheme implementation should be used.  Otherwise, it
appears to use geiser-impl--implementation, which a comment says is
defined in geiser-impl.el.  There is also geiser-default-implementation
and geiser-active-implementations from that same source.

hth,
Tom

--
Thomas S. Dye
http://www.tsdye.com