On May 27th Jüergen wrote:
"Note that there are some subtle differences between IBM APL2 and GNU APL
when localizing ⎕-vars. In IBM APL2 they are undefined after localizing them.
In GNU APL they are pre-initialized with their respective default values. This
gives simpler (and therefore faster code) because no check for validity is needed
for the variables themselves, but also for the many internal users of them."
In SVN 385, this function fails with a VALUE ERROR:
∇test;⎕io
⎕←⎕io
∇