Dyalog also deviates from the ISO standard, adding things from J like hooks and forks. IIRC, GNU APL's deviations are to bring it closer to IBM APL2, but it's b

Dyalog also deviates from the ISO standard, adding things from J like hooks and forks. IIRC, GNU APL's deviations are to bring it closer to IBM APL2, but it's been a while since I cared about any of this.