/ simple reverse polish notation interpreter
/ http://www.stacken.kth.se/~foo/rpn/

p:{(. 1_)'(&x=" ")_ x:" ",x}		/ parse
e:{:[7=4:y;(-2_ x),y .-2#x;x,y]}	/ evaluate
s:();.m.r:{`0:,5:s::s e/p x}		/ read-eval-print loop