! http://www.reddit.com/r/programming/comments/7pg5b/an_rpn_calculator_in_46_languages_and_growing/c070ns9 USING: continuations eval io kernel prettyprint sequences ; IN: rpn : rpn ( -- ) [ readln "USE: math " prepend [ eval ] [ "Please enter a valid expression." ] recover pprint nl t ] loop ; MAIN: rpn