It only shows "correct" code and never has a syntax error or lets you try out yo...

sp332 on Aug 22, 2014 | parent | context | favorite | on: Silent Teacher – A game to learn how to code

It only shows "correct" code and never has a syntax error or lets you try out your '42' - '2' example. It starts with bare numbers without the word "var" and later adds the word "var" with no explanation.