Local accumulators for cleaner comprehensions

Phew.. Glad you’re not going to take (me) away the <~ operator :slight_smile:

One question @josevalim: Will these local accumulators work within cond? I sometimes miss this feature to have the a variable set in an above condition and then reused below. Sure we can use with instead, but cond’s are far cleaner and more readable then with true <- something || something_else.