###Make |, & and ^ built-ins do something useful on blocks###

E.g. `<array/string> <block> |` can be used as index function

    [0 -10 -20 30 40 -50 60] {0<} |   # -> [1 2 5]

Any ideas for `<array/string> <block> &` or `<array/string> <block> ^`?