WORK IN PROGRESS Check back later...
If stdin provided, remaining args are files If no stdin, then first source is special in difference/subtract. Much like lodash
Set progs api
<stdin> | <tool> <args>
Or
<tool> <arg0> <arg1..n>
Map/filter is
<stdin> | <tool> <code>
Or
<tool> <file> <code>
Files are local variables!