Pipelines

Use Case: mean monday (t-aggregation)

   Nfork   { lambda => t.weekday }        # classify
 | Ngrep   { lambda => t.weekday = Mon }  # filter
 | Nreduce { lambda => mean }             # aggregate

pipeline operators: | & ()
primitive TS operators:
-- Nfork, Njoin, Nmap, Nreduce, Null, Tfork, Tjoin, ....
purely functional language
-- allows for global optimization, distribution