Module test.eff.valid.nested.

Rule leaf_http, produce. It performs io [Http]:
  Return Http.get("/health").

Rule mid_io, produce. It performs io [Http, Sql]:
  Let resp be leaf_http().
  Return Db.insert("logs", resp).

Rule root_io, produce. It performs io [Http, Sql, Time]:
  Let data be mid_io().
  Let ts be Time.now().
  Return (ts plus ": ") plus data.