Docs: lazy evaluation

[andrewbaxter]

I need to stream lines from a command that runs forever and run code for each line. Naive interpretation of the docs would imply that the since for takes a single value, the evaluation of the value completes before the for begins to execute so trying this with a for loop wouldn't work.

It's ambiguous whether this would work with each, and the documentation for output capture doesn't explicitly state this either. In most languages with first class functions I try to avoid first class functions for simple control flow like this because it messes with other control flow operators, so I was hoping I could use for.

FWIW I searched for variations of "stream" but that only came up with references to "byte streams", "lazy", a few other things (can't remember what) as well as checking the for, each, section on lists vs multiple values, output capture, and command evaluation.