Value patterns: do vs. collect

Questions
#1

Hi all, I just encountered something that has me puzzled. I’m aware that you can use .collect on a pattern to modify its output:

p = Pwhite(1, 9).collect(_.squared).asStream.nextN(10);

And I had assumed that .do would behave similarly, except that it would return its unmodified receiver, instead of a modified result. However, the following seems to crash the interpreter, and I see nothing in the post window.

p = Pwhite(1, 9).do(_.squared).asStream.nextN(10);

Does anyone know what I’m overlooking or misunderstanding?

Eli

#2

With Pwhite(1, 9).do(...) you make an infinite loop. It doesn’t crash the interpreter but locks it up.

Unlike collect(), do is not “lazy”. (collect called on a pattern returns a new pattern Pcollect, but do really tries to run over all the elements in the Pwhite).

#3

Makes perfect sense, thanks. I did not realize one was lazy and the other wasn’t!