kocircuit clarify the use of `ko play`

I followed the starting instructions, but "ko play" doesn't seem to want to play with me.

% ko play github.com/kocircuit/kocircuit/codelab/HelloWorld
(/home/rog/src/go/src/kocircuit/kocircuit/lang/go/sys/compile.go:31) (ko/R0) compiled functions=0 steps=0 steps-per-function=0.00
cannot find main circuit github.com/kocircuit/kocircuit/codelab/HelloWorld

It is not clear what the correct argument to "ko play" should be. The go play help doesn't document its positional arguments.

Sep 25 '18 19:09 rogpeppe

@rogpeppe Are you using multiple GOPATHs (e.g. /home/u/goget:/home/u/Desktop/go)? If so, see https://github.com/kocircuit/kocircuit/issues/5#issuecomment-424447383

Sep 25 '18 19:09 mewmew

I am not. I'm using Go 1.11.

Sep 25 '18 20:09 rogpeppe

@rogpeppe Did you do a go get already? See https://github.com/kocircuit/kocircuit/blob/master/lessons/0-intro/1-setup.md

Sep 27 '18 06:09 ewoutp

I think the issue was that I didn't have the kocircuit source installed in my $GOPATH (GOPATH is going away and I was using modules).

All the same, the output of ko help play does not mention that it takes any command line arguments at all, let alone what they're expected to be or how they are interpreted. This should probably be fixed.

Sep 27 '18 11:09 rogpeppe