[9fans] sam, shorten dot by 1 line

[Rudolf Sykora]

Hello,

having a multiline dot in sam, I wanted to shorten it by one line at
its end. I tried
.,.+0-
which did not work. I had to write
.,.+1-2
or, hopefully equivalently
.,.+-2

While I understand how the latter two ways work, I do not understand
why the first does not.
Can anybody tell me?
Thanks
Ruda

[Rob Pike]

-#0,+#0-2

(go from the null string at the beginning to the null string at the
end of the line starting two lines back from the end.)

-rob

[Rudolf Sykora]

Post by Rob Pike
-#0,+#0-2

This really does not answer the question, neither helps to understand.
Thanks anyway.
Ruda

[Rudolf Sykora]

Post by Rudolf Sykora
.,.+0-

It seems a related question is: why +- behaves differently when I am
somewhere in the middle of a line (the whole line is then a dot) and
when I am at the very beginning of a line (then the *previous* line is
selected)...
Thanks!
Ruda

[Rob Pike]

Break it down:

a,b means: from the beginning of a to the end of b
.,. means: from the beginning of . to the end of .
1 means: from the beginning of line 1 to the end of line 1.
.,.+0 means: from the beginning of . to the end of .+0, and .+0 is the
null string at the end of .

Now the step:

.,.+0-1 means: from the beginning of . to the end of .+0-1, which
means the end of the line preceding the null string at the end of .,
which ends right back at .+0, so it means the last line of ., so this
doesn't work.
.,.+0-2 means: from the beginning of . to the end of .+0-2, which
means the end of the second line preceding .+0, which is one line back
from the end.

QED.

The key observation is that on the right of the comma you're talking
about where the address *ends*.

-rob

[Rudolf Sykora]

Post by Rob Pike
.,.+0 means: from the beginning of . to the end of .+0, and .+0 is the
null string at the end of .

It just does not work for me like that. (.+#0 seems to do what you describe.)

1) Having a line
asdfasdf asdfasdf asdfasdf | asdfasdfa asfdsfasdfa
where | represents the current (emty) dot, .+0 selects everything to
the right from the original dot to the end of the line, including the
newline.

2) Having
| asdfasdf asdfasdf asdfasdf asdfasdfa asfdsfasdf
.+0 does nothing

3) Having
asdfasdf asdfasdf asdfasdf asdfasdfa asfdsfasdf |
.+0 selects the newline, and next .+0 selects the empty dot on the
beginning of the next line, like what we start from in the case 2).

This behaviour, along with the mentioned behaviour of +-, where for
| asdfasdf asdfasdf asdfasdf asdfasdfa asfdsfasdf
+- selects the previous line
while for
asdfasdf asdfasdf asdfasdf | asdfasdfa asfdsfasdfa
it selects the current line
still stays ununderstood by me... (and the last example is contraintuitive).

[sideremark: -+ works even when the empty dot is on the first and last
line of the file, the latter being a problem for +-, which is a
strange asymmetry. How should one then select the line on which a
possibly multiline dot ends and at the same time this is the last line
in the file (which however, you do not have to know if this happens
under some loop command)?]

Any more explanation is highly welcome!
Ruda

[Rudolf Sykora]

Hello 9fans,

could at least somebody comment on the situation I observe?
I.e., what exactly .+0 means, and why the empty dot at a very
beginning of a line (as seen in the editor) seems to actually not be
on the line?

Thanks
Ruda

[Rob Pike]

.+0 goes from the end of the current value of dot to the end of the
line containing dot.
.-0 goes from the beginning of the line containing dot to the
beginning of the current value of dot.

I don't understand your second question.

-rob

[Rudolf Sykora]

Post by Rob Pike
.+0 goes from the end of the current value of dot to the end of the
line containing dot.
.-0 goes from the beginning of the line containing dot to the
beginning of the current value of dot.

Yes, this is what I thought. (But is different from what you initially wrote.)

Post by Rob Pike
I don't understand your second question.
-rob

This pertains to the example I gave:

Having

| asdfasdf asdfasdf asdfasdf asdfasdfa asfdsfasdf

where | represents an empty dot at the beginning of a line (line as
drawn in the editor), .+0 does nothing. According to what .+0 should
do, I'd expect it should select the whole line.

Thanks!
Ruda

[t***@polynum.com]

Post by Rudolf Sykora
Having
| asdfasdf asdfasdf asdfasdf asdfasdfa asfdsfasdf
where | represents an empty dot at the beginning of a line (line as
drawn in the editor), .+0 does nothing. According to what .+0 should
do, I'd expect it should select the whole line.

I'm definitively not an expert, but I always thought that there was only
one legitimate direction of the stream or the string i.e. the direction
of the sequence (addressing lines "3,2" is not legitimate). If this is
handled like a circular buffer, with only one legitimate direction, .+0
goes from the end to the beginning, but in the correct direction in
the circular buffer, and selects nothing (since next to end you have
dot).

Hoping not saying too much nonsense.

[Rob Pike]

Empty dot at the beginning of a line is also empty dot at the end of
the previous line.

I'm not justifying the behavior, just explaining it. This is really
old code with, I admit, some quirky properties. I often think of
rewriting the address code in sam and acme but never do, because a
rewrite would change the behavior of corner cases and break people's
scripts.

Let's move on.

-rob

[Rudolf Sykora]

Post by Rob Pike
Empty dot at the beginning of a line is also empty dot at the end of
the previous line.

This is odd, but one can live with that once they know. Nonetheless,
It should be written somewhere (man page?).

Post by Rob Pike
I'm not justifying the behavior, just explaining it. This is really
old code with, I admit, some quirky properties. I often think of
rewriting the address code in sam and acme but never do, because a
rewrite would change the behavior of corner cases and break people's
scripts.

Still I think things should not stay 'wrong' just because other
scripts have been adjusted to the behaviour. I spent quite some time
finding out why my new script didn't sometimes work. It was kind of
natural to expect that the dot is on the line on which it is drawn to
be.

Ruda