Re: RS/RE and paragraphing macros

[Alex Colomar]

Hi Branden,

On 2/21/23 01:29, G. Branden Robinson wrote:
> At 2023-02-21T00:46:11+0100, Alex Colomar wrote:
> > On 2/21/23 00:30, Alex Colomar wrote:
> > > Hummm, this is definitely not as simple as "breaks the line and moves
> > > the margin".  The margin is not moved because of 0, so this should be
> > > just equivalent to .br from your own definition.  However, it's not.  It
> > > does some extra magic, which I'd call "RS sets the indentation of the
> > > scoped block to 0; RE resets to the previous indentation".
> >
> > That's not even completely true.  Let's try something more precise.
> >
> > RS breaks the line, moves the left margin by a relative inset, and sets the
> > indentation to 0.
>
> Close.
>
> .\" Start a relative inset level (by the amount given in the argument).
> .\" .RS [indent]

Which reminds us that this was missing in your recent patch, right? :)

> .de1 RS
> .  nr an-saved-margin\\n[an-inset-level] \\n[an-margin]
> .  nr an-saved-prevailing-indent\\n[an-inset-level] \
>       \\n[an-prevailing-indent]
> .  ie \\n[.$] .nr an-margin +(n;\\$1)
> .  el         .nr an-margin +\\n[an-prevailing-indent]
> .  in \\n[an-margin]u
> .  nr an-prevailing-indent \\n[IN]
> .  nr an-inset-level +1
> ..
>
> RS (1) saves the previous margin setting and "prevailing indent" (this
> term goes all the way back to McIlroy's 1979 man(7)); (2) insets (moves
> right) the margin by the amount in the argument, or by the
> aforementioned prevailing indent if there is no argument; (3) sets the
> formatter's indentation to this new value (not "0"); (4) updates the
> prevailing indent by the user-configurable standard indentation
> (register `IN`); and (5) increments the inset level.

This confuses me again.  All the references to indentation mean the 
inset-amount, right?  What happens to the actual indentation (as in IP)?

> > RE breaks the line, resets the left margin to the previous value, and
> > resets the default indentation of indented paragraphs to the one
> > previous to RS (so if the next paragraph is IP, it will continue with
> > the old indentation).
>
> It does a lot of error checking first.
>
> .\" End relative inset level, backing up by one level (or to the level
> .\" given by the argument).
> .\" .RE [inset-level]
> .de1 RE
> .  ie \\n[.$] .nr an-RE-requested-level \\$1
> .  el         .nr an-RE-requested-level (\\n[an-inset-level] - 1)
> .  ie \\n[.$] \{\
> .    if (\\n[an-RE-requested-level] = \\n[an-inset-level]) \
> .      ds an-RE-problem already at level \\n[an-inset-level]\"
> .    if (\\n[an-RE-requested-level] > \\n[an-inset-level]) \
> .      ds an-RE-problem too large\"
> .    if (\\n[an-RE-requested-level] < 1) \
> .      ds an-RE-problem too small\"
> .    if d an-RE-problem \
> .      an-style-warn argument """\\$1""" to .\\$0 \\*[an-RE-problem]
> .    rm an-RE-problem
> .  \}
> .  el .if !(\\n[an-RE-requested-level]) .an-style-warn unbalanced .\\$0
> .  rr an-RE-requested-level
>
> ...and with that out of the way, we get to an implementation fairly
> symmetric with RS.
>
> .  ie \\n[.$] .nr an-inset-level ((;\\$1) <? \\n[an-inset-level])
> .  el         .nr an-inset-level -1
> .  nr an-inset-level (1 >? \\n[an-inset-level])
> .  nr an-margin \\n[an-saved-margin\\n[an-inset-level]]
> .  nr an-prevailing-indent \
>       \\n[an-saved-prevailing-indent\\n[an-inset-level]]
> .  in \\n[an-margin]u
> ..
>
> Essentially it "pops" the prevailing indent and margin that `RS` pushed,
> permitting multiple pops at once.
>
> > I'm not sure how to word it better.
>
> What I quoted in my previous message in the best I've been able to do.

Let's try to improve that then.  I'm still not convinced ;)

> You will note that neither macro _explicitly_ breaks.  That is because
> the `in` request causes a break (when invoked with the regular control
> character).  And both macros _always_ invoke `in`, barring usage errors.
>
> Regards,
> Branden

Cheers,

Alex

--
<http://www.alejandro-colomar.es/>
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