On Sun, 12 Aug 2018, Rik Kabel wrote:
%% How can one remove blank lines at the start of a buffer so that
%% commands that grab a buffer can be used in the same way as, for
%% example, \startparagraph...\stopparagraph, which allow blank
%% lines around the content?
%%
%% The problem appears when an optional argument is allowed but none
%% is provided. Adding \relax does not help; adding empty brackets
%% does. I see no way to distinguish between a buffer without
%% leading blank lines and a buffer that was created when brackets
%% are provided.
%%
%% \inlinebuffer handles the leading blank lines when there is
%% nothing prepended, but I need to prepend. (It also handles the
%% unwanted trailing line, but that is not an issue here).
%%
%% How can I unpack the buffer, apply the equivalent functions of
%% ignorespaspaces and removeunwantedspaces to it, and repack it?
%% The buffer may contain internal blank lines and macros, and
%% those should be retained. Or, is there already a function to
%% strip a buffer in the manner that string.strip does a string?
\setupwhitespace[none]
\setupindenting[none]
\define\Mark{\color[middlegray]{\itb¿\ }}
\define\First{nothing yet}
\define\Arg{nothing yet}
\setuplanguage[en][spacing=packed]
\starttexdefinition unexpanded startBufTest
\bgroup
\dosingleempty\dostartBufTest
\stoptexdefinition
\starttexdefinition dostartBufTest [#SETUPS]
\doifsomethingelse{#{SETUPS}}
{\define\Arg{yes}}
{\define\Arg{no}}
\iffirstargument
\define\First{yes}
\else
\define\First{no}
\fi
\relax
\getrawparameters[BufTest][xx=yy,#SETUPS]
\grabbufferdata[TestBuffer][startBufTest][stopBufTest]
\stoptexdefinition
\starttexdefinition stopBufTest
\startparagraph
\dontleavehmode\llap{\Mark}\inlinebuffer[TestBuffer]
\ (first: \First, arg: \Arg)
\stopparagraph
\egroup
\stoptexdefinition
\starttext
\startparagraph
A starting paragraph.
\stopparagraph
\startBufTest
Buffer without blank lines.
\stopBufTest
\startparagraph
An intervening paragraph.
\stopparagraph
\startBufTest
Buffer with blank lines.
\stopBufTest
\startparagraph
An intervening paragraph.
\stopparagraph
\startBufTest\relax
Buffer with \tex{relax}.
\stopBufTest
\startparagraph
An intervening paragraph.
\stopparagraph
\startBufTest[]
Buffer with \type{[]}.
\stopBufTest
\startparagraph
An intervening paragraph.
\stopparagraph
\startBufTest[key=value]
Buffer with \type{[key=value]}.
\stopBufTest
\startparagraph
A closing paragraph.
\stopparagraph
\stoptext
\stopmode
Perhaps \ignorespaces might work, but I often find that the conceptually
simplest solution is to post-process the buffer at the lua end. See
http://wiki.contextgarden.net/Programming_in_LuaTeX#Manipulating_verbatim_text
for an example.
Aditya
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