Buffers and commands with optional arguments

["Wolfgang Schuster" <schuster.wolfgang@googlemail.com>]

Hi Hans,

I got yesterday a bug report for my letter module if the \startletter
command takes no arguments.

The following example show the problem without the module.

\def\startletter
  {\dosingleempty\dostartletter}

\def\dostartletter[#1]%
  {\dostartbuffer[letter][startletter][stopletter]}

\starttext

% This did work

\startletter
Text
\stopletter

\getbuffer[letter]

% But this did create a error message from TeX

\startletter

Text

\stopletter

\getbuffer[letter]

\stopletter

One solution for the second text can be solved when I add
a \relax after the \startletter command but I wanted a better
solution.

Because TeX mentions \flushbufferline in error message I tried
to modify the macro and came to the following solution.

%\def\flushbufferline#1%
\long\def\flushbufferline#1%
  {\iftmpblockstarted
     \ifsegmentatebuffer
       \ifemptybufferline
         \immediate\write\tmpblocks{\string\stopbufferparagraph }%
         \immediate\write\tmpblocks{\string\startbufferparagraph}%
       \else
         \immediate\write\tmpblocks{#1}%
       \fi
     \else
       \immediate\write\tmpblocks{#1}%
     \fi
   \else
     \doifsomething{#1}
       {\tmpblockstartedtrue
        %\immediate\write\tmpblocks{\string#1}}%
        \immediate\write\tmpblocks{#1}}%
   \fi}

The macro has to be defined as long and the \string
in the \write command has to be removed. I made a
few short tests and saw no negative sideeffects from
my changes.

Another problem could arise with a few commands
in the letter environment if no empty line is written
after \startletter.

The following result also in a error message.

\startletter
\dorecurse{2}{\input knuth\par}
\stopbuffer

With another modification of \flushbufferline also this
example could work, my final patch was now:

\long\def\flushbufferline#1%
  {\iftmpblockstarted
     \ifsegmentatebuffer
       \ifemptybufferline
         \immediate\write\tmpblocks{\string\stopbufferparagraph }%
         \immediate\write\tmpblocks{\string\startbufferparagraph}%
       \else
         \immediate\write\tmpblocks{#1}%
       \fi
     \else
       \immediate\write\tmpblocks{#1}%
     \fi
   \else
     \convertargument#1\to\ascii
     %\doifsomething{#1}
     \doifsomething\ascii
       {\tmpblockstartedtrue
        %\immediate\write\tmpblocks{\string#1}}%
        %\immediate\write\tmpblocks{#1}}%
        \immediate\write\tmpblocks{\ascii}}%
   \fi}

Could my seond or at least my first patched version
of the \flushbufferline macro integrated into core-buf.mkii
because I won't force users of my letter module to put a \relax
after \startletter only because they use MkII.

Greetings
Wolfgang
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