For example:
send_fp = default_send;
if ("converting from macro-html to html") # use internal conversion
send_fp = send_macro_html;
if ("converting from xyz to html") # uses external conversion
open(stdout, "|xyz2html"); # this is perl, but you get the idea
...
(*send_fp)(stdin, stdout);
Of course, it'll need to be more robust (e.g., you wouldn't use two internal
conversions unless you wrote a streams object to move the data around).
However, if you just setup pipe()'s and fork() you can easily use muliple
internal conversions (that just read stdin and write stdout) and the system
will handle the streams for you. This is efficient enough for most systems,
esp on systems with copy-on-write. This is how Plexus handles it.
+--+
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