Translating from LaTeX to ConTeXt: environments

["Giuseppe Bilotta" <oblomov@freemail.it>]

As I already said in a previous post, I'm trying to convert some LaTeX files
to ConTeXt. The next problem I'm facing is:

What's the ConTeXt equivalent of a (generic) LaTeX environment? To be
precise, I'm looking for an equivalent of the "verse" LaTeX environment. I
would assume that  and appropriate \defineparagraphs (with n=1) is the
answer. The problem is to set the paragraphs appropriately: I need to nest a
\startnarrower ... \stopnarrower (to ensure narrower margins) and a
\startlines ... \stoplines. But it does not seem to work:

\def\SongStart{\startnarrower[2*left,right]\startlines}
\def\SongStop{\stoplines\stopnarrowe}
\defineparagraphs[song][n=1]
\setupparagraphs[song][style=italic,before=\SongStart,after=\SongStop]

gives an incomplete conditional error (the same also swapping narrower and
lines).
Does anybody know a solution?

One more question: is there an easy way to define a command (\def) that
accepts an optional parameter? I mean:

\command{argument}

does one thing,

\command[optional]{argument}

does another, depending on [optional]. (btw, Hans, this is what I meant when
asking for a "programmer's reference").

Giuseppe Bilotta