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[Groff] Re: problem with pic


From: Brian Kernighan
Subject: [Groff] Re: problem with pic
Date: Sat, 22 Mar 2008 05:56:47 -0400 (EDT)
User-agent: Alpine 1.00 (GSO 882 2007-12-20)

Werner, et al --

It's been a long time, but this one I do remember -- the intent
of "then" in such constructs is definitely to separate components
of a path, and that phrase appears in several documents that I
have still lying around, including the paper in SP&E and one
that seems to have meant for some ACM SIG.

This may be an instance of something I added that wasn't carried
over into the development organization that distributed "official"
source.

Brian

On Sat, 22 Mar 2008, Werner LEMBERG wrote:


I suppose it is going to boil down to a matter of "taste".

Old AT&T pic treated

  line from 1,1 then up 1

exactly the same as

  line from 1,1 up 1

As I read pic documentation, these *should* behave differently; the
former should plot two line segments, the latter only one.  If AT&T
pic produces identical results in both cases, then IMO it doesn't
behave as documented, so could be considered broken.

Yes, AT&T is broken here, I think.  In CSTR 116, section 8 (`Lines and
Splines'), it is explicitly written:

 The word `then' separates components of the path.

And examples are given like that:

 line right 1 then down .5 left 1 then right 1

which makes a zig-zag line having three components.  So it is clear
that `components' are visible parts of the line, not syntactical
parts.  However, examples using the `from' keyword are given only for
arcs, so I assume that during development of pic this particular case
slipped through the grammar.

Brian, could you comment, please?


   Werner

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