Strings vs expressions

James Bonfield jkb at
Mon Feb 19 15:43:08 UTC 2001

Hello all,

When is a expression within a string a real expression, and when is it just
part of the string?

Clearly not all $ symbols in strings form expressions. Eg dbiblast.acd
contains a string:

	pattern: "^([0-9]+.[0-9]+.[0-9]+)?$" 

Mostly complex expressions are wrapped in @(), but not always. Eg see

	def: $(sequence.begin)-$(sequence.end)

How can I tell expressions from just internal dollars. There doesn't appear to 
be any escaping syntax, which means this _must_ be clearly defined to avoid
bugs. My current ruling is if isn't followed by ( then it's not an
expression. Is that valid?


James Bonfield (jkb at   Tel: 01223 402499   Fax: 01223 213556
Medical Research Council - Laboratory of Molecular Biology,
Hills Road, Cambridge, CB2 2QH, England.
Also see Staden Package WWW site at

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