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Re: [ddlm-group] String concatenation operator in CIF2. .

On Thursday, October 14, 2010 7:48 AM, James Hester wrote:

>There are three separate issues: (1) do we want a string concatenation
>operator? (2) If so, what is the grammar for this operator (3) what
>character(s) will be used for this operator?


>Regarding the particular characters to use to represent concatenation:
>'+' is a poor choice given its possible uses as a datavalue in its own
>right, and I find that  '_' is a little unintuitive and unnecessarily
>overloads underscore. Note that there is no reason to limit ourselves
>to a single character as we expect this operator to be used very
>sparingly: we can use a digraph or trigraph if we so desire,
>especially if it makes the meaning clearer to a naive user.

If a concatenation operator is adopted, then I agree with Simon that it should be something that is not legal as a whitespace-delimited data value.  (Ideally, not in CIF1, either.)  I would prefer that it not be legal even as the leading character(s) of a whitespace-delimited data value.  Without departing from the allowed ASCII characters, the lone underscore is the only viable string I see that meets all those criteria.

I don't so much mind '//' as a concatenation operator, except that it must then be made a reserved word, and maybe even a reserved prefix.  At least such a reservation is less likely to be a problem than reservation of '+' would be, but I don't see that choice as much more intuitive to the average user than '_'.


John C. Bollinger, Ph.D.
Department of Structural Biology
St. Jude Children's Research Hospital

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