Proper regex to prevent a match when keyword is preceded by a period

Question

I'm writing a color syntax highlighting file for a derivative of Pick Basic. Two of the oddities that this language allows is periods in variable names and embedding a keyword in a variable name, surrounding by periods. So for example, AND is a keyword, but FOO.AND.BAR is a variable name. I'd like to prevent the AND in the middle of a variable name from being highlighted, but my attempts are failing.

I've defined my set of keywords as contained, but the container definition isn't working, and I'm not quite sure why.

Two different attempts (different keyword sets, but the same basic idea). The only difference in these two examples is that some builtin language functions contain periods (and thus need to be in the middle character class), while operators do not.

syn keyword universeBasicFunctionName  ABORTM ABS ABSS ACOS ADDS ALL ALPHA AM ANDS ARG. ASCII ASIN ASSIGN ASSIGNED ATAN AUTHORIZATION contained
syn match universeBasicFunction /\M\( \)\@<=\zs[A-Z\.]\+\ze\([ (]\)\@=/ contains=universeBasicFunctionName
syn keyword universeBasicOperatorName      AND EQ GT LT MATCH MATCHES NE NOT OFF ON OR contained
syn match universeBasicOperator /\(\.\)@<![A-Z]\+\(\.\)@!/ contains=universeBasicOperatorName

Answer 1

You basically want to have the . be considered part of syntax keywords, so that AND won't be matched by the Keyword FOO.AND.BAR.

The proper way to configure this for syntax rules is to make use of the :syn iskeyword setting, in your case, to just add the . to it, simply put (at the top of your syntax rule):

syn iskeyword @,48-57,_,192-255,.

This uses the default 'iskeyword' setting (and adds the . at the end to it).

The syn-iskeyword command, only affects what is considered a keyword by the syntax engine (e.g. only for syn keyword foobar FOO BAR FOOBAR), it does not change anything related to actual matching using e.g. :syn match or :syn region commands).

I obtained the default for the syn-iskeyword option, by quering the 'iskeyword' option value using e.g. :echo &isk.

Note: Both settings are closely related (and in fact in older Vims, there did not exist the :syn iskeyword feature).

For syntax rules however, you should always use :syn iskeyword simply because the option 'iskeyword' affects a whole lot of other (possibly unrelated) things, like word movement and other Vim commands. And for that reason, the :syn iskeyword command was added later on, to de-couple setting this for syntax highlighting (in 7.4.1142)