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Re^6: Turing completeness and regular expressions

by JadeNB (Chaplain)
on Nov 28, 2009 at 18:34 UTC ( #809929=note: print w/ replies, xml ) Need Help??


in reply to Re^5: Turing completeness and regular expressions
in thread Turing completeness and regular expressions

Thanks for clarifying—I think that I do take your meaning correctly now.

My issue comes with one subtle point, which is that, as you mention, we have a choice between incorporating a look-up table into our string, or using multiple substitutions; and the most naïve way of making use of the look-up table, as I did, turns the substitutions from s/fixed/fixed/ to something involving capturing parentheses. My question was thus: Can we get the best (or “apparently least computationally powerful”) of both worlds, by having just one substitution, but not using anything but the ordinary (theoretical-CS, not Perl-enhanced) regular-expression constructs—in particular, no back-references—in it?


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