Are there any good (or at least interesting but flawed) analogs to regular expressions in two dimensions?
In one dimension I can write something like /aaac?(bc)*b?aaa/ to quickly pull out a region of alternating bs and cs with a border of at least three as. Perhaps as importantly, I can come back a month later and see at a glance what it’s looking for.
I’m finding myself writing custom code for analogous problems in 2d (some much more complicated / constrained) and it would be nice to have a more concise and standardized notation, even if I have to write the engine behind it myself.
A second example might be called ‘find the +’. The goal is to locate a column of 3 or more as, a b bracketed by 3 or more as with three or more as below. It should match:
..7...hkj.k f 7...a h o j ----a-------- j .a,g- 8 9 .aaabaaaaa7 j k .a,,g- h j hh a----? j a hjg and might be written as [b^(a{3})v(a{3})>(a{3})<(a{3})] or…
Suggestions?
Not being a regex expert, but finding the problem interesting, I looked around and found this interesting blog entry. Especially the syntax used there for defining the 2D regex looks appealing. The paper linked there might tell you more than me.
Update from comment: Here is the link to the primary author’s page where you can download the linked paper ‘Two-dimensional languages’: http://www.mat.uniroma2.it/~giammarr/Research/pubbl.html