In Perl RegEx, we have the look-ahead/behind feature; it there a similar functionality available for Wolfram Language patterns?
- Suppose we have a random expression in
FullForm, something like (do forgive me for writing this like lousy json):
H[ <<something>>, l0, h1[ h12[l121], ], h2[ h21, h22[l221, l222] ], h3[ l31, h32[l221, l222] ], <<something>> ]
where I would hope to select (restricted to the first level) all the cases of
Sequence[h1[___],h2[h21,___]] between a
l1 and a
h3[_,h32[__]]. What's the way to do this?