问题
I'm trying to write a regular expression to validate moves in algebraic chess notation. Here's what I have so far:
/
O-O(-O)? # Castling
|[KQRBN]x?[a-h][1-8]\+? # Most normal moves and captures
/
Where I am lost is pawn promotion.
A knight, bishop, or centre pawn may only promote on the file from which it starts or the file on either side via a capture. A rook pawn may promote by moving straight or capturing to one side, depending on whether it is on the a- or h- files. So something like
/[a-h](x[a-h])?[18]=[QRBN]\+?/
doesn't work, because fxh8 is not a valid move (only fxe8 and fxg8 are). I could go the long route with
/(a(xb)?|h(xg)?|b(x[ac])?.../ # insert 5 more files in place of the ...
but that's not very efficient. I want to use grouping, so that I can do rook-pawns, and everything else. I have something like this in mind:
/([b-g])(x(\1±1))?/
To indicate "the letters b to g may be followed by the letter that comes before or after them".
回答1:
Matching the adjacent letter is not hard using alternations, but you won't find anything compact as there is no character arithmetic in regex.
Someone just posted a similar question out of sympathy for your plight.
The long way is the only way.
来源：https://stackoverflow.com/questions/24344875/regex-to-match-something-based-on-what-was-matched-before