[racket] How write regexp for lexer

[Бомбин Валентин]

Hello. I need write rule for lexer for recognize comment which begin from first 
column of line. 
I have next regexp for comment (:seq "//" (:* (:~ CR LF))), aftrer add cr/lf to 
begin of expression i write (:seq  LineTerminator (:* (:or #\space TAB FF)) 
"//" (:* (:~ CR LF))), but this regexp -first eat LineTerninator, second - 
don't recognize comment if it first in file
Help me, please, write this rule
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