[Haskell-cafe] Building ? using kleene closure {not haskell specific}

[C K Kashyap]

Hello gentle Haskell folks,

I happened to read "Beautiful code"'s chapter 1 today and found Brian
Kerninghan's regex implementation. In it he only shows the * meta character.
I can easily understand how + can be built but am having trouble with
building ? (zero or one). I'd really appreciate it if some one could help me
understand it.

Regards,
Kashyap
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