It you're going to allow (a+b)' — the OP might be happy with only supporting /\w+'/ — you must allow (a*(b+c))' too.
Other than that, there are a few other problems.
You don't handle xor, you assume the same precedence and associativity as Perl, and you don't generate a truth table. I presume that's intentional and that you're leaving those as an exercise to the reader, so I'm just documenting what's left to do.
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