Using your framework, I got f() down to 97.

($a=join"|",a..z)=~s/join"|",@{pop@_}//eg;($g=shift)=~s!_![$a]!g;/^$g$
+/&&push@m,$_ for@{pop@_};@m
[download]

If I could change the order of the arguments, I could cut 2 characters by make the shift a pop. I am a little perplexed as to why @{pop@_} won't let me do a @$_[0], which would cut another 3 characters. *shrugs*

Update: I feel slightly inadequate after reading japhy's contributions. *sighs*

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We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.