That should be 
s/(\w+)(?(?{ !$d{$1} })(?!))/$d{$1}->($1)/ge;

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Your solution fails if the non-existant word is followed by a one ("1"). For example, try input "baz1".

In reply to Re^2: Check exist of anonymous subroutine before calling it within regexp substitute? by ikegami
in thread Check exist of anonymous subroutine before calling it within regexp substitute? by jffry

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