Parse::RecDescent grammar:

my $grammar = <<'__EOI__'

    {
        use strict;
        use warnings;
    }

    parse    : list /\Z/ { $item[1] }
    list     : '(' list_ele(s?) ')' { $item[2] }
    list_ele : list | TERM
    TERM     : /\w+/

__EOI__
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