my $base_class = '...'; # base class for exceptions
my $error_class = '...'; # my error class

sub fixerror(;$) {
    my $e = @_ ? $_[0] : $@;

    return $e
        if blessed( $e ) && $e->isa( $base_class );

    return $error_class->new( $e );
}

sub try(&) {
    my $code = $_[0];

    eval { &$code() };

    $@ ? fixerror($@) : undef;
}