issue in irule and data group list

version is 11.0

I follow the "ltm_concepts_guide_v11_0" and try to test the data group list.

the sample is as below

when CLIENT_ACCEPTED {
if {[matchclass [IP::remote_addr] equals $::aol]}{
pool tw_proxy_slb_pool
  }
}

And i add my client subnet in default data group file "aol"

the test result is fail.

the error message is as below

TCL error: /Common/test_data_group - can't read "::aol": no such variable while executing "matchclass [IP::remote_addr] equals $::aol"

any idea?