Failed to use alias command in bash script

Hi,

I'm writing a bash script using alias command. It's normal when I enable alias options with "shopt -s expand_aliases" and put all the code in one file. However, if the script is divided into 2, confusing situation happens.

Below is part of the code to demonstrate the problem. Please help. Thanks.

sub script(sub.sh):

subFunction(){

alias ll="ls -l"

alias -p <= normal here

ll <= command not found

}

main script(main.sh):

source sub.sh

shopt -s expand_aliases

subFunction

ll <= normal here