I develop wordpress theme using roots theme framework and I usually use Bootstrap glyphicon like this:
.icon-mobile-application {
    .glyphicon;
    .glyphicon-asterisk;
}
Now I want to use font-awesome in similar way so I include font-awesome.less in my app.less and wrap it in my own css rule like this:
.icon-web-development {
    .@{fa-css-prefix};
    .@{fa-css-prefix}-code;
}
But when I try to compile it return error:
>> Parser error in app.less
>>       93.     .icon-web-development {
>>       94.         .@{fa-css-prefix};
>>       95.         .@{fa-css-prefix}-code;
Warning:  Use --force to continue.
I also try:
.icon-web-development {
    .fa;
    .fa-code;
}
Showing error: Fatal error: .fa is undefined. What am I missing here?