Set acl in haproxy based on client ip using map_ip

Question

In haproxy configs, I need to be able to look up the client ip of a request in a map of IP cidrs and then set an acl if the client ip exists in the map

We can assume that I have a map <path_to_map/ipcidrs.map> which is populated like this:

1.12.123.12/24  1.12.123.12/24

We can also assume that i have a txn variable that gives us the IP txn.ip

I've tried this:

acl is_IP_in_map var(txn.ip),map_ip(<path_to_map>/ipcidrs.map)

I noticed that the acl was not being set.

Is there something that i am missing here? Can anyone suggest alternatives?

Things to consider:

1. I'm aware that I can use a list, but I think I need to use a map because the map is being dynamically updated via the runtime client(updateMap). Im assuming that list updates are more expensive that map updates. Hence the choice for maps.
2. the ipcidrs.map contains cidrs. Hence the need for map_ip. Simple string matching could have worked were the map filled with IPs.
3. Yes, the value in the map is redundant. but this is based on point 1 where i need to key off the client IP based on the cidr value.