How do I apply a hackage mirror?

[glyh]

The connection to hackage is bad in my region. So I need to figure out how to configure a hackage mirror. I have successfully configure it for either stack or cabal as there's tons of tutorial out there. But I can't figure out how to do it with haskell.nix.

There's #1293, but it only overrides a single package source.

Also, it looks like https://input-output-hk.github.io/haskell.nix/reference/modules.html#packagessrc is the way to go, but I am new to nix and I couldn't figure out how to override that. Could you please provide a simple example for it?

Thanks.