[[!comment format=mdwn
 username="joey"
 subject="""comment 1"""
 date="2017-08-25T23:07:12Z"
 content="""
It's not allowed for the content of Info to come from an IO action.
Info has to be static. This allows one Host to introspect the Info of
another Host. The Dns properties rely on that.

So, the type checker is right in preventing this. It's also not allowed
to use ensureProperty with a property that HasInfo, as the info would
not propigate to the outer property. The type checker is also preventing
you making that mistake.

(You also forgot to pass the `w` parameter to `ensureProperty`, 
which made the type checker unhappy as well and probably confused the error
messages.)

To accomplish your goal, you could use:

	data DebOMaticHostMirror = DebOMaticHostMirror

If a Host has this in its Info, you know that Host is the one with
debomatic installed. You can then get its hostname using the `hostName`
field accessor on the Host. 

The property that does that will need to be passed a `[Host]` which will
typically be the `hosts` list defined in config.hs.
"""]]
