It didn't do what I thought it did with a RevertableProperty; it always
returned Nothing because even if the input properties to <!> are NoInfo, it
casts them to HasInfo.
Even if it had worked, it lost type safety. Better to export the
Property NoInfo that is used in a RevertableProperty, so it can be used
directly.
* Property has been converted to a GADT, and will be Property NoInfo
or Property HasInfo.
This was done to make sure that ensureProperty is only used on
properties that do not have Info.
Transition guide:
- Change all "Property" to "Property NoInfo" or "Property WithInfo"
(The compiler can tell you if you got it wrong!)
- To construct a RevertableProperty, it is useful to use the new
(<!>) operator
- Constructing a list of properties can be problimatic, since
Property NoInto and Property WithInfo are different types and cannot
appear in the same list. To deal with this, "props" has been added,
and can built up a list of properties of different types,
using the same (&) and (!) operators that are used to build
up a host's properties.
Properties now form a tree, instead of the flat list used before.
This simplifies propigation of Info from the Properties used inside a
container to the outer host; the Property that docks the container on the
host can just have as child properties all the inner Properties, and their
Info can then be gathered recursively. (Although in practice it still needs
to be filtered, since not all Info should propigate out of a container.)
Note that there is no change to how Properties are actually satisfied.
Just because a Property lists some child properties, this does not mean
they always have their propertySatisfy actions run. It's still up to the
parent property to run those actions.
That's necessary so that a container's properties can be satisfied inside
it, not outside. It also allows property combinators to
add the combined Properties to their childProperties list, even if,
like onChange, they don't always run the child properties at all.
Testing: I tested that the exact same Info is calculated before and after
this change, for every Host in my config file.
Joey Hess