update

doc/todo/info_propigation_out_of_nested_properties.mdwn

@@ -12,6 +12,7 @@ This works, but it's error-prone. Consider this example:
 Here, the Info of `foo` is not propigated out. Nor is `bar`'s Info. Of
 course, only one of them will be run, and only its info should be
 propigated out..
+
 ----
 
 Currently, ensureProperty detects if it's called on a property with a
@@ -73,8 +74,7 @@ that has no Info. Only allow calling ensureProperty on this new type.
 (Or, remove propertyInfo from Property, and add a new InfoProperty that
 has the info.)
 
-This would surely work, but it adds a lot of complexity to property
-combiators. Also, propertyList could only contain one type at a time,
+But, propertyList can only contain one type at a time,
 not a mixed list of Property and SimpleProperty.
 
 Could a GADT be used instead?
@@ -85,9 +85,21 @@ Could a GADT be used instead?
 	data HasInfo
 	data NoInfo
 
-	data Property i where
-	        InfoProperty :: Desc -> Propellor Result -> Info -> Property HasInfo
-	        SimpleProperty :: Desc -> Propellor Result -> Property NoInfo
+	data Property = IProperty (GProperty HasInfo) | SProperty (GProperty NoInfo)
 
-	ensureProperty :: Property NoInfo -> Propellor Result
-	ensureProperty (SimpleProperty d r) = r
+	data GProperty i where
+		GIProperty :: Desc -> Propellor Result -> Info -> GProperty HasInfo
+		GSProperty :: Desc -> Propellor Result -> GProperty NoInfo
+
+	ensureProperty :: GProperty NoInfo -> Propellor Result
+	ensureProperty (GSProperty d r) = r
+
+That works. I made a `gadtwip` git branch that elaborated on that, 
+to the point that Property.File compiles, but is otherwise 
+unfinished. Most definitions of `Property` need to be changed to
+`GProperty NoInfo`, so that ensureProperty can call them. It's a big,
+intrusive change, and it may complicate propellor too much. 
+
+(I may need to make instances of Prop for `GProperty NoInfo` and `GProperty
+HasInfo`, if that's possible, and make more Property combinators work on
+Prop.)