[[!comment format=mdwn username="joey" subject="""comment 1""" date="2016-09-20T15:14:19Z" content=""" The compiler error message here is not nice; if [[todo/use_ghc_8.0_custom_compile_errors]] is able to be implemented some time, I'd hope for a error message more like: Couldn't match Property DebianLike with UncheckedProperty UnixLike Perhaps you forgot to use `changesFile` or `assume MadeChange`? Instead of the current mess which has a lot of bloat from type families. The meat of the error is here: src/Propellor/Property/SiteSpecific/Pebble.hs:29:5: Couldn't match type ‘Propellor.PropAccum.GetMetaTypes (CombinedType (UncheckedProperty UnixLike) (Property UnixLike))’ with ‘Propellor.Types.Singletons.Sing y0’ The type variable ‘y0’ is ambiguous Expected type: Propellor.PropAccum.GetMetaTypes (CombinedType (UncheckedProperty UnixLike) (Property UnixLike)) Actual type: Propellor.Types.MetaTypes.MetaTypes y0 cmdProperty has type UncheckedProperty UnixLike; in order to get a Property that runs a command, you have to provide some way of checking if the command made a change to the system. Since running tar certianly changes the system, adding `assume MadeChange` after it should do. Running pip install may not alwways change the system; it's up to you if you want to do a real check for change there or again `assume MadeChange`. I think those two changes are all you'll need to get it to compile. """]]