Since expat v1.0 it’s now possible to use guards on your pattern definitions, and they will be expanded at the call-site.
Whoo! This now entirely replaces my purposefully gimped (since it was a standards suggestion and not a real library) library of defguard. ^.^
Although I think I still like the syntax of mine better, I just think that it should be built into elixir instead of the highly gimped-in-comparison defguard that it recently got (though it could be expanded in the future…)
I like how you encourage your’s as a constructor too, do the guards apply on that properly? 
