I'm really intrigued by the concept of array Shapes. I actually implemented that for Obvious and use it for type checking hashes in ruby with Contracts. https:/

I'm really intrigued by the concept of array Shapes. I actually implemented that for Obvious and use it for type checking hashes in ruby with Contracts. https://github.com/RetroMocha/obvious/blob/master/lib/obvious/contract.rb#L176 https://github.com/RetroMocha/obvious/blob/master/lib/obviou... It's cool to see the same idea implemented in Hack. I don't know if anyone at FB has even heard of Obvious, but it's cool that they had the same idea in their language.