That looks like Haskell source code. Well, maybe some similar language. If that's indeed Haskell, then those words that start with a capital letter are "data

That looks like Haskell source code. Well, maybe some similar language. If that's indeed Haskell, then those words that start with a capital letter are "data constructors". Well, think a decent language will usually have one or two data constructors: cons for lists and something to make arrays. But, in Haskell, for some reason... they allow you to define your own. Functionally, the thing is a preparation for the follow-up code that matches some data bits to one of these "classes" and executes some bits of code if the "class" matched.