Another way to think about it is kinda related to pg's stratified design. At the lowest level, you have things like system services, files, sockets, perhaps oth

Another way to think about it is kinda related to pg's stratified design. At the lowest level, you have things like system services, files, sockets, perhaps other processes. Regular old code may use those abstractions - or not - and build new stuff. for example parsers, matrixes, http responses, database connections. Just like regular old code helps you manage the relationships between an input file and an output file, the type system helps you manage the relationship between libraries, or sets of functionality in your code. I don't care what type of data you pull from the database, but that type must agree with the type of matrix you're constructing. The parser may return a syntactically correct tree, or an error. One use of the type system is to ensure that all possible error conditions are handled in a meaningful way. You can do this in java, but haskell's type system is a bit more expressive, so it's easier to enforce higher level constraints. Another way to look at it, the type system is like the algebra axioms you want your system to follow. if equality is reflexive, a == b, then also b == a. At that level we don't care if a is 5 or "hello" or @TcpConnection(0x1342341a).