1. 命令式语言(imperative)和函数式(funcional)语言
2. 静态类型语言和动态类型语言，取决于类型检查时在编译器还是运行期，比如：Python一个符号可以不指定类型，只是一个名字，在运行时可以随意帮上任何类型，然后用这个名字去访问它。
3. 动态语言的缺点，因为缺乏类型，编译器无法检查语法错误，使得程序出错的可能增加，debug困难，比如：在函数中用错了一个名字，Python认为这是一个新定义的名字，不会报语法错误
4. "First-class" Type,一般是针对函数是不是可以作为函数的参数，实例化。
5. Functions are actually a special case of closures: blocks of code that can be called later. The code in a closure has access to things like variables and functions that were available in the scope where the closure was created, even if the closure is in a different scope when it is executed—you saw an example of this already with nested functions. You can write a closure without a name by surrounding code with braces ({}). Use in to separate the arguments and return type from the body