Smalltalk defines an anonymous function expression (a "block") as an instance of its library's BlockContext class.
Depending on the constructs available in the core language, a standard library may include: Commonly provided functionality includes: Philosophies of standard library design vary widely.
One ideal is for a programmer to be able to find every interesting, significant, and reasonably general class, function, template, etc., in a library.
[1]This suggests a relatively small standard library, containing only the constructs that "every programmer" might reasonably require when building a large collection of software.
By contrast, Guido van Rossum, designer of Python, has embraced a much more inclusive vision of the standard library.