Programming language terminology lesson: Closures

In reading Beyond Java by Bruce Tate, I saw the following:

Java’s syntax lacks features like closures and code blocks (which let you pass a block of code as an argument).


In the vast majority of languages that support them, a block is a closure! Blocks, closures, lambdas — they’re all just different words for the same thing! A closure is just a piece of code that carries around (“closes over”) definitions from the environment in it was defined, and can be executed later using those definitions, possibly taking some arguments as input as well.

The terminology distinction between blocks and closures probably comes from the days when Smalltalk blocks weren’t closures. That is, they would reference the environment in which they were executed rather than the environment in which they were defined. However, since at least the early 1990s, I believe all major Smalltalk environments have switched to representing blocks as closures.