rust/src/doc/trpl/glossary.md

% Glossary

Not every Rustacean has a background in systems programming, nor in computer science, so we've added explanations of terms that might be unfamiliar.

Arity

Arity refers to the number of arguments a function or operation takes.

let x = (2, 3);
let y = (4, 6);
let z = (8, 2, 6);

In the example above x and y have arity 2. z has arity 3.

Abstract Syntax Tree

When a compiler is compiling your program, it does a number of different things. One of the things that it does is turn the text of your program into an ‘abstract syntax tree’, or ‘AST’. This tree is a representation of the structure of your program. For example, 2 + 3 can be turned into a tree:

  +
 / \
2   3

And 2 + (3 * 4) would look like this:

  +
 / \
2   *
   / \
  3   4