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1 | % Glossary |
2 | ||
3 | Not every Rustacean has a background in systems programming, nor in computer | |
4 | science, so we've added explanations of terms that might be unfamiliar. | |
5 | ||
c34b1796 AL |
6 | ### Abstract Syntax Tree |
7 | ||
c1a9b12d SL |
8 | When a compiler is compiling your program, it does a number of different things. |
9 | One of the things that it does is turn the text of your program into an | |
10 | ‘abstract syntax tree’, or ‘AST’. This tree is a representation of the structure | |
11 | of your program. For example, `2 + 3` can be turned into a tree: | |
c34b1796 AL |
12 | |
13 | ```text | |
14 | + | |
15 | / \ | |
16 | 2 3 | |
17 | ``` | |
18 | ||
19 | And `2 + (3 * 4)` would look like this: | |
20 | ||
21 | ```text | |
22 | + | |
23 | / \ | |
24 | 2 * | |
25 | / \ | |
26 | 3 4 | |
27 | ``` | |
c1a9b12d SL |
28 | |
29 | ### Arity | |
30 | ||
31 | Arity refers to the number of arguments a function or operation takes. | |
32 | ||
33 | ```rust | |
34 | let x = (2, 3); | |
35 | let y = (4, 6); | |
36 | let z = (8, 2, 6); | |
37 | ``` | |
38 | ||
39 | In the example above `x` and `y` have arity 2. `z` has arity 3. | |
40 | ||
41 | ### Expression | |
42 | ||
43 | In computer programming, an expression is a combination of values, constants, | |
44 | variables, operators and functions that evaluate to a single value. For example, | |
45 | `2 + (3 * 4)` is an expression that returns the value 14. It is worth noting | |
46 | that expressions can have side-effects. For example, a function included in an | |
47 | expression might perform actions other than simply returning a value. | |
48 | ||
49 | ### Expression-Oriented Language | |
50 | ||
51 | In early programming languages, [expressions][expression] and | |
52 | [statements][statement] were two separate syntactic categories: expressions had | |
53 | a value and statements did things. However, later languages blurred this | |
54 | distinction, allowing expressions to do things and statements to have a value. | |
55 | In an expression-oriented language, (nearly) every statement is an expression | |
56 | and therefore returns a value. Consequently, these expression statements can | |
57 | themselves form part of larger expressions. | |
58 | ||
59 | [expression]: glossary.html#expression | |
60 | [statement]: glossary.html#statement | |
61 | ||
62 | ### Statement | |
63 | ||
64 | In computer programming, a statement is the smallest standalone element of a | |
65 | programming language that commands a computer to perform an action. |