66 lines
1.9 KiB
Markdown
66 lines
1.9 KiB
Markdown
% Glossary
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Not every Rustacean has a background in systems programming, nor in computer
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science, so we've added explanations of terms that might be unfamiliar.
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### Abstract Syntax Tree
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When a compiler is compiling your program, it does a number of different things.
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One of the things that it does is turn the text of your program into an
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‘abstract syntax tree’, or ‘AST’. This tree is a representation of the structure
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of your program. For example, `2 + 3` can be turned into a tree:
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```text
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+
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/ \
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2 3
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```
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And `2 + (3 * 4)` would look like this:
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```text
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+
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/ \
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2 *
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/ \
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3 4
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```
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### Arity
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Arity refers to the number of arguments a function or operation takes.
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```rust
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let x = (2, 3);
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let y = (4, 6);
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let z = (8, 2, 6);
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```
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In the example above `x` and `y` have arity 2. `z` has arity 3.
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### Expression
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In computer programming, an expression is a combination of values, constants,
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variables, operators and functions that evaluate to a single value. For example,
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`2 + (3 * 4)` is an expression that returns the value 14. It is worth noting
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that expressions can have side-effects. For example, a function included in an
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expression might perform actions other than simply returning a value.
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### Expression-Oriented Language
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In early programming languages, [expressions][expression] and
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[statements][statement] were two separate syntactic categories: expressions had
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a value and statements did things. However, later languages blurred this
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distinction, allowing expressions to do things and statements to have a value.
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In an expression-oriented language, (nearly) every statement is an expression
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and therefore returns a value. Consequently, these expression statements can
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themselves form part of larger expressions.
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[expression]: glossary.html#expression
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[statement]: glossary.html#statement
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### Statement
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In computer programming, a statement is the smallest standalone element of a
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programming language that commands a computer to perform an action.
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