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Added entries to explain expression-oriented languages

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Added definitions for 'Expression', 'Expression-Oriented Language' and
'Statement'.
Sorted the definitions alphabetically.
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Jonathan Hansford 2015-07-23 12:24:55 +01:00
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src/doc/trpl/glossary.md
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@ -3,24 +3,12 @@
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.
```rust
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:
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:
```text
+
@ -37,3 +25,39 @@ And `2 + (3 * 4)` would look like this:
/ \
3 4
```
### Arity
Arity refers to the number of arguments a function or operation takes.
```rust
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.
### Expression
In computer programming, an expression is a combination of values, constants,
variables, operators and functions that evaluate to a single value. For example,
`2 + (3 * 4)` is an expression that returns the value 14. It is worth noting
that expressions can have side-effects. For example, a function included in an
expression might perform actions other than simply returning a value.
### Expression-Oriented Language
In early programming languages [expressions] and [statements] were two separate
syntactic categories: expressions had a value and statements did things.
However, later languages blurred this distinction, allowing expressions to do
things and statements to have a value. In an expression-oriented language,
(nearly) every statement is an expression and therefore returns a value.
[expressions]: glossary.html#expression
[statements]: glossary.html#statement
### Statement
In computer programming, a statement is the smallest standalone element of a
programming language that commands a computer to perform an action.