4Data Type

4.1Overview

A value has a corresponding Data Type that defines its behavior and properties.

Each Data Type is bound with a type name, which usually appears in argument list of function call.

Name spaces for Data Type are completely isolated from those for variable and function names.

As each Data Type has a one-to-one relationship with a corresponding Class, those terms have almost the same meaning within documents in many cases.

Data types are categorized into two types: Primitive Data Type and Object Data Type.

A value of Primitive Data Type holds its content in as small memory as possible. It doesn't include any Environment in it and doesn't have any methods with side effects. Among them are nil, boolean, complex, number, rational, string and symbol types.

A value of Object Data Type owns Object data that is a sort of Environment, which allows operations with side effects. Most Data Types except for what are picked up as Primitive Data Types above belong to this.

4.2Primitive Data Types

Below is a list of Primitve Data Types, which also shows one of the typical ways to instantiate values of each type.

nil

A value of nil type is used to indicate an invalid result or status. It is often used as a returned value of a function when it fails its expected work. A variable nil has a value of nil type.
```
nil
```
Since nil is the only instance of nil type, the term nil can both mean the name of the value and its type.
boolean

Values of boolean type are used to determine whether something is in a true or a false state. Variables named true and false are assigned with a true value and a false value respectively.
```
true  false
```
In a function like if having arguments to check true/false condition and in a logical calculation, false and nil only are determined as a false state while other values are treated as a true state. Note that a zero value of number type is recognized as a true, not a false.
complex

A number literal suffixed by j instantiates a value of complex type that represents a complex number.
```
3.14j  1000j  1e3j
```
See chapter Mathematic Functions for more detail.
number

A number literal without any suffix instantiates a value of number type.
```
3.14  1000  1e3  0xaabb
```
rational

A number literal suffixed by r instantiates a value of rational type that represents a rational number.
```
3r  123r
```
See chapter Mathematic Functions for more detail.
string

A string literal without any suffix instantiates a value of string type.
```
'hello world'

R'''
message text
'''
```
symbol

An identifier preceded by a back quote instantiates a value of symbol type.
```
`foo  `bar
```

4.3Object Data Types Frequently Used

4.3.1List

If one or more elements are surrounced by a pair of square brackets, it would instantiate a value of list type. Any type of value can be an element of lists.

[3, 1, 4, 1, 5, 9]
['hello', 'world', 3, 4, 5]

4.3.2Iterator

If one or more elements are surrounced by a pair of parentheses, it would instantiate a value of iterator type. Any type of value can be an element of iterators.

(3, 1, 4, 1, 5, 9)
('hello', 'world', 3, 4, 5)

To create an iterator that contains only one element, be sure to put a comma afther the element like following:

(3,)

An expression (3) is recognized as an ordinary value of number 3.

Operator .. creates an iterator that generates a sequence of numbers. An expression x..y creates an iterator that generates a sequence starting from x and being increased by one until y.

1..10

An expression x.. creates an iterator that generates a sequence starting from x and being increased by one indefinitely.

1..

Lists and iterators are convertible to each other. For instance, a list can be converted to an iterator by using list#each method like following.

[3, 1, 4, 1, 5, 9].each()

An iterator can be converted to an list by surrounding it with square brackets.

[1..10]

In many cases, an iterator is generated as a value returned from a function, which represents a series of multiple results. The most commonly used function may be readlines, which creates an iterator that reads a stream and returns strings splitted by line.

4.3.3Dictionary

dict is a dictionary that contains key-value pairs as its elements where a key is one of number, string or symbol and a value is of any type.

You can create a dictionary by surrounding key-value pairs by %{ and }.

There are several ways to describe the pairs. The most recommended way is to use => operator between each key and value like following.

%{
    `symbol1 => 'value 1'
    `symbol2 => 'value 2'
    `symbol3 => 'value 3'
}

A pair can also be described as a list containing a key and a value.

%{
    [`symbol1, 'value 1']
    [`symbol2, 'value 2']
    [`symbol3, 'value 3']
}

You can also describe keys and values alternately in one-dimentional format.

%{
    `symbol1, 'value 1'
    `symbol2, 'value 2'
    `symbol3, 'value 3'
}

4.3.4Expression

Any expression preceded by a back quote instantiates a value of expr type.

`(x + y)  `func(x)  `{ println('hello'), x += 1 }

4.3.5Binary

A string literal preceded by b instantiates a value of binary type.

b'\x00\x01\0x02\0x03'