4. Object system¶

This chapter describes the object system.

4.1. Values¶

A value is a the primitive unit of data. “Value” can be abbreviated to “val.” For example, each line of the following example produces a value.

'Foo' # a str value
42    # a num value
{(:Num) Num * 2 } # a fun value

Aside from variables, a value has embedded properties.

4.2. Embedded properties¶

Embedded properties are any data contained in a value not via variables. The following are examples of embedded properties:

the Unicode code point sequence of a str value
the scale and the mantissa of a num value
the sequence of instructions of a fun value

Embedded properties cannot be accessed directly from Kink programs, but can be used by the runtime, or host procedures.

4.3. Variables¶

A variable is a pair of a value and a finite length sequence of Unicode code points. The set of all the variables is defined as: Variables = { (owner, symbol) | owner is a value, and symbol is a finite length sequence of Unicode code points }.

Here, owner is said to be the owner of the variable, and symbol is said to be the symbol of the variable. The variable is said to be a variable of owner.

If a symbol is accepted by [a-z_][a-z0-9_?]*, the symbol is called a function symbol. If a symbol is accepted by ([a-z_][a-z0-9_?]*)?[A-Z][a-zA-Z0-9_?]*, the symbol is called a data symbol.

4.3.1. Variable content¶

A variable has a content. The content is either empty, or a value.

4.3.2. Variable operations¶

There are three primitive operations about variables.

Variable-load operation: Gets the content of a variable. The result is either empty or a value.
Variable-store operation: Sets a value as the content of the variable.
Variable-symbols operation: For value X, gets { symbol | the content of variable (X, symbol) is a value }.

4.3.3. Memory model¶

A variable acts like a non-volatile field of Java.