Types

Any value that is contained on the stack and visible to the SOF program has one of a few types. Types form a hierarchy, with certain types being considered subtypes of others. This means that any operation allowed on the parent type is also allowed on the subtype, with possibly diverging behavior.

Any operation may specify the operand types on which it is valid. Supplying any operation with an operand of a different type causes a TypeError.

Some types are considered hidden. This means the user cannot fully interact with them.

Value

Value or Any is used to refer to any type, or the union of all types.

Callable

Subtype of: Value

Any type that can be operated on with the call operator ..

Identifier

Subtype of: Callable

A string-like type for textual identifiers used in name binding.

Invoking a call on an identifier performs name lookup.

Primitive

Subtype of: Callable

Any type that can be specified with a simple literal.

Invoking a call on a primitive performs the identity operation, i.e. it returns the primitive’s value. Boolean is an exception to this.

Number

Subtype of: Primitive

Any numeric type. Arithmetic operations only operate on numbers.

Integer

Subtype of: Number

Integral signed number type. MUST be represented in two’s-complement. All operations perform wrapping arithmetic by default, discarding any carries. Minimum representable range must be $[ -2^{63} ; 2^{63}-1 ]$, i.e. 64 bits.

Decimal

Subtype of: Number

Real number type. The precision required should either match DEC64¹, or IEEE 754-2019² double-precision floating-point. Higher precision is allowed.

A NaN value of unspecified representation MUST be available. Infinite values may be available and may have specific behavior in certain operations in interpreters that support them. Otherwise, infinities have the behavior of NaN.

Boolean

Subtype of: Primitive

Truth value, either true or false.

When called, it takes two elements from the stack and returns the lower one if it is true, or the higher one if it is false.

String

Subtype of: Primitive

A string is a sequence of Unicode code points, represented in UTF-8. Its maximum length may be arbitrarily large.

CodeBlock

Subtype of: Callable

A code block is a list of tokens, created by enclosing these tokens in a pair of braces { and }.

When called, it executes the list of tokens.

Function

Subtype of: Callable

A function is a combination of a list of tokens to be executed and a positive (or zero) integer amount of arguments.

When a function is called, it retrieves a number of values from the stack equal to the number of arguments. Then, it places a Function Nametable on the stack. Then, it places the arguments back on the stack, in the same order.

Object

Subtype of: Value

An object is a key-value store that the user can freely modify. When a method is called on the object, the object is used as a nametable, allowing easy modification via normal definition operations.

Constructor

Subtype of: Callable

A constructor is a special kind of function responsible for object creation.

When called, it creates a new object and is able to initialize that object.