Type System (WIP)

Nevalang has strong static structural type-system

• Strong means that there’s no implicit type convertions
• Static means that semantic analysis for type-safety happens at compile time, not run-time
• Structural means that types are compatible if their structure is compatible. Unlike nominative sub-typing, names of the types does not matter. This also means that type can carry more information than needed and still be compatible.

Base Types

These are types that doesn’t have definition in neva source code. Instead compiler is aware of them and knows how to handle them:

• any
• maybe
• boolean
• integer
• float
• string
• map
• list
• enum
• union
• structure

Any (Top-Type)

any is a top-type. It means that any other type is a sub-type of any. That means you can pass any type everywhere any is expected. However, since any doesn’t tell anything about the type, you cannot pass message of type any anywhere where more concrete type is expected. You need to either rewrite your code without using any or explicitly cast any to concrete type.

Maybe

Maybe represents value that maybe do not exist. One must unwrap maybe before using the actual value.

Boolean

Boolean type has only two possible values true and false

Integer

Integer is 64 bit integer number

Float

Integer is 64 bit floating point number

Strings

Strings are immutable utf encoded byte arrays

Maps

Maps are unordered key-value pairs with dynamic set of keys. All values must have the same type

List

List is a dynamic array that grows as needed. All values in the list must have the same type.

Enums

Enums are set fixed set of values (members) each with its own name. They are represented in memory like integer numbers.

Union

Union is a sum type. It defines set of possible types.

Struct

Structures are product types (records) - compile-time known set of fields with possibly different types.

Custom Types

User is allowed to create custom types based on base-types.

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Further section needs some work. This is WIP document.