Planned Type System

Passerine’s Type System

Passerine has full support for algebraic data types. It’s structurally typed with support for type refinement at runtime. Passerine’s type system aims to be decidable and sound.

Core Algebraic Data Types

Atoms

Base types that can not be broken down. This includes:

• Booleans
• Numeric Tower
• Strings

Records

product types over a set of fields:

• Fields accessed via indexing
• Defined as: { f1: t1, f2: t2, …, fn: vn }
• Constructed as: { f1: v1, f2: v2, … fn: vn }
• A tuple is a record where each field is a number:
  ( v1, v2, …, vn )
• { a, b, c } is a valid record of type { a, b }. Extra fields are ignored.

Unions

sum types over a set of types:

• Variants accessed via indexing
• Defined as { Variant1 v1, Variant2 v2, …, Variantn vn }
• Constructed as: Label::Variant v
• Variants are scoped, so that, i.e. A::C != B::C. Variants are also proper types in their own right.

Lists

Homogenous growable array of items of a type:

• Items accessed via indexing
• Defined as [ type ]
• Constructed as [ v1, v2, …, vn ]

Labels

Scoped namespaces to distinguish types with different semantics of the same structure. They must be defined with the type keyword:

• Defined as Label <type or none if Label is Defined>
• Constructed as Label value
• Has an attached record for associated values, accessible via indexing.
• If the namespace LabelA (the type) fills the structure of LabelB (the trait), LabelB::LabelA is a valid variant of LabelB.