Contracts in source

A Beskid contract is a structural interface: required members, optional embeddings, checked at compile time when a type lists conformances.

Declaration

contract Disposable
{
    unit Dispose();
}

type Logger : Disposable
{
    unit Dispose() { /* ... */ }
}

Normative detail: Contracts.

Conformance lists

Types declare type Name : I, J { ... }. The compiler checks every required member (E1601–E1607). Conflicting embeddings from two contracts must error—no C#-style diamond denial as a lifestyle.

Embeddings

contract Readable
{
    i32 Read(ref u8 buffer);
}

contract ReadWrite : Readable
{
    i32 Write(ref u8 buffer);
}

Embedding flattens requirements; implementers satisfy the expanded surface once.

Not Mod SDK contracts

Surface	Purpose
contract Foo { ... } in user code	Type conformance, static dispatch
Beskid.Compiler.* mod contracts	Compile-time plugins (Compiler Mod SDK)

Contracts vs classes

Contracts describe capabilities, not inheritance trees. Prefer small contracts composed with embeddings over one “god interface” copied from enterprise slides.

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Effects and purity