Side-effects (pure/inpure)

[emil14]

Is it a good idea to mark runtime functions as "pure" and "non-pure" so any component that uses them is also pure/unpure so we can somehow separate side-effects from the rest of the program? Do we have to use something like IO monad (whatever that is)?

Problems

Interface nodes

If component uses DI (has abstract nodes) then it's not clear will it be pure or not

[emil14]

Mark interfaces as pure/unpure

Problem - interface can have many implementations

E.g. mocking network requests in tests

[emil14]

Mark all components with DI as inpure

Problem - such component can be actually pure

[emil14]

Make pureness a property of node, not a component

Node is an instance of a component (BTW shouldn't we use term "instance" instead?) so it's possible for compiler to infer whether node is pure or not - a node is pure if

• The component it's based on has no impure nodes in it's spec/def
• if that component has DI, it must be instantiated without impure nodes

Problem 1. How to use it?

[emil14]

Ask chatGPT

Especcialy about #228 (comment) and how is this works in languages with explicit purity (like Haskell?) and what are examples of such languages

[emil14]

Directives

Could be implemented via compiler directives #354

[emil14]

Purity rules. Interfaces are always "pure"

• Component that use only pure components is also pure. Including component with interfaces
• Interface has no concept of purity. It's abstract and has no dependency on concrete implementation
• Component's node is pure if it's an instance of pure component with only pure deps
• Pure dependencies means all component's deps are injected as pure component instances
• At the lower level purity depends on usage of "atomic" components from stdlib that are manually marker as pure/impure

This approach could help e.g. separate business logic from adapters. Business logic could be pure and completely depend on interfaces which is good for testing.

Examples: math package is pure and fmt or runtime packages are not. runtime.Panic component is impure so any component that use it is also impure. Impurity will be propagated from bottom to top