Types, Generics, and Protocols

A Python reader brings habits from names, dictionaries, classes, protocols, exceptions, None, imports, and duck typing. That helps with code around domain words before machinery, but the Musi page asks a narrower question: what contract should this generic behavior contracts example make visible?

from typing import Generic, TypeVar

T = TypeVar("T")

class Box(Generic[T]):
    def __init__(self, value: T):
        self.value = value

let Box [T] := data {
  value : T;
};

let boxedName : Box[String] := {
  value := "Nora"
};
boxedName.value;

Reading Types, Generics, and Protocols from Python

On the Musi side, Musi classes name behavior a type can provide, instances provide it, and laws document promises callers rely on. Read the shared example through Python eyes: keep the useful instinct, then let Musi name shape, behavior, absence, and outside work in separate places.

False friend

Do not confuse a Musi class with stored object state, inheritance, or a metatable. Shape and behavior are separate. For a Python reader, the trap is trusting runtime convention where Musi expects a visible type or effect; Musi class is closer to an explicit protocol/typeclass than a Python class with attributes and methods.

When this pays off

Use classes when many types share an operation such as compare, show, step, encode, or measure. The Python instinct still helps here: Keep the Python habit of naming the real-world thing first.

Keep close

• Generics
• Classes
• Laws