Type safety: push allows inserting incompatible types into typed containers

[timfennis]

Problem

When a container has a known element type, mutating functions like push accept any value because their signatures use Any for the element parameter.

let x = [1];       // List<Int>
x.push(1.0);       // Should be rejected — Float is not Int
for y in x { y + 1 } // Int overload selected, but y could be Float at runtime

Root cause

push is registered as push(List<Any>, Any). The analyser has no way to express that the second parameter must match the list's element type. This affects all generic mutation functions: push, push_front, push_back, insert, append, extend, etc.

Solution

This requires parametric polymorphism (generics) in the type system, so that push can be typed as push(List<T>, T). Special-casing individual functions is not the right approach.

Workaround

Users can use explicit type annotations to catch related issues at declaration or assignment sites, but the push call itself won't be caught.