Show HN: I implemented generics in my programming language

This are merely instanceof switches. Generics mean that you write

  fun(a,b): return a+b 

and if the a + b is doable, it will be done. You don't need to specify the list of types that accepts this syntax. The difference between this and duck typing is that you can also specify interfaces (or traits in c++) that will say that this type is quackable so

  fun(a ): a.quack()

is reusable. What is the difference between this and simple interface implementation? It took me some time to find this example in the narrowest version possible.

  class  Complex(a T, b T):
    Complex operator+(Complex other): return new Complex(this.a + other.a, this.b+other.b)
    Complex operator-(Complex other): return new Complex(this.a - other.a, this.b-other.b)
    Complex operator*(Complex other):
       return Complex(this.a * other.a - this.b * other.b, this.a * other.b + this.b * other.a)

The generic renders this code reusable, so if only you can create a new type, let's say vector, that supports +,-, and multiply you can have complex algebra on those vectors

You have implemented a form of ‘ad-hoc polymorphism’.

This is different from ‘parametric polymorphism’, which is what people call generics.

If your function changes it's behaviour based on the type, then it's not generic.

Your list_contains function should be able to just do a == comparison regardless of whether it's an int or a string.

This is effectively no different than adding a parameter to one of your non-"generic" functions and just swapping behaviour based on that?

I somewhat disagree. FTA: “If the callsite is some_function(2);, the compiler resolves T as i32 and selects the corresponding branch, returning the value incremented by one. […] The important point is that the decision is driven entirely by type information, not by runtime inspection”

Given that, this isn’t that different from C generics (https://en.cppreference.com/w/c/language/generic.html), and people call that generics, too.

Having said that, even ignoring that this requires all implementations to be in a single source file (yes, you probably could use m4 or #include or whatever it’s called in this language) I do not find this syntax elegant.

Also, one thing that it doesn’t seem to support is generating compiler errors when calling a function with a type that isn’t supported.

Right, but C-style generics really are not generics at all. As other comments point out, they effectively are conpile-time if statements. A generic function would automatically instantiate and generate required code for different call types, and perform the correct operations. The C-style "generics" are a conpile-time switch statement, switching on types.