[killbot5000]

The simplest example I can think of is: Map(slice, func)

You can can implement this generically in Go using interface{} types and runtime type checking, but then you have runtime type checking failures.

A java/c++-esque "generics" implementation would be able to type-check at compile time.

[ori_b]

You can implement it in Go using loops, and it's not significantly slower or more error prone.

[hauleth]

Unless you want to implement that on top of your custom structure, like, for example, b-tree. Then you either need to write N different implementations for each separate tree or you need to use `interface{}`.

[crimsonalucard]

Yeah but you can't implement it generically.

That means for every conceivable input type and output type combination you have to have a new MAP or REDUCE function to handle it.

All Modern languages except golang and elm only require one implementation of MAP that can handle all type combinations.

It's called parametric polymorphism.