Two questions

[bgrundmann]

Why can I only modify a vector inside a local-var? That is why is there no function:

fun vector-set(v : vector<a>, index: int, assigned: a): vector<a>

Given perceus / reference counting this should be efficient and would allow one to implement for example a classic hash table efficiently?! (This was actually what I wanted to try as my first experiment with koka but immediately failed with this road-block).

Why is the console effect internal? That is I thought it would be neat to implement a expect testing framework (similar to https://github.com/janestreet/ppx_expect) for koka, where a test is a function with console effect, but the calling function intercepts the writes to the console to compare against the expected string. But again that seems to be impossible not for a deep reason internal to koka but let's called implementation choices.

Did I misunderstand something?

[timjs]

It would be indeed nice to have a mutable vector, but I think it needs to be a separate type, something like buffer<h,a> which is a buffer in heap h of elements a. Conversion from/to vectors would be a no-op when uniquely referenced.

[bgrundmann]

Why? I am sure this is obvious if you regularly write in Koka, but to me it is unclear why updating of an element in a vector should be different to updating an element in a struct? Or does updating an element in a struct introduce a heap effect?

[timjs]

Ah, I see what you mean: creating a function set(v, i, x) on vectors which makes a copy of v and sets the ith element to x. Only when v happens to be unique, optimise this and do it in-place.

Should be possible to add something like that as an external function I think, but I don't know the right C incantations.