Hi,
> How to implement heterogen lists in nim? In FP languages we've access to
> better pattern matching and sum types but in nim I can't reproduce them
> properly. I've tried it two different ways:
1\. this one fails because it can't infer the type of any(auto) - I need a
third type parameter which should be optional:
type
HListKind = enum hkNil, hkCons
HList*[H, T] = ref object of RootObj
case kind*: HListKind
of hkNil:
isEmpty*: bool
of hkCons:
head*: H
tail*: HList[T, any]
let hNil*: HList[void, void] = HList[void, void](kind: hkNil, isEmpty: true)
proc hList*[H, T](hd: H, tl: HList[T, any] = hNil): HList[H, T] =
HList[H, T](hd, tl)
Run
2\. this one doesn't fail but I don't know how to iterate over it:
type
HList*[H] = ref object of RootObj
isEmpty*: bool
HNil = ref object of HList[void]
HCons*[H, T] = ref object of HList[H]
head*: H
tail*: HList[T]
let hNil* = HNil(isEmpty: true)
proc hList*[H](hd: H): HList[H] =
HCons[H, void](head: hd, tail: hNil, isEmpty: false)
proc hList*[H, T](hd: H, tl: HList[T]): HList[H] =
HCons[H, T](head: hd, tail: tl, isEmpty: false)
Run
Normally, I'd just use pattern matching but Nim doesn't support it so I'm stuck.
