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Add LazyList.consLazy #134
Description
Description
Conceptually, a LazyList<'T> contains a head of type 'T and a tail of type Lazy<LazyList<'T>>. Strangely, there is no direct way to construct such a lazy list using the current API. The best can be done is LazyList.consDelayed head (fun () -> tail.Value), which is unnecessarily wasteful.
I suggest a new function for creating such a list: LazyList.consLazy (head : <'T>) (tail : Lazy<LazyList<'T>>).
For bonus points, also provide an infix operator that can be used for clarity. I suggest something like (@).
Desired result
I should be able to create an infinite list of 1's like this: let rec ones = 1 @ lazy ones.
Known workarounds
consDelayed can be used but it is inelegant and wasteful.
Activity
gdziadkiewicz commentedon Oct 13, 2019
In F#
@is the list concatenation operator. To make it more aligned with the language shouldn't it be something along the lines of cons::?feat: add LazyList.consLazy for constructing from Lazy<LazyList<'T>>
github-actions commentedon Mar 13, 2026
gdziadkiewicz commentedon May 16, 2026
@copilot Add override for the
@operator that doesconsLazygithub-actions commentedon Oct 22, 2026
🤖 This is an automated response from Repo Assist.
LazyList.consLazyis now onmain(src/FSharpx.Collections/LazyList.fsi, with tests inLazyListTests.fs), so the original request looks fulfilled.On the follow-up about
@: in F#(@)is a fixed list-only function rather than an overloadable operator. A type can't override it, and shadowing it globally would break list append. A custom infix operator such as@@is the practical route, if one is wanted.Unless an operator is still wanted, this issue could probably be closed.
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