New method: Sequence.Traverse about morelinq

[atifaziz]

About to delete my previous comment, which was unnecessarily wordy...

A few notes...

1. There is a concept from functional programming called an "unfold", which is the projection of a single entity into a collection via a repeated or recursive operation. Our Generate method in its current form is a special case of the "unfold" operation. It supports value-based unfolding well, but when you start working with more complex objects, usability breaks down.

2. An "unfold" on complex objects is much more of a graph transformation operation than a querying/filtering operation. So far, LINQ itself as well as MoreLinq have been focused on querying and filtering. It may be that the more general "unfold" is useful, but more appropriately bundled with similar functionality. FWIW, I would argue that querying/filtering is a special case of graph transformation, and a querying/filtering DSL (even up to and including SQL itself) could benefit greatly from access to more general graph transformation operations. But MoreLinq may not be the place to start providing this.

3. The Generate name pairs up well with its inverse operation provided in the .NET Framework v3.5: Aggregate. Were we working in a functional environment rather than procedural, these would probably be called Unfold and Fold, respectively. But since we can't change Aggregate, I'm in favor of keeping the Generate name or something similarly untuitively connected to Aggregate.

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Reported by @cammerman on 2009-03-10 23:49:42

[atifaziz]

No problem. I only just noticed Jared Parson has put together a lot of his excellent work on
functional/immutable coding as a library called BclExtras on the MSDN code gallery. It has a lot of interesting stuff and looks a little closer to what I was looking for - it sounds like you have a specific plan for what MoreLinq will cover.

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Reported by daniel.earwicker on 2009-03-21 09:54:42

[atifaziz]

Reported by @atifaziz on 2009-04-04 19:28:51

• Labels added: Type-Enhancement
• Labels removed: Type-Defect

[leandromoh]

As already mentioned by CAmmerman, unfold function can solve it;

Exception innermost = Unfold(caught, e => e.InnerException != null ? Tuple.Create(e, e.InnerException) : null).Last();

[leandromoh]

@atifaziz will you close this issue now that unfold were implemented ?

[atifaziz]

@leandromoh Yep & thanks for helping & remembering to triage this.

[atifaziz]

In the final form Unfold was released in 2.3, the example of traversing nested exceptions to find the innermost will look like this:

var innermost = 
    MoreEnumerable.Unfold(caught, e => e, e => e != null, e => e.InnerException, e => e)
                  .Last();