`Tracking` - Docs - code examples for all members, functions and types in FSharp.Core

[dsyme]

Related to https://twitter.com/dsymetweets/status/1435311963781861376

This is a tracking issue for adding code examples for all functions, members and types in FSharp.Core.

• An example of the kind of thing that needs to be added is here: https://github.com/dotnet/fsharp/blob/main/src/fsharp/FSharp.Core/option.fsi#L136-L142.
• Once integrated, your examples will appear in the F# core library docs here https://fsharp.github.io/fsharp-core-docs/

Modules and types to do:

• FSharp.Core.Operators (mostly done in FSharp.Core examples added to doc-comments #12211)
• FSharp.Core.String
• FSharp.Core.Printf
• FSharp.Core.Result
• FSharp.Collections.Option
• FSharp.Collections.ValueOption
• FSharp.Collections.List
• FSharp.Collections.Array
• FSharp.Collections.Array.Parallel
• FSharp.Collections.Seq
• FSharp.Collections.Map (module)
• FSharp.Collections.Map (type)
• FSharp.Collections.Set
• FSharp.Collections.Array2D
• FSharp.Collections.Array3D
• FSharp.Collections.Array4D
• FSharp.Collections.HashIdentity
• FSharp.Collections.ComparisonIdentity
• FSharp.Control.Async
• FSharp.Control.Async.CommonExtensions
• FSharp.Control.Async.WebExtensions
• FSharp.Control.Event
• FSharp.Control.Observable
• FSharp.Control.Task
• FSharp.Quotations (started Start quotation examples #12233)
• FSharp.Quotations.BasicPatterns (started Start quotation examples #12233)
• FSharp.Quotations.DerivedPatterns (started Start quotation examples #12233)
• FSharp.Reflection.FSharpType
• FSharp.Reflection.FSharpValue
• FSharp.Core.ExtraTopLevelOperators

[nhirschey]

I could take a stab at the Array module examples over the next several weeks. Some initial attempts: https://github.com/nhirschey/visualfsharp/commit/c9327e18573488a0f34517f9fabc19864c9fc9b4

Quick questions:

1. I see that one line examples are preferred. Should every example fit on one line? For beginners some things might be easier when split across multiple lines:
   • blit

     ///     let source = [| 1; 2; 3 |]
     ///     let sourceIndex = 0
     ///     let target = [| 0; 0; 0 |]
     ///     let targetIndex = 1
     ///     let count = 2
     ///     Array.blit source sourceIndex target targetIndex count 
     ///     target // evaluates to [| 0; 1; 2 |]

   • collect

     ///     let negative xs = xs |> Array.map (fun x -> -1 * x)
     ///     negative [| 1; 2 |] // evaluates to [-1; -2]
     ///     let ys = [| [| 1; 2 |]; [| 3; 4 |] |]
     ///     ys |> Array.collect negative // evaluates to [| -1; -2; -3; -4 |]

2. For functions like Array.averageBy, is it useful to show that it is equivalent to Array.map |> Array.average?

[| 1.0; 2.0 |] |> Array.averageBy (fun x -> -1.0 * x) // evaluates to -1.5
// this is equivalent to
[| 1.0; 2.0 |] |> Array.map (fun x -> -1.0 * x) |> Array.average // evaluates to -1.5 

3. Should there be a column-width limit for examples? Wide examples might be harder to read in tooltips. Here's 2 versions of the same example using different numbers of columns:
   

[baronfel]

One thing I would really encourage people to do is add a lang=fsharp attribute to your code example XML tags. It's not strictly speaking to-spec (IMO the .Net XML Documentation spec is fairly lacking here), but it is used in several places (like FSharp.Formatting and FsAutoComplete) to provide users with language-aware syntax highlighting. Stealing from @nhirschey's examples a bit:

• blit:

///<example>
/// The following sample shows how to copy the first two elements of an array to the 
/// second and third positions of another array:
///
///<code lang="fsharp">
///     let source = [| 1; 2; 3 |]
///     let sourceIndex = 0
///     let target = [| 0; 0; 0 |]
///     let targetIndex = 1
///     let count = 2
///     Array.blit source sourceIndex target targetIndex count 
///     target // evaluates to [| 0; 1; 2 |]
///</code>
///</example>

[dsyme]

@baronfel thank you, yes! Is it used consistently in Fsharp.core today? If not please submit a pr to do that?

We should also mention that here

https://github.com/fsharp/fslang-design/blob/main/tooling/FST-1031-xmldoc-extensions.md

[dsyme]

@nhirschey thank you so much for kicking this off - the examples for Array can be reused for list and seq of course

1. multiline samples are definitely needed. Separate them out and take as much space as you need. For complex functions more discursive text may be needed.

2. Regarding equivalences - I think not.

3. Yes but I'm not sure what it should be. I expect 80. We will move to one-function-per-page docs for fsharp.core fsdocs eventually when much more space will be available so don't restrict up 60

[JYCabello]

Can I take Seq?

[MecuSorin]

I will use those as an exercise for my son in his attempt to learn F#. I am very serious. What he is not able/experienced enough, I will do them myself.

[dsyme]

@JYCabello The same examples should generally be used for Seq, Array, List (with minor adjustment) - so since @nhirschey is starting at the top of Array I recommend you start at the bottom of Seq, alphabetically?

[JYCabello]

I will do. Starting tomorrow.

[MecuStefan]

String is done, working on the List at the moment

[JYCabello]

Got to ask: The examples go between the docs for the params and the return type for any particular reason?

[dsyme]

Got to ask: The examples go between the docs for the params and the return type for any particular reason?

No reason - they should be come after I agree. Please feel free to submit a PR doing a re-ordering

[JYCabello]

Great, will do after that. I just noticed that you specifically mentioned to start on the bottom and I started on the top. Sorry about that. I'll make a PR in a bit to have some progress in and to get some feedback.