Initial chain proof of concept.

[nojaf]

An attempt to address fsharp/fslang-design#688.
This is merely a suggestion on how to provide guidance. Nothing has been decided so far.

The gist of this PR is that everything that is SynExpr.DotGet related is being converted to an Expr.Chain. A ChainNode consists of links. Each link is either a dot or something between a dot.

Examples:

A.B.C().D
E.F(fun g -> g).H
I<j>().K[0].L(m,n,o).P

The expression between a dot could be multiple things:

• An identifier such as A or A<b>
• An application with unit A()
• An application with a parenthesis expression A(b) (including lambdas A(fun b -> b))
• An index expression .[A]

Capturing all these different F# AST shapes into one unified model is already a big win.
A lot of very selective AST combinations can now easily be replaced with this. Regardless of the what the style will end up being.

[dawedawe]

Love it

[knocte]

@nojaf shouldn't this single line above have one extra level of indentation?

[nojaf]

No, I don't think so, 64 is the argument of the DotGet application.
Syntactically, this is the equivalent of

let f =
    m
        .Property(fun p -> p.Name)
        .IsRequired()
        .HasColumnName("ModelName")
        .HasMaxLength

f 64

If the application doesn't fit on the rest of the line, the arguments are applied indented on the following line.

f
   64

Another extreme example of this would be:

(try
    id
 with ex ->
     id)
    64

In practice, I would write the code with parentheses

    m
        .Property(fun p -> p.Name)
        .IsRequired()
        .HasColumnName("ModelName")
        .HasMaxLength(64)

[knocte]

I don't know, 64 looks more like the argument that is passed to the last func, and as such, would visually be better place there:

    .Property(fun p -> p.Name)
    .IsRequired()
    .HasColumnName("ModelName")
    .HasMaxLength
        64

But this is just because that 64 is the last one and is not another fluent call (it doesn't start with a dot). If it started with a dot, then I'd agree with you.

[nojaf]

m
    .Property(fun p -> p.Name)
    .IsRequired()
    .HasColumnName("ModelName")
    .HasMaxLength 64
    .HasMaxLength
        64

This is no longer part of the same chain that starts with m.
What you wrote there is:

(m.Property(fun p -> p.Name).IsRequired().HasColumnName("ModelName").HasMaxLength)
     (64.HasMaxLength 64)

You can only add that space at the very end, the same reason "ModelName" is not applied with a space but has parentheses.

[knocte]

I didn't mean to write HasMaxLength twice, that was a typo, I edited my message 5 seconds after posting it