Allow undentation in method and constructor calls

[toburger]

Allow undentation in method and constructor calls

I propose we allow undentation in method and constructor calls without emitting a warning.

The existing way of approaching this problem in F# is that the arguments need to be placed more on the right side of the equal and the caller subject.

Sample:

This is possible today:

let x = System.DateTime(
            year = 2020,
            month = 12,
            day = 1)

also this:

let x =
    System.DateTime(
        year = 2020,
        month = 12,
        day = 1)

and:

let x =
    System.DateTime(
        year = 2020,
        month = 12,
        day = 1
    )

This gives a warning (FS0058):

let x = System.DateTime(
    year = 2020,
    month = 12,
    day = 1)

and likewise:

let x = System.DateTime(
    year = 2020,
    month = 12,
    day = 1
)

also this gives a warning (but is okay in constructors via dotnet/fsharp#6808):

let x = System.DateTime(year = 2020,
    month = 12,
    day = 1)

Sidenote:

Also this way of defining constructors or methods gives a warning:

type Foo (
    y: int,
    x: int) =
    member self.Bar(
        a: int,
        b: int) =
        ()

but this is okay:

type Foo (y: int,
    x: int) =
    member self.Bar(a: int,
        b: int) =
        ()

which was mentioned in #724 (comment) but apparently didn't made it into the PR...

Pros and Cons

The advantages of making this adjustment to F# is a visually more pleasant way of calling methods. Style and elegance is a very subjective view but it goes hand in hand with the relaxed indentation for lists and arrays introduced in F# 4.5 and the "elmish" style formatting.

The disadvantages of making this adjustment to F# are: (too much?) choices!

Extra information

Estimated cost (XS, S, M, L, XL, XXL): S?

Related suggestions: (put links to related suggestions here)

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• This is not a question (e.g. like one you might ask on stackoverflow) and I have searched stackoverflow for discussions of this issue
• I have searched both open and closed suggestions on this site and believe this is not a duplicate
• This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it.

Please tick all that apply:

• This is not a breaking change to the F# language design
• I or my company would be willing to help implement and/or test this

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[Swoorup]

I have always been tripped up due to this. Now, I made peace realising F# doesn't like restrictions on number of columns, so just allowed it span across horizontally when creating class with large number of params/dependencies. This suggestion would make sense. And is common on C#/any C-style language as well.

[Tarmil]

When I have a large number of arguments on a method or constructor, I usually write it like this, which doesn't give any warnings:

    member this.Method
        (
            arg1: int,
            arg2: int,
            arg3: int,
            arg4: int
        ) =
        body

but I agree that it would be nice to be able to put the opening parenthesis at the end of the previous line.

[charlesroddie]

@Tarmil the current problem with undentation of arguments in method or constructor definitions is covered by RFC FS-1070 but there is an incompleteness in the implementation.

@toburger do you think

let x = System.DateTime(
    year = 2020,
    month = 12,
    day = 1)

is superior to

let x =
    System.DateTime(
        year = 2020,
        month = 12,
        day = 1)

?

If not - and to me the latter looks more structured -, wouldn't a better solution be tooling to convert the former into the latter?

[toburger]

I would write it like:

let x = System.DateTime(
    year = 2020,
    month = 12,
    day = 1
)

I find this style very structured and this coding style aligns well with the existing "elmish" style formatting where lists are written like:

let xs = [
    "foo"
    "bar"
    "baz"
]

But as I already said it is a matter of personal taste.
I for myself don't mind requiring too much vertical space but horizontal space really bugs me and I find it hard to scan.

[charlesroddie]

I see. It does seem close to the list notation so that's a good comparison.

[dsyme]

Where is the proposed limit to the undentation? is it 1-space indentation from the let? e.g. consider these:

let x = System.DateTime(
 year = 2020,
 month = 12,
 day = 1
)

and this (ugh)

let x = System.DateTime(
year = 2020,
month = 12,
day = 1)

and this (ugh)

let f() =
    let x = System.DateTime(
 year = 2020,
 month = 12,
 day = 1
)

In general the let form a hard line :)

[dsyme]

Completed in preview dotnet/fsharp#11772

[dsyme]

Completed in F# 6