F# Language

This User Voice was for suggestions about the future evolution of the F# Language and Core Library.

I suggest we ...

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  1. Remove fun keyword from lambda expressions

    Maybe make it optional?
    Otherwise it is more verbose than C#.

    270 votes
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      17 comments  ·  Flag idea as inappropriate…  ·  Admin →
    • 7 votes
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        3 comments  ·  Flag idea as inappropriate…  ·  Admin →
      • Support mixed F# and C# projects in order to extend F# usage

        Support mixing F# and C# source files in the same project in order to support a gradual move to F# for new users/organisations and to support cases where tooling is oriented at C# (F# not supported)

        For instance I could use this feature to slowly move a C# project to F# one class at the time. Another example would be to use C# tooling to generate web infrastructure like ASP.NET 5 controllers (because F# does not currently have templates for this) and then call directly into F# from those.

        P.S. Other languages that F# compares to like Scala already supported…

        121 votes
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          6 comments  ·  Flag idea as inappropriate…  ·  Admin →
        • Add ofObj to Seq and Array

          The Option module defines Option.ofObj which converts a potential nullable value to an option.

          Collections (Seq and array) can be null in interop scenarios, but it'd often be natural to interpret a null collection as an empty collection.

          It's possible to compose such behaviour from existing building blocks, e.g. with Option.ofObj >> Option.toArray >> Array.concat

          This seems like quite a roundabout way to do things, so I'd like to propose equivalent functions for Seq and Array:

          // seq<'a> -> seq<'a>
          Seq.ofObj

          // 'a [] -> 'a []
          Array.ofObj

          6 votes
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            1 comment  ·  Flag idea as inappropriate…  ·  Admin →
          • Add many more string manipulation functions to the Core.String module

            The Core.String module does not provide nearly enough features at present, too often we have to revert to using the the standard .NET string class which both hinders tidy piping and stops us taking advantage of curried args / partial application.

            I suggest that at least the following functions be added to the string module:

            empty : string
            isEmpty : string -> bool
            isWhitespace : string -> bool
            replace : string -> string -> string -> string
            startsWith/endsWith : string -> bool
            split : seq<char> -> string -> seq<string>
            toUpper/toLower(Invariant) : string -> string
            trim : string -> string
            trimStart/trimEnd…

            53 votes
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              4 comments  ·  Flag idea as inappropriate…  ·  Admin →
            • Better PR efforts: Write a client library to run F# code on the D-Wave quantum computers

              Quantum computing attracts a lot of attention from scientists and software developers.

              I suggest writing a client library to run F# code on the D-Wave quantum computers in order to improve F# visibility and popularity among software developers and scientists specializing in optimization, machine learning, pattern recognition and anomaly detection, financial analysis, software/hardware verification and validation, scheduling and logistics, bioinformatics.

              The world's first commercial quantum computer (D-Wave One) was built in 2010 by the D-Wave Systems Inc. (offices in Palo Alto, CA, Washington, DC, and Burnaby, British Columbia, Canada). In 2013 the D-Wave Systems Inc. shipped a 512-qubit D-Wave Two…

              2 votes
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                1 comment  ·  Flag idea as inappropriate…  ·  Admin →
              • Return untyped syntax tree from ITypeProvider

                Add the ability to *opt in* to send back an untyped syntax tree from ITypeProviders. The current type provider mechanism is good for simple data exploration use cases, but otherwise extremely limited, and will soon allow for less metaprogramming than Roslyn in some ways. Currently, some types of type providers not possible to create, because unbound generics, records, discriminated unions, and other normal language features are not supported.

                With the ability to opt in to just returning an untyped syntax tree, it would enable the creation of just about any type provider. It would also effectively give F# macros, though…

                27 votes
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                  3 comments  ·  Flag idea as inappropriate…  ·  Admin →
                • Expand on cardinality functions Seq.exactlyOne, with Seq.tryExactlyOne and add oneOrMore, zeroOrMore

                  While it is quite trivial to write these functions, I think they have merit. First of, it is good there's a Seq.exactlyOne, but it throws and if you want a non-throwing version, you'll have to write one your own. It's odd there's a creator function, Seq.singleton, but not a test-function.

                  Since we have Seq.exactlyOne, it should have its logical cardinality counterparts for zero-or-one and one-or-more to be available too.

                  I suggest we add:
                  Seq.tryExactlyOne
                  Seq.oneOrMore (throws)
                  Seq.zeroOrMore (throws)
                  Seq.tryOneOrMore
                  Seq.tryZeroOrMore

                  The reason it is better to have these in FSharp.Core is that, if one implements these by hand, it requires…

                  7 votes
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                    0 comments  ·  Flag idea as inappropriate…  ·  Admin →
                  • Add a warning for new keyword used on types which are not IDisposable

                    This is an alternative to: https://fslang.uservoice.com/forums/245727-f-language/suggestions/15257796-remove-warning-for-new-keyword-on-idisposable

                    The idea is that the new keyword provides valuable information, but only if you do not use it on all types.

                    When avoiding its usage, you get a visual clue as to instances of disposable types, as well as warnings if you bind them.

                    By making it a warning to use new unnecessarily, the compiler would effectively enforce a "best practice" with regards to IDisposable usage. It goes a long way today, but requires discipline to make it useful.

                    This would be especially helpful to people coming to F# from C#, as many immediately…

                    21 votes
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                      0 comments  ·  Flag idea as inappropriate…  ·  Admin →
                    • Allow Object Expressions from abstract base classes without members

                      http://stackoverflow.com/questions/8154730/object-expression-for-abstract-class-without-abstract-members

                      Object Expressions are a great feature to create instances of single-use interface / abstract class instances without polluting the namespace.

                      At the moment it is impossible to inherit from an abstract class which does not define any members.

                      If I have an abstract base class

                      [<AbstractClass>]
                      type Foo(i:int) = class end

                      then I would like to be able to exten it like this:

                      let foo = { new Foo(1) }

                      But this errors out with

                      Invalid object expression. Objects without overrides or interfaces should use the expression form 'new Type(args)' without braces.

                      The suggestion obviously doesn't work, since the…

                      4 votes
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                        0 comments  ·  Flag idea as inappropriate…  ·  Admin →
                      • 2 votes
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                          0 comments  ·  Flag idea as inappropriate…  ·  Admin →
                        • Relax indentation rules on Records

                          The current indentation rules around records seem inconsistent, or at least counter-intuitive. Consider for instance:

                          type Foo = {
                          ....Foo:int
                          ....}

                          type Bar = {
                          ....F:Foo
                          ....}

                          let bar = {
                          ....F = {
                          ........Foo = 10
                          ........}
                          ....}

                          This is valid. But if you change F in Bar to VeryLongName:

                          type Baz = {
                          ....VeryLongName:Foo
                          ....}

                          let baz = {
                          ....VeryLongName = {
                          ........Foo = 10
                          ........}
                          ....}

                          We now get a warning:
                          warning FS0058: Possible incorrect indentation: this token is offside of context started at position (10:20). Try indenting this token further or using standard formatting conventions.

                          In…

                          9 votes
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                            0 comments  ·  Flag idea as inappropriate…  ·  Admin →
                          • Literal sprintf

                            Allow:
                            ```
                            [<Literal>]
                            let a = sprintf "%s" "string"
                            ```

                            16 votes
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                              0 comments  ·  Flag idea as inappropriate…  ·  Admin →
                            • Remove warning for new keyword on IDisposable

                              The only time I ever use the new keyword is on Disposables, and even then only to silence the compiler warnings. I'm not sure what purpose the warning serves either, because you can still forget to bind the disposable with the use keyword instead of with let. What's more annoying is that it prevents you from effective pipelining.

                              Could this be removed from the next F# release, or perhaps replaced with a warning if you bind a Disposable with let instead of use?

                              5 votes
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                                6 comments  ·  Flag idea as inappropriate…  ·  Admin →
                              • Multi-case unions compiled to struct

                                I am posting this idea to be able to track its status since it is already informally under consideration. Tuples, records, and single-cases unions are have already planned (implementation even nearing completoin) to be compilable to a struct:

                                struct tuples: https://fslang.uservoice.com/forums/245727-f-language/suggestions/6148669-add-support-for-structtuple
                                struct records: https://fslang.uservoice.com/forums/245727-f-language/suggestions/6547517-record-types-can-be-marked-with-the-struct-attribu
                                struct single-case unions: https://fslang.uservoice.com/forums/245727-f-language/suggestions/6147144-allow-single-case-unions-to-be-compiled-as-structs

                                There is also already a proof of concept for unions of "blittable" types: https://fslang.uservoice.com/forums/245727-f-language/suggestions/7072844-utilise-clr-union-types-for-discriminated-unions

                                There has also been a lot of discussion on the implementation of multi-case unions in the discussion of struct records: https://github.com/Microsoft/visualfsharp/pull/620

                                One great use of multi-case unions compiled to struct would be optional computations (e.g. Option<'T>) for value…

                                20 votes
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                                  0 comments  ·  Flag idea as inappropriate…  ·  Admin →
                                • 3 votes
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                                    0 comments  ·  Flag idea as inappropriate…  ·  Admin →
                                  • allow compiler directive to switch off inlining

                                    to get around debugging issues with the inline macro device, this pattern creaps into the code base (taken from FsPickler):

                                    #if DEBUG
                                    let writeBoundedSequence
                                    #else
                                    let inline writeBoundedSequence
                                    #endif

                                    It would be nice to be able to turn off the effect of the inline keyword for files and entire projects while compiling for debugging purposes. Also, optionally setting ignore inline for code executed in an interactive session would be useful too.

                                    8 votes
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                                      1 comment  ·  Flag idea as inappropriate…  ·  Admin →
                                    • Provide Intellisense on 'tab' key when creating 'new' classes or types.

                                      I would like to have the ability to hit the "tab key" when creating a new type with a constructor that will list the types available properties.

                                      I C# this is done nicely with classes and as you assign a value the property is no longer available in intellisense when one tabs again to select another property.

                                      1 vote
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                                        0 comments  ·  Flag idea as inappropriate…  ·  Admin →
                                      • Provide property on base Discriminated Union type if all the case constructors have the same paramater

                                        If an each case constructor of Discriminated Union has a parameter with the same name and the same type than allow to implement a property on Discriminated Union base type to access to this parameter value.

                                        Now I have to write a match on every case

                                        type Physical =
                                        | OneToOne of Data : ModuleData * Line : ModuleList
                                        | OneOnOne of Data : ModuleData * Line1 : ModuleList * Line2 : ModuleList
                                        | OneByOne of Data : ModuleData * Line1 : ModuleList * Line2 : ModuleList
                                        | Vertical of Data : ModuleData * Line1 : ModuleList * Line2 :…

                                        27 votes
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                                          2 comments  ·  Flag idea as inappropriate…  ·  Admin →
                                        • Record copy update should be able change the generic type

                                          type A<'a> =
                                          {
                                          mutable x: 'a
                                          }

                                          let a = {x = 1}
                                          {a with x="Hello"} // Type error

                                          Since the x field is generic and F# is type safe, it would not be bad if the above was valid.

                                          1 vote
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                                            0 comments  ·  Flag idea as inappropriate…  ·  Admin →
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