on 3/25/2017 2:34 PM

WebSharper 4 beta-6 contains updates to DOM and JQuery bindings, erased union types, JS output optimizations and fixes.

Visual Studio 2017, F# 4.1 and C# 7 support are coming soon.


  • using FSharp.Compiler.Service 11.0.4. To have optimal compilation speeds, go to a folder in a solution at packages\Zafir.FSharp.\tools and run ./runngen in PowerShell as administrator.
  • #650 Bindings to DOM have been updated to current ECMA specification
  • #652 Bindings to JQuery have benn updated to version 3.1.1
  • #660 Erased union and option types have been added to WebSharper.JavaScript namespace, named Union and Optional. These are similar to Choice and Option types of F#, but work as TypeScript's erased unions in the JS translation. Conversion functions are available under modules Optional and Union.
  • #651 output is using JavaScript strict mode
  • #550 custom structs can now be used in RPC calls
  • #644 F# unions with Constant null case can now be used in RPC calls
  • #642 Local generic functions in F# compile when the compiler does not need the type parameter for custom code generation (macros). If it does, you get an error "Macro name would use a local type parameter. Make the inner function non-generic or move it to module level and mark it with the Inline attribute"
  • #648 JavaScript code output optimizations:
    • Functions taking F# tupled or curried functions as parameters and only fully applying them (in the case of curried parameter) now translates to taking a flat JavaScript function. This means less closure creation and better performance when using functions like List.map2
    • Local F# tupled and curried functions are now converted to flat functions in JavaScript where possible
  • #649 Tail call optimization for F#:
    • let rec expressions with single or mutual recursion
    • Module or class (in default constructor) let rec expressions with single recursive function
    • Class members, calling itself but no other members of the same class annotated with JavaScript (so inlines do not opt-out of optimization). For instance members, the call must be on the current instance.
  • #655 Require and RemotingProvider attributes can take additional object parameters. These will be passed on to the constructors of the resource class and the client-side RemotingProvider instance respectively.
  • WebSharper.Resources.BaseResource is not an abstract class any more. This allows using it with the Require attribute without defining an extra type: ` fsharp [<Require(typeof<Resources.BaseResource>, "//myurl.com/mylib.js")>]`


  • #645 Name conflict in WebSharper.Sitelets.Content from C#
  • #657 Using Name attribute on properties with getter and setter now adds set_ to the name of the setter to disambiguate them.
  • #633 WIG-defined interfaces now can be inherited from with F#/C# code if they contain only method definitions without custom inline annotations. Calling interface members from .d.ts-based bindings now translate properly, but these interfaces can't be inherited from in your code (as they are using special call semantics).
  • #665 Unpacking Scripts/Contents for web projects required the WebProjectOutputDir property, although previously assumed project root as default. This default has been restored for back-compatibility.
  • #668 Printing F# compilation errors and warnings as compiling with fsc.exe would, respecting nowarn, warn, warnon, warneserror flags
  • #667 Fix C# analyzer giving failure warnings on build
  • #669 Async.StartImmediate and Async.StartWithContinuations now start the async immediately as in .NET, possibly finishing synchronously if they contain no bind/combine.
  • #671 Fix a translation bug in optimization around calling curried instance members
  • #673 integer type Parse and TryParse methods follow .NET semantics, checking boundaries and disallowing fractions
  • #677 Fix using Inline on constructors calling into other constructors
  • #678 Fix inlining JavaScript statements, and using return to produce a value
  • #679 exception properties Message and InnerException should work for all exception types
  • #676 Queue and Stack constructors taking a seq<'T> (IEnumerable<T>)

Breaking changes

  • Macro API: MacroResult.MacroNeedsResolvedTypeArg now needs the offending type parameter as a field. You can decide if a type is a type parameter of any kind by using the new IsParameter property.

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