Header menu logo F# Compiler Guide

Hosted Compiler

This tutorial demonstrates how to host the F# compiler.

NOTE: The FSharp.Compiler.Service API is subject to change when later versions of the nuget package are published

NOTE: There are several options for hosting the F# compiler. The easiest one is to use the fsc.exe process and pass arguments.

NOTE: By default compilations using FSharp.Compiler.Service reference FSharp.Core 4.3.0.0 (matching F# 3.0). You can override this choice by passing a reference to FSharp.Core for 4.3.1.0 or later explicitly in your command-line arguments.


First, we need to reference the libraries that contain F# interactive service:

#r "FSharp.Compiler.Service.dll"
open System.IO
open FSharp.Compiler.CodeAnalysis

// Create an interactive checker instance 
let checker = FSharpChecker.Create()

Now write content to a temporary file:

let fn = Path.GetTempFileName()
let fn2 = Path.ChangeExtension(fn, ".fsx")
let fn3 = Path.ChangeExtension(fn, ".dll")

File.WriteAllText(fn2, """
module M

type C() = 
   member x.P = 1

let x = 3 + 4
""")

Now invoke the compiler:

let errors1, exitCode1 = 
    checker.Compile([| "fsc.exe"; "-o"; fn3; "-a"; fn2 |]) 
    |> Async.RunSynchronously

If errors occur you can see this in the 'exitCode' and the returned array of errors:

File.WriteAllText(fn2, """
module M

let x = 1.0 + "" // a type error
""")

let errors1b, exitCode1b = 
    checker.Compile([| "fsc.exe"; "-o"; fn3; "-a"; fn2 |])
    |> Async.RunSynchronously
namespace System
namespace System.IO
Multiple items
namespace FSharp

--------------------
namespace Microsoft.FSharp
namespace FSharp.Compiler
namespace FSharp.Compiler.CodeAnalysis
val checker: FSharpChecker
type FSharpChecker = member CheckFileInProject: parseResults: FSharpParseFileResults * fileName: string * fileVersion: int * sourceText: ISourceText * options: FSharpProjectOptions * ?userOpName: string -> Async<FSharpCheckFileAnswer> member ClearCache: options: FSharpProjectOptions seq * ?userOpName: string -> unit + 1 overload member ClearLanguageServiceRootCachesAndCollectAndFinalizeAllTransients: unit -> unit member Compile: argv: string array * ?userOpName: string -> Async<FSharpDiagnostic array * int> member FindBackgroundReferencesInFile: fileName: string * options: FSharpProjectOptions * symbol: FSharpSymbol * ?canInvalidateProject: bool * [<Experimental ("This FCS API is experimental and subject to change.")>] ?fastCheck: bool * ?userOpName: string -> Async<range seq> + 1 overload member GetBackgroundCheckResultsForFileInProject: fileName: string * options: FSharpProjectOptions * ?userOpName: string -> Async<FSharpParseFileResults * FSharpCheckFileResults> member GetBackgroundParseResultsForFileInProject: fileName: string * options: FSharpProjectOptions * ?userOpName: string -> Async<FSharpParseFileResults> member GetBackgroundSemanticClassificationForFile: fileName: string * options: FSharpProjectOptions * ?userOpName: string -> Async<SemanticClassificationView option> + 1 overload member GetParsingOptionsFromCommandLineArgs: sourceFiles: string list * argv: string list * ?isInteractive: bool * ?isEditing: bool -> FSharpParsingOptions * FSharpDiagnostic list + 1 overload member GetParsingOptionsFromProjectOptions: options: FSharpProjectOptions -> FSharpParsingOptions * FSharpDiagnostic list ...
<summary> Used to parse and check F# source code. </summary>
static member FSharpChecker.Create: ?projectCacheSize: int * ?keepAssemblyContents: bool * ?keepAllBackgroundResolutions: bool * ?legacyReferenceResolver: LegacyReferenceResolver * ?tryGetMetadataSnapshot: FSharp.Compiler.AbstractIL.ILBinaryReader.ILReaderTryGetMetadataSnapshot * ?suggestNamesForErrors: bool * ?keepAllBackgroundSymbolUses: bool * ?enableBackgroundItemKeyStoreAndSemanticClassification: bool * ?enablePartialTypeChecking: bool * ?parallelReferenceResolution: bool * ?captureIdentifiersWhenParsing: bool * [<Experimental ("This parameter is experimental and likely to be removed in the future.")>] ?documentSource: DocumentSource * [<Experimental ("This parameter is experimental and likely to be removed in the future.")>] ?useSyntaxTreeCache: bool * [<Experimental ("This parameter is experimental and likely to be removed in the future.")>] ?useTransparentCompiler: bool -> FSharpChecker
val fn: string
type Path = static member ChangeExtension: path: string * extension: string -> string static member Combine: path1: string * path2: string -> string + 3 overloads static member EndsInDirectorySeparator: path: ReadOnlySpan<char> -> bool + 1 overload static member Exists: path: string -> bool static member GetDirectoryName: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetExtension: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetFileName: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetFileNameWithoutExtension: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetFullPath: path: string -> string + 1 overload static member GetInvalidFileNameChars: unit -> char array ...
<summary>Performs operations on <see cref="T:System.String" /> instances that contain file or directory path information. These operations are performed in a cross-platform manner.</summary>
Path.GetTempFileName() : string
val fn2: string
Path.ChangeExtension(path: string, extension: string) : string
val fn3: string
type File = static member AppendAllLines: path: string * contents: IEnumerable<string> -> unit + 1 overload static member AppendAllLinesAsync: path: string * contents: IEnumerable<string> * encoding: Encoding * ?cancellationToken: CancellationToken -> Task + 1 overload static member AppendAllText: path: string * contents: string -> unit + 1 overload static member AppendAllTextAsync: path: string * contents: string * encoding: Encoding * ?cancellationToken: CancellationToken -> Task + 1 overload static member AppendText: path: string -> StreamWriter static member Copy: sourceFileName: string * destFileName: string -> unit + 1 overload static member Create: path: string -> FileStream + 2 overloads static member CreateSymbolicLink: path: string * pathToTarget: string -> FileSystemInfo static member CreateText: path: string -> StreamWriter static member Decrypt: path: string -> unit ...
<summary>Provides static methods for the creation, copying, deletion, moving, and opening of a single file, and aids in the creation of <see cref="T:System.IO.FileStream" /> objects.</summary>
File.WriteAllText(path: string, contents: string) : unit
File.WriteAllText(path: string, contents: string, encoding: System.Text.Encoding) : unit
val errors1: FSharp.Compiler.Diagnostics.FSharpDiagnostic array
val exitCode1: int
member FSharpChecker.Compile: argv: string array * ?userOpName: string -> Async<FSharp.Compiler.Diagnostics.FSharpDiagnostic array * int>
Multiple items
type Async = static member AsBeginEnd: computation: ('Arg -> Async<'T>) -> ('Arg * AsyncCallback * obj -> IAsyncResult) * (IAsyncResult -> 'T) * (IAsyncResult -> unit) static member AwaitEvent: event: IEvent<'Del,'T> * ?cancelAction: (unit -> unit) -> Async<'T> (requires delegate and 'Del :> Delegate) static member AwaitIAsyncResult: iar: IAsyncResult * ?millisecondsTimeout: int -> Async<bool> static member AwaitTask: task: Task<'T> -> Async<'T> + 1 overload static member AwaitWaitHandle: waitHandle: WaitHandle * ?millisecondsTimeout: int -> Async<bool> static member CancelDefaultToken: unit -> unit static member Catch: computation: Async<'T> -> Async<Choice<'T,exn>> static member Choice: computations: Async<'T option> seq -> Async<'T option> static member FromBeginEnd: beginAction: (AsyncCallback * obj -> IAsyncResult) * endAction: (IAsyncResult -> 'T) * ?cancelAction: (unit -> unit) -> Async<'T> + 3 overloads static member FromContinuations: callback: (('T -> unit) * (exn -> unit) * (OperationCanceledException -> unit) -> unit) -> Async<'T> ...

--------------------
type Async<'T>
static member Async.RunSynchronously: computation: Async<'T> * ?timeout: int * ?cancellationToken: System.Threading.CancellationToken -> 'T
val errors1b: FSharp.Compiler.Diagnostics.FSharpDiagnostic array
val exitCode1b: int

Type something to start searching.