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

Compiling to a dynamic assembly

You can also compile to a dynamic assembly, which uses the F# Interactive code generator. This can be useful if you are, for example, in a situation where writing to the file system is not really an option.

You still have to pass the "-o" option to name the output file, but the output file is not actually written to disk.

The 'None' option indicates that the initialization code for the assembly is not executed.

let errors2, exitCode2, dynAssembly2 = 
    checker.CompileToDynamicAssembly([| "-o"; fn3; "-a"; fn2 |], execute=None)
     |> Async.RunSynchronously

(*
Passing 'Some' for the 'execute' parameter executes  the initialization code for the assembly.
*)
let errors3, exitCode3, dynAssembly3 = 
    checker.CompileToDynamicAssembly([| "-o"; fn3; "-a"; fn2 |], Some(stdout,stderr))
     |> Async.RunSynchronously