F# - Array.Parallel module not accessible - module

Question

I can access the Array.Parallel module in F# Interactive but not when compiling.
What might be wrong ? (VS 2010)
namespace X // not sent to interactive
open Microsoft.FSharp.Collections
module M =
let square (a _[]) = Array.map (fun a -> a*a ) // OK
let squareP (a:_[]) = Array.Parallel.map (fun a -> a*a ) // Error: "Parallel" not defined
This code compiles fine in FSI but when part of a project fails:
------ Erstellen gestartet: Projekt: DELETE TEST, Konfiguration: Debug Any CPU ------
C:\Program Files (x86)\Microsoft F#\v4.0\fsc.exe -o:obj\Debug\DELETE_TEST.dll -g --debug:full --noframework --define:DEBUG --define:TRACE --doc:bin\Debug\DELETE_TEST.XML --optimize- --tailcalls- -r:"C:\Program Files (x86)\Reference Assemblies\Microsoft\FSharp\2.0\Runtime\v2.0\FSharp.Core.dll" -r:C:\Windows\Microsoft.NET\Framework\v2.0.50727\mscorlib.dll -r:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\v3.5\System.Core.dll" -r:C:\Windows\Microsoft.NET\Framework\v2.0.50727\System.dll --target:library --warn:3 --warnaserror:76 --vserrors --LCID:1031 --utf8output --fullpaths --flaterrors Module1.fs
C:\work\Goswin\30_F#\16-135_LAD\DELETE TEST\Module1.fs(7,37): Fehler FS0039: Der Wert, Konstruktor, Namespace oder Typ "Parallel" ist nicht definiert.

Answer 1

You are targeting .NET 2.0: -r:"C:\Program Files (x86)\Reference Assemblies\Microsoft\FSharp\2.0\Runtime\v2.0\FSharp.Core.dll"
The Parallel module is implemented via System.Threading.Tasks, which were not introduced until .NET 4.0. Thus the Parallel module doesn't exist on Array in the .NET 2.0 version of FSharp.Core.dll. If you re-target to 4.0 it will work.
It works in FSI because FSI runs in a .NET 4 environment.