Can't get System.Numerics to work with command

We're trying to run a simple Mono script on the command line on OS X. Most scripts work fine for us, but as soon as we try to use System.Numerics, we get "error CS0234: The type or namespace name `Numerics' does not exist in the namespace System."

This isn't too surprising, and should be fixable with an appropriate command-line option to mcs, plus properly set up PKG_CONFIG_PATH... but this is where we get stumped. First, here's the script so you can follow along at home:

using System;
using System.Numerics;

public static class MainProgram {
    public static void Main(string[] args) {
        Console.WriteLine("Hello world!");
    }
}

So next we tried "mcs -r:System.Numerics Test.cs". This produces "error CS0006: Metadata file `System.Numerics' could not be found".

"man mcs" suggests that we can get the other system packages by adding "-pkg:dotnet" to the command line. But that produces:

Package dotnet was not found in the pkg-config search path. Perhaps you should add the directory containing `dotnet.pc' to the PKG_CONFIG_PATH environment variable No package 'dotnet' found error CS8027: Error running pkg-config. Check the above output.

OK then, we had no PKG_CONFIG_PATH, so we tried defining one:

export PKG_CONFIG_PATH=/Library/Frameworks/Mono.framework/Versions/Current/lib/pkgconfig/

This fixes the CS8027; but we still get the CS0234 we started with. And if I combine the -pkg and the -r, e.g. "mcs -pkg:dotnet -r:System.Numerics Test.cs", I get "error CS0006: Metadata file `System.Numerics' could not be found".

I'm stumped at this point... any idea what incantation I'm missing to make System.Numerics work with mcs?

If you're using Mono 2.10.x, you will have to compile with dmcs rather than mcs to enable the 4.0 profile (System.Numerics is a C# 4.0+ feature only).

If you're using Mono 2.11.x or 3.0.x, then mcs by default should select the 4.5 profile. mcs -help should show 2, 4, and 4.5 as possible values for the -sdk option. If it doesn't, then the framework isn't properly installed; I had that once, where I think that /Library/Frameworks/Mono.framework/Versions/Current pointed to the wrong directory; installing a second time fixed that.

Manipulating pkg-config should be unnecessary.