为什么 Q# 没有检测到 F# 或 C# 命名空间？

Question

I am making a library in Q# and trying to add a project reference to an F# (or C#) library written by me. But it does not work.

After adding the appropriate reference, I checked my Q# project.csproj file and I could see that the reference was added there that means the process of adding was done properly. But when I try to run the code I receive this message: "error QS6104: No namespace with that name exists" which refers to the line including the name of that F# (or C#) library. I wonder why it happens. Is it due to some fundamental differences between Q# and F# but Q# is created based on F# and C# therefore is there any solution to solve the problem? Here is my code snippet:

    namespace MyQSharpLibrary
    {
        open Microsoft.Quantum.Canon;
        open Microsoft.Quantum.Intrinsic;
        open MyFSharpLib;
        ...
        ...
    }

MyFSharpLib is the library I defined in F# and after adding reference to it inside "MyQSharpLibrary" I can see following markdown code in MyQSharpLibrary.csproj:

    <Project Sdk="Microsoft.NET.Sdk">
      ...
      ...
       <ItemGroup>
        <ProjectReference Include="..\MyFSharpLib\MyFSharpLib.fsproj"/>
       </ItemGroup>  
    </Project>

But after running MyQSharpLibrary, I receive error message: "error QS6104: No namespace with that name exists" which refers to the line containing "open MyFSharpLib;"

Answer 1

open directives in Q# only allow you to import Q# code, not F# or C# code. Q# does not in general allow execution of arbitrary classical code, since it is designed to be executed on a quantum device which in general might not have this ability.

---

If you're looking for a workaround that can be done in a simulation but will not be portable to a quantum device, you can write a simulator that extends one of the existing ones and exposes new intrinsic functions to Q# code that implement your classical computation.

For example, take a look at what the Quantum Katas do to gather statistics about the program execution: they define CounterSimulator which implements intrinsic functions such as GetOracleCallsCount , and a matching Q# code in Utils.qs which exposes them to Q# code. Then this project is added as a dependency to the katas that need this functionality, for example, DeutschJozsaAlgorithm - you'll see the project reference in DeutschJozsaAlgorithm.csproj file and a matching open Quantum.Kata.Utils; in Tests.qs .