Fennel wiki: Unity

using UnityEngine;
using NLua;
using System.IO;

public class NLua : MonoBehaviour
{
    Lua lua = new Lua();
    public TextAsset fennelLibrary;
    public TextAsset[] fennelScripts;

    private void Awake()
    {
        EnsureFilesExistInPath();
        ConnectLuaToCLR();
        SetupPathsAndScripts();
        Example();
    }

    /// <summary>
    /// This is needed to ensure the fennel.lua library is stored in a path unity and lua can access easily.
    /// It also serves loading any .fnl scripts in the same directory.
    /// There are many ways to do this, this way lets you keep your lua/fnl scripts contained in the unity build, 
    /// and work on multiple traget platforms with their conventions.
    /// Note that this overwrites the scripts in Application.persistentDataPath every time, you may want to version and check that in production
    /// </summary>
    void EnsureFilesExistInPath()
    {
        // fennel.lua Library
        File.WriteAllText(Application.persistentDataPath + "/" + fennelLibrary.name, fennelLibrary.text);

        // .fnl scripts
        for (int i = 0; i < fennelScripts.Length; i++)
        {
            File.WriteAllText(Application.persistentDataPath + "/" + fennelScripts[i].name, fennelScripts[i].text);
        }
    }

    /// <summary>
    /// This allows you to access .Net and Unity from within lua.
    /// It sets a reference to this MonoBehaviour for easy access in lua/fnl
    /// it also overrides import to prevent loading .Net assemblies (optional, remove if needed)
    /// </summary>
    void ConnectLuaToCLR(bool preventImport = true)
    {
        lua.LoadCLRPackage();
        lua["NLua"] = this;
        if (preventImport) lua.DoString("import = function () end");
    }

    void SetupPathsAndScripts()
    {
        // Append package.path with where we stored our .lua/.fnl files
        lua.DoString("package.path = package.path .. \";" + Application.persistentDataPath + "/?/?.lua;" + Application.persistentDataPath + "/?.lua\"");

        // Require fennel, fix path, and allow us to use require on .fnl files
        lua.DoString("fennel = require(\"fennel\")");
        lua.DoString("table.insert(package.loaders or package.searchers, fennel.searcher)");
        lua.DoString("fennel.path = fennel.path .. \";" + Application.persistentDataPath + "/?/?.fnl;" + Application.persistentDataPath + "/?.fnl\"");

        // Load fennel scripts through unity placed files
        for (int i = 0; i < fennelScripts.Length; i++)
        {
            string name = fennelScripts[i].name.Replace(".fnl", "");
            Log("Requiring fennel package:" + name);
            lua.DoString(name + " = require(\"" + name + "\")");
        }
    }

    void Example()
    {
        // Example fennel evaluation using overridden print to log in Unity
        lua.DoString("fennel.eval(\"(print (+ 1 2 3 4))\")");

        // Example fennel evaluation with numeric storage, and retrieval in unity
        lua.DoString("result = fennel.eval(\"(scripts.print-and-add :wow 9 9)\")");
        double? result = (double?)lua["result"];
        if (result.HasValue) Debug.Log("result " + result.Value);

        // Example fennel evaluation with string storage, and retrieval in unity
        lua.DoString("stringResult = fennel.eval(\":my-string\")");
        string stringResult = (string)lua["stringResult"];
        if (!string.IsNullOrEmpty(stringResult)) Debug.Log("stringResult " + stringResult);
    }

    public void Log(object log)
    {
        Debug.Log("Lua: " + log.ToString());
    }
}

public LuaFunction evalInRepl;
public void SetEvalInRepl(LuaFunction luaFunction) { evalInRepl = luaFunction }
public void OnValues(LuaTable vals) 
{
    foreach (var item in vals.Values)
    {
        Debug.Log("OnValues " + item.ToString());
    }
}

// Start the repl and save the SetInput reference
lua.DoString("fennel.eval(\"(NLua:SetEvalInRepl (scripts.start-repl))\")");

// Use the evalInRepl reference after some input (hardcoded string here)
evalInRepl.Call("(* 1 2 3)");

using NLua;

public static class LuaExtensions
{
    public static void DoFnlString(this Lua lua, string chunk, string saveTo = null)
    {
        string prefix =  string.IsNullOrEmpty(saveTo) ? "" : saveTo + " = ";
        chunk = chunk.Replace("\"", "\\\"");
        lua.DoString(prefix + "fennel.eval(\"" + chunk + "\")");
    }
}

// equivalent to calling fennel.eval(...) as we did before
lua.DoFnlString("(scripts.print-and-add :wow 9 9)");

// equivalent to calling result = fennel.eval(...) as we did before
lua.DoFnlString("(scripts.print-and-add :wow 9 9)", "result");

using System.IO;
using UnityEngine;
using UnityEditor;
using UnityEditor.AssetImporters;

[ScriptedImporter(1, "fnl")]
public class FennelScriptedImporter : ScriptedImporter
{
    [SerializeField] private TextAsset fennel;

    public override void OnImportAsset(AssetImportContext ctx)
    {
        fennel = new TextAsset(File.ReadAllText(ctx.assetPath));
        ctx.AddObjectToAsset("Fennel Script", fennel, Resources.Load<Texture2D>("Icons/Fennel"));
        ctx.SetMainObject(fennel);
    }

    [MenuItem("Assets/Create/Fennel Script", false, 80)]
    public static void Create()
    {
        string filename = "myfnlmodule.fnl";
        string content = "(print :hello-world)\n";
        ProjectWindowUtil.CreateAssetWithContent(filename, content);
    }
}