A C# .Net Class for calling J

One of my favorite programming tools is J.  In skilled hands J is a spear in a world of bent spoons.  In my day job I rarely encounter programming problems that cannot be brutally dispatched with a few dozen lines of J.  Most accomplished J programmers laud the elegance and power of the language and frequently remark on how learning J changed the way the way they think about programming. If you are intrigued please take a look but a word of caution.  Learning J is like learning Calculus. Don’t expect to progress beyond the trivial without a substantial intellectual effort on your behalf.

J has many strengths but current implementations also have some serious shortcomings.

  1. J’s GUI user interface tools are primitive compared to what you find in Microsoft Visual Studio or Java Eclipse environments.
  2. It is difficult to use J in mixed language projects.  J can make C style API calls and the Windows version sports a COM interface.  Both of these call mechanisms are solid and work well but the C API struggles with many C++ libraries and COM is now considered a legacy technology in Microsoft .Net circles.
  3. .Net executables can call J but J cannot easily call .Net executables. 
  4. There are very few useful J libraries. Python programmers often find complete solutions to their problems in libraries.  With J you often end up writing your own libraries  This fosters an independent frame of mind at the expense of productivity.
  5. Packaging J solutions is largely ad hoc and platform dependent.  It’s not like C# or Java where you get a nice self-contained install package.

To deal with J’s deficiencies I cheat and use other languages and tools. This is getting the best of both worlds or Miley Cryrus’ing  it!  Miley Cryus’ing in Windows environments leads straight to .Net and the premier .Net programming language C#.  J is not a .Net language but J can be called from C# by COM or by C style API calls.  This JServer class uses COM. JServer was inspired by Alex Rufon’s J Wiki essay but differs in that all JServer calls are strongly typed.  There is no point in using strongly typed languages like C# if you are constantly casting objects. Use the type checking Luke!

The following JServerTest code snippet shows JServer calls.

using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using JServerClass;  // add reference to JServer.exe

namespace JServerTest
    class Program
        static void Main(string[] args)
            // create new j exe server - load only the j profile
            JServer js = new JServer(JServer.JScriptType.OnlyProfile);

            // make server visible/invisible/visible
            js.jShowServer = true;
            js.jShowServer = false;
            js.jShowServer = true;

            // do tests - create j nouns 
            // that interface can fetch

            js.jDo("18!:5 ''"); // should be in base locale

            // atoms - rank 0
            js.jDo("byteAtom=. 'A'");
            js.jDo("boolAtom=. 1");
            js.jDo("intAtom=. 42");
            js.jDo("doubleAtom=. 1x1"); // e in j notation

            // arrays of rank 1 and 2 
            // higher rank arrays are not
            // explicitly supported by the C# interface
            js.jDo("boolArray=. ?50#2");
            js.jDo("intArray=. 10 10$?100#10");
            js.jDo("doubleArray=. 5 10$(?50#50) % ?50#50");
            js.jDo("byteArray=. 20 30$'goaheadbyteme'");
            js.jDo("stringArray=. ;:'not by the hair of my chinny chin chin'");
            js.jDo("stringArray2=. 11 7$stringArray");

            // get tests - fetch j nouns
            // get and set are C# overloads

            // rank 0 gets
            byte byteAtom;
            js.jGet("byteAtom", out byteAtom);
            bool boolAtom;
            js.jGet("boolAtom", out boolAtom);
            int intAtom;
            js.jGet("intAtom", out intAtom);
            double doubleAtom;
            js.jGet("doubleAtom", out doubleAtom);

            // rank 1 and/or 2 gets
            bool[] boolArray;
            js.jGet("boolArray", out boolArray);
            int[,] intArray;
            js.jGet("intArray", out intArray);
            double[,] doubleArray;
            js.jGet("doubleArray", out doubleArray);
            byte[,] byteArray;
            js.jGet("byteArray", out byteArray);
            string[] stringArray;
            js.jGet("stringArray", out stringArray);
            string[,] stringArray2;
            js.jGet("stringArray2", out stringArray2);

            // set tests - set copies of 
            // fetched nouns in j and test
            js.jSet("byteAtomC", byteAtom);
            // should be identical - result 1
            js.jDo("byteAtom -: byteAtomC"); 
            js.jSet("boolAtomC", boolAtom);
            js.jDo("boolAtomC -: boolAtomC");
            js.jSet("intAtomC", intAtom);
            js.jDo("intAtomC -: intAtom");
            js.jSet("doubleAtomC", doubleAtom);
            js.jDo("doubleAtomC -: doubleAtom");

            js.jSet("boolArrayC", boolArray);
            js.jDo("boolArrayC -: boolArray");
            js.jSet("intArrayC", intArray);
            js.jDo("intArrayC -: intArray");
            js.jSet("doubleArrayC", doubleArray);
            js.jDo("doubleArrayC -: doubleArray");
            js.jSet("byteArrayC", byteArray);
            js.jDo("byteArrayC -: byteArray");
            js.jSet("stringArrayC", stringArray);
            js.jDo("stringArrayC -: stringArray");

            // no overload for this case - it's not
            // as important as the rank 1 case
            //js.jSet("stringArray2C", stringArray2);

            // Datatable's are supported by the interface
            // as they can be quickly displayed and manipulated
            // in DataGridView objects
            DataTable dt = new DataTable();

            // generate test j datatable representation
            // the interface loads a support locale 
            // CSsrv that contains the necessary
            // j verbs to support these representations
            js.jDo("DTTEST=: testDataTable_CSsrv_ >:?100 10");

            // get the datatable
            dt = js.jGet("DTTEST");

            // set a copy of the datatable 
            // back in j and test equivalence
            // slight differences in floating 
            // number character formats
            // are reconciled with (testDataTableMatch)
            js.jSet("DTTESTC", dt);
            js.jDo("DTTESTC testDataTableMatch_CSsrv_ DTTEST");

            // wait five seconds before shutting
            // down so user can view the j exe server

3 thoughts on “A C# .Net Class for calling J

  1. John,
    I get an error ‘JEXEServerLib’ could not be found when I try to compile the JServer.sln. Am I supposed to download some additional library/files to make this work?

    1. Vijay,

      In the bin diretory of installed J 6.02 systems you will find a jreg.bat file. This command registers the J COM servers. You have to explicitly do this and you must have sufficient rights on your machine to register a COM object. Later versions of J 7 & 8 deprecate the use of COM. I’ve been told that jreg.bat will work for J 7 systems on Windows but I have not tried it. Because J is portable, Linux, Windows, Mac, iPhone, Android, … and COM is pretty much Windows only they are discouraging the use of COM after version 6.0x. Hope that helps — John

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