Still very much a work in progress but it’s at least 99% there. And what better way to celebrate than with a round of 99 bottles of beer on the wall!
1.1 Do part 2 for a = 99(-1)2.
1.2 Do part 3.
1.3 Line.
2.1 Type a in form 1.
2.2 Type a in form 2.
2.3 Do step 4.1.
2.4 Set b = a - 1.
2.5 Do step 3.1 if b = 1.
2.6 Do step 3.5 if b != 1.
2.7 Line.
3.1 Type "1 bottle of beer on the wall".
3.2 Type "1 bottle of beer".
3.3 Do step 4.1.
3.4 Set b = 0.
3.5 Type b in form 1.
4.1 Type "You take one down, you pass it around".
Form 1:
_._ bottles of beer on the wall
Form 2:
_._ bottles of beer
The PEG.js parser is now complete!!! Now all that is left to do is write the functions for the evaluator and control flow. For now I have locked the parser to only testing commands against MathExp as the root node. The function eval_math(tree) accepts a syntax tree with a root node marked as num for a plain numerical value, var for a reference to a variable, math for a simple add/sub/mult/div between two other math trees, or function which represents a call to a math function (built into the language). Below is an overview of the parse tree for a math expression (MathExp).
Math::Number
{ tag: "num", val: 0 }
Math::Variable
{
tag: "var",
val: {
id: "a",
index: {
// Another Math Expression
}
}
}
Math::Math
{
tag: "math",
val: {
op: "+",
left: {
// Another Math Expression
},
right: {
// Another Math Expression
}
}
}
Math::Function
{
tag: "function",
val: {
func: "sqrt",
param: {
// Another Math Expression
}
}
}
Math::Function (multiple params)
{
tag: "function",
val: {
func: "min",
param: [
{}, // Another Math Expression
{}, // Another Math Expression
{} // Another Math Expression
]
}
}
Progress on the JOSS language simulator is coming along nicely. I decided to take a break from transcribing and converting the grammar so I could work on the ui for a bit. This will be helpful as soon I’ll need a way to parse input commands and output the system replies.
So far the terminal is designed along with the input bar. Upon pressing enter the currently written command is added to the bottom of the terminal feed and (if necessary) the terminal is smoothly scrolled down to it’s new bottom. Like the original typewriter consoles on JOHNNIAC, inputs typed by the user appeared in black type and responses from the system are shown in green.
Further plans for the ui are to eventually include some form of modal or accordion based content organisation to allow a pane describing the history of JOHNNIAC, and a pane to describe the syntax for the language.
As I alluded to at the end of my last post on the subject of the JOSS programming language, my goal is to revive the language and create a usable version of it. (Why, you ask? Why not)
The design for the Simulator is to construct a webpage with a black/green terminal style display with a text box at the base of the terminal to allow command statements to be prepared and submitted to the system. On the backend the simulator will run entirely in Javascript, utilizing the PEG.js parser builder to tokenize and execute commands.
When a command is submitted to the terminal it will be given to PEG.js to parse and turn into a syntax tree of tokens. PEG.js also gives very precise parse errors which will allow the simulator to give the user feedback on their commands. If a command is successfully parsed the parse tree and the text version of the command will either be stored as as elements in the “program tape” a javascript object of the form:
By expressing the entire program and state of the simulator in JSON we gain the ability to easily have access to any part of the program or data. We also have the ability to save the current session using the browser’s local storage api or share the program by simply saving the serialized JSON to the server with a unique link. JSON is also the reason for storing the parse trees as objects rather than compiling them to an intermediary before use. By walking and evaluating a command by climbing through it’s parse tree we can use recursion to jump to other commands in the program tape. When we have fully climbed back up the tree to the root node or a command returns the Stop. token we know the program has finished executing.
One problem I see currently is that the language is based around the use of fixed precision arithmetic using 9 decimal places for precision. Currently I don’t know of any way to do math in fixed precision in JavaScript short of rolling my own set of maths classes, and I’d really rather not. For now we’ll work in standard floating point and see if it can be added in later.
The Grammar
Citation: "JOSS: Experience with an experimental computing service for users at remote typing consoles", J. C. Shaw, May 1965, Page: 10
Using the paper I found previously discussing the use of JOSS on JOHNNIAC over a 16 month period, I have been able to piece together a Context Free Grammar. While I am pretty happy with it, it’s not perfect. Every now and then I spot an error and fix it but for the most part I’m satisfied it’s solid.
There are however a couple of things intentionally in there which aren’t perfect but there is good reason for them. For instance, because JOSS lacks the ability to have user defined functions I have created a function token and within it an array of tokens, each representing a different standard math function available to the user. The reason for this is to allow parse time error checking of the number of variables.
Converting for PEG.js
So far I have gotten numbers and math expressions converted into a PEG.js parser. The current state of the parse can be seen on this Gist along with the BNF Grammar. Eventually I will move all of this into its own repo on Github but for now it’s all being developed in the browser; that is, I’m writing the PEG.js parse directly into their online compiler to test it as I go, so there is nothing local to save to a repo at the moment.
Below is the current BNF Grammar for the language.
My name is Zaphod. Or at least, if my father had had his way my name would be Zaphod.
As the story goes my mother, still light headed and exhausted from child birth had to up and run down to the reception office to stop my father from having the name Zaphod (as in Zaphod Beeblebrox from The Hitchhiker’s Guide to the Galaxy) put on my birth certificate.
Now as uncommon and strange of a name as Zaphod is my parents compromise on the name Joss is arguably just as uncommon. In fact, the only reason you have probably heard the name Joss is because a large proportion of the few people called Joss are famous (no pressure or anything). Joss is also commonly (cough: incorrectly) used as a shortening for Jocelyn.
However, what if my father in fact had another trick up his sleeve? A plan so cunning and dastardly that my mother never would have suspected his evil doing. What if my father named me after a programming language…? He had the knowledge, being a mathematician and programmer at Aldermaston, and he had shown the capability by attempting to name me after a character in a Sci-Fi TV / Radio show & Book series.
The JOSS Language
Today by random happenstance (no I was not Googling my name… who on earth does that? …) I discovered a Wikipedia page about a programming language called JOSS.
JOSS was the child of a 1950’s R&D firm called RAND which quite unimaginatively stands for Reasearch ANd Developement. RAND was funded by the US Army Air Corps which later became the US Air Force, and is still an active organisation today.
RAND developed a computer called JOHNNIAC in 1953. JOHNNIAC, which stood for John v. Neumann Numerical Integrator and Automatic Computer, was soon surpassed by faster and more reliable machines. This however, allowed for other non performance critical research to be carried out on JOHNNIAC; most notably the development and usage of the JOSS programming language.
The JOHNNIAC Open Shop System, JOSS, was the first language which allowed for interactive and concurrent access to a computer. Developed between 1963 and 1964 by Cliff Shaw (inventor of the Linked-List), JOSS allowed for up to eight users to access JOHNNIAC simultaneously via separate typewriter terminals.
The language was designed as a way for mathematicians and engineers to perform small but complicated calculations quickly without having to have a great knowledge of computers or direct access to a “Computer Expert”. JOSS has two methods of interaction, direct and indirect. In direct mode the user presents command statements to the terminal (which were printed in black ink) and JOSS replies to these statements as each arrives (printed in green ink). In indirect mode the user queues up commands by preparing a program, the user then types Go. or types a statement to be run as an initializer which then runs the program.
So was I named after a programming language?
JOSS is openly referred to as JOHNNIAC’s legacy. As it just so happens my father is named John, and by being his only son I am by very definition his legacy. Coincidence? I think not!
After a little more digging trying to find out more about this language I stumbled across this paper published by the RAND Corporation in 1965, describing the results of using JOSS on JOHNNIAC over a period of approximately sixteen months. From this paper, which also gives a good overview of how to use and program in JOSS, a couple of quotes stuck out to me.
People adjust their lives to fit around JOSS… No use coming into RAND before 10:00 am when JOSS arrives, in fact noon or after 5:00 pm is a better time, JOSS is less busy. When JOSS starts typing answers, the titillating pleasure is equalled only by the ensuing anguish when JOSS breaks off into jibberish or goes away commending your code to oblivion. We can hardly live with JOSS, but we can’t live without it.
Now you can’t say that doesn’t sound like me.
JOSS lacks the problem-solving capacity to carry on a sophisticated conversation.
Actually, that sounds a little more like m… nevermind.
So was I named after a programming language? Okay probably not. I actually asked my father and while he betrayed a slightly evil smirk before he began to laugh he claims he and my mother simply chose Joss because it was uncommon.
Where to go from here?
Well I would think that’s obvious don’t you? I am a Computer Scientist name Joss and there is a programming language named JOSS which for all intents and purposes, much like Latin, is a dead language. The next step, clearly, is to find a more formal specification of JOSS or derive one if none exists and create a JOSS interpreter.
For now though I will leave you with this program which looks for a user named Joss, programmed in JOSS, by a programmer named Joss. How meta is that :)
1.1 Type "Are you Joss? (1 or 0)".
1.2 Demand n.
1.3 Do part 2 if n=1.
1.4 Do part 3.
1.5 Stop.
2.1 Type "Hello Joss!".
2.2 Stop.
3.1 Type "You aren't? Only Joss is welcome!".
Go.
Program
