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Advanced/Esoteric Languages/main.tex Executable file
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% use [nosolutions] flag to hide solutions.
% use [solutions] flag to show solutions.
\documentclass[
nosolutions,
singlenumbering
]{../../resources/ormc_handout}
\usepackage{../../resources/macros}
% Factorial (print x! from x=0 onwards)
% >++++++++++>>>+>+[>>>+[-[<<<<<[+<<<<<]>>[[-]>[<<+>+>-]<[>+<-]<[>+<-[>+<-[>
% +<-[>+<-[>+<-[>+<-[>+<-[>+<-[>+<-[>[-]>>>>+>+<<<<<<-[>+<-]]]]]]]]]]]>[<+>-
% ]+>>>>>]<<<<<[<<<<<]>>>>>>>[>>>>>]++[-<<<<<]>>>>>>-]+>>>>>]<[>++<-]<<<<[<[
% >+<-]<<<<]>>[->[-]++++++[<++++++++>-]>>>>]<<<<<[<[>+>+<<-]>.<<<<<]>.>>>>]
%
% Same, fibonacci:
% >++++++++++>+>+[
% [+++++[>++++++++<-]>.<++++++[>--------<-]+<<<]>.>>[
% [-]<[>+<-]>>[<<+>+>-]<[>+<-[>+<-[>+<-[>+<-[>+<-[>+<-
% [>+<-[>+<-[>+<-[>[-]>+>+<<<-[>+<-]]]]]]]]]]]+>>>
% ]<<<
% ]
% https://brainfuck.org/fib_explained.b
%
% Useful:
% https://brainfuck.org/
%
%
% +++[[<+>>++<-]>]
% This sets up the tape in the format 3*n^2, which looks like
% 3 6 12 24 48 96 192 128 0 0
% Why is this so important?
% Let's go down the list:
% - 3 and 6 are boring
% - 12: Close to 10 (newline) or 13 (carriage return). Can also be used for the counter for 0-9
% - 24: Close to 26, the number of letters in the alphabet
% - 48: ASCII for 0
% - 96: Close to 97, ASCII for a
% - 196 and 128: 196-128=64, close to 65, the ASCII for A.
\uptitlel{Advanced 2}
\uptitler{\smallurl{}}
\title{Esoteric Programming}
\subtitle{Prepared by Mark on \today}
\begin{document}
\maketitle
\input{parts/00 turing.tex}
\input{parts/01 befunge.tex}
\end{document}

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Advanced/Esoteric Languages/parts/00 turing.tex Executable file
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\section{Turing}
\definition{}
An \textit{esoteric programming langauge} is a programming langauge made for fun. \par
We'll work with two such languages today: \textit{Turing} and \textit{Befunge}.
\definition{}
\textit{Turing} is one of the most famous esoteric langauges, and is extremely minimalist. \par
It consists only of eight symbols, a data pointer, and an instruction pointer.
Turing's eight symbols are as follows:
\begin{itemize}[itemsep=2mm]
\item \texttt{>} : move the instruction pointer right
\item \texttt{<} : move the instruction pointer left
\item \texttt{+} : increment the current memory cell
\item \texttt{-} : decrement the current memory cell
\item \texttt{.} : output the value of the current cell as a character
\item \texttt{,} : consume one character from input and store it at the current cell
\item \texttt{[} : Jump to the matching \texttt{]} if the current cell is zero. \par
otherwise, execute the next instruction.
\item \texttt{[} : Jump back to the matching \texttt{]} if the current cell is not zero. \par
otherwise, execute the next instruction.
\item All other characters are ignored.
\end{itemize}
\problem{}
Go to \href{https://langs.betalupi.com/}{\texttt{langs.betalupi.com}} and open the Turing editor. \par
Clear the pre-set program in the left side of the screen and replace it with the following:
\begin{center}
\texttt{>+>++>+++>++++>+++++[[-]<]}
\end{center}
\begin{itemize}
\item What does this program do?
\item What does the snippet \texttt{[-]} do?
\item Why is the first cell left as \texttt{0}?
\end{itemize}
\vfill
\pagebreak
\remark{}
Run the program \texttt{+[+]}. Notice that the cell's value \textit{wraps}
from \texttt{127} to \texttt{-128}! \par
\vspace{2mm}
Note that \texttt{[+]} has the same effect as \texttt{[-]}.
\vfill
\problem{}
Write a program that moves the value of the current cell three cells to the right.
\problem{}
Write a program that \textbf{copies} the value of the current cell into the next cell.
\begin{solution}
Use a third \say{scratch} cell.
\end{solution}
\problem{}<bfadd>
Write a program that adds the value of the first cell and the second cell,
leaving the result in the second cell.
\problem{}
Solve \ref{bfadd} again, but multiply the two cells instead of adding.
\problem{}
Write a program that computes the square of the current cell.
\vfill
\pagebreak
\definition{}
Turing uses ASCII to map numbers to characters. \par
You may use
\href{https://www.cs.cmu.edu/~pattis/15-1XX/common/handouts/ascii.html}{\texttt{cs.cmu.edu/~pattis/15-1XX/common/handouts/ascii.html}}
for reference.
\vspace{5mm}
\problem{}
Write a program that prints the letter \texttt{a}.
\problem{}
Write a program that prints the alphabet as shown below: \par
\begin{center}
\texttt{abcdefghijklmnopqrstuvwxyz}
\end{center}
\problem{}
Modify your program so that it prints the alphabet with alternating case:
\begin{center}
\texttt{aBcDeFgHiJkLmNoPqRsTuVwXyZ}
\end{center}
\problem{}
Write a program that repeats the user's input exactly as it is entered.
\begin{solution}
\texttt{,[.,]}
\end{solution}
\problem{}
Write a program that repeats the user's input in reverse
\vfill
\pagebreak
\problem{}
Write a program that prints \say{Hello World}
\problem{}
Write a program that finds the first memory cell that is non-zero.
\problem{}
Write a program that initializes the tape with the following sequence:
\begin{center}
\texttt{3 6 12 24 48 96 192 128 0}
\end{center}
\problem{}
Write a program that decodes run-length encoding.
That is, it turns input like
\begin{center}
\texttt{a3j4k2d5}
\end{center}
into the decoded output
\begin{center}
\texttt{aaajjjjkkddddd}
\end{center}
\vfill
\problem{Bonus}
Write a program that prints a Turing program that prints the original program's input.
\problem{Bonus}
Write a program that outputs all squares between 0 and 400 %10,000
\problem{Bonus}
Write a program that prints the Fibonacci numbers
\begin{solution}
\href{https://brainfuck.org/fib\_explained.b}{\texttt{https://brainfuck.org/fib\_explained.b}}
\end{solution}
\vfill
\pagebreak

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Advanced/Esoteric Languages/parts/01 befunge.tex Executable file
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\section{Befunge}
\definition{}
\textit{Befunge} is another esoteric programming langauge, designed to be very difficult to compile. \par
It consists of a \say{field} of instructions, a two-dimensional program counter, and a stack of values. \par
\vspace{2mm}
The program counter starts in the top-left corner of the field, moving right. \par
It executes any instruction it encounters.
The instructions \texttt{>}, \texttt{<}, \texttt{\^}, and \texttt{v} can be used to direct the program counter,
and \texttt{\_} and \texttt{|} are used for control flow.
\vfill
An instruction reference is below:
\begin{itemize}[itemsep=2mm]
\item \texttt{+} Addition: Pop two values $a$ and $b$, then push the result of $a+b$
\item \texttt{-} Subtraction: Pop two values $a$ and $b$, then push the result of $b-a$
\item \texttt{*} Multiplication: Pop two values $a$ and $b$, then push the result of $a \times b$
\item \texttt{/} Integer division: Pop two values $a$ and $b$, then push the result of $b \div a$, rounded down.
\item \texttt{\%} Modulo: Pop two values $a$ and $b$, then push the remainder of the integer division of $b \div a$.
\item \texttt{!} Logical NOT: Pop a value. If the value is zero, push 1; otherwise, push zero.
\item \texttt{ \`} Greater than: Pop two values $a$ and $b$, then push 1 if $b>a$, otherwise zero.
\item \texttt{>} Program counter direction right
\item \texttt{<} Program counter direction left
\item \texttt{\textasciicircum} Program counter direction up
\item \texttt{v} Program counter direction down
\item \texttt{?} Random program counter direction
\item \texttt{\_} Horizontal \texttt{if}: pop a value; set direction to right if value=0, set to left otherwise
\item \texttt{|} Vertical \texttt{if}: pop a value; set direction to down if value=0, set to up otherwise
\item \texttt{"} Toggle string mode (push each character's ASCII value all the way up to the next ")
\item \texttt{:} Duplicate top stack value
\item \texttt{\textbackslash} Swap top stack values
\item \texttt{\$} Pop top of stack and discard
\item \texttt{.} Pop top of stack and output as integer
\item \texttt{,} Pop top of stack and output as ASCII character
\item \texttt{\#} Bridge: jump over next command in the current direction of the current PC
\item \texttt{g} A "get" call (a way to retrieve data in storage). Pop two values y and x, then push the ASCII value of the character at that position in the program. If (x,y) is out of bounds, push 0
\item \texttt{p} A "put" call (a way to store a value for later use). Pop three values y, x and v, then change the character at the position (x,y) in the program to the character with ASCII value v
\item \texttt{\&} Get integer from user and push it
\item \texttt{\~{}} Get character from user and push it
\item \texttt{@} End program
\item \texttt{0}-\texttt{9} Push corresponding number onto the stack
\end{itemize}
\vspace{2mm}
Note that the \texttt{p} instruction allows us to write self-modifying code.
\vfill
\pagebreak
\problem{}
Write a program that prints \say{\texttt{Hello World}}.
\problem{}
Write a program that prints the alphabet
\problem{}
Write a program that generates a random sequence of numbers (\texttt{0}-\texttt{9}).
\vfill
\problem{}
Write a program that does not contain the string \say{\texttt{Hello World}}, \par
but writes that string somewhere inside its source.
\problem{}
Replace the \texttt{x}s in the following program
so that the loop runs forever. \par
Do not use any control-flow instructions
(\texttt{>}, \texttt{<}, \texttt{\textasciicircum{}}, \texttt{v}, \texttt{\_}, \texttt{|}, \texttt{\#}, or \texttt{?}) \par
\hint{
Start by replacing all the \texttt{x}s with spaces. \par
You may not need all the \texttt{x}s, feel free to use a smaller rectangle.
}
\vspace{2mm}
\begin{center}
\texttt{>xxxxxxxxv \\
x ~ ~ ~ ~x \\
x ~ ~ ~ ~x \\
x ~ ~ ~ ~x \\
x ~ ~ ~ ~x \\
x ~ ~ ~ ~x \\
x ~ ~ ~ ~x \\
x ~ ~ ~ ~x \\
\textasciicircum{}xxxxxxxx@
}
\end{center}
\begin{solution}
The intended solution is self-modifying code:
\begin{center}
\texttt{>69*6+97pv\\
p ~ ~ ~ ~8\\
7 ~ ~ ~ ~8\\
9 ~ ~ ~ ~*\\
* ~ ~ ~ ~0\\
8 ~ ~ ~ ~0\\
8 ~ ~ ~ ~p\\
\textasciicircum{}p00-2*88@
}
\end{center}
\end{solution}
\vfill
\problem{Bonus}
Write a quine. (i.e, write a program that outputs itself)
\begin{solution}
\texttt{01->1\# +\# :\# 0\# g\# ,\# :\# 5\# 8\# *\# 4\# +\# -\# \_@}
\end{solution}
\vfill
\pagebreak