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RASEL (Random Access Stack Esoteric Language) v2

A programming language inspired by Befunge where instead of the program space random access you have the ability to swap with the Nth value in the stack.

This repository includes specification, examples, executables and library, its tests running as GitHub Action. There is also an IDE -- read more about it in the Esolang Wiki RASEL language article.

Usage

Install

gem install rasel

Run

To run a program you can either use the executable and pass a source file as argument:

$ echo '"olleh",,,,,A,@' > temp.rasel
$ rasel temp.rasel

Or pipe the source code directly:

$ echo '"olleh",,,,,A,@' | rasel

Or pass it as a String arg in Ruby runtime:

require "rasel"
puts RASEL('"olleh",,,,,@').stdout.string

To run a program and feed it some stdin you can either put it to a file:

$ rasel my_program.rasel < my_input.txt

Or pipe it too:

$ echo 5 | rasel examples/factorial.rasel
$ echo 5 | rasel examples/fibonacci.rasel

Reference specification

• Every "error raised" in this specification mean it should halt the program with any (depends on the implementation) exit status code from 1 to 255. The only currently known undefined things are how float numbers are printed (TODO: maybe implement the ability to specify precision?) and how empty source file is treated. If you find anything else missing, please report.
• Programs are read as ASCII-8BIT lines splitted by 0x0A character. For every source code line trailing space characters are trimmed and then readded to reach the length defined by the highest x coordinate of any (including invalid) non-space character in the whole source file. Lines with no non-space characters at the end of the source file are trimmed. After the source code load the program space is effectively a rectangle of NxM characters that has at least one non-space character in the last column and in the last row. Space characters are nops when not in the "stringmode". All other characters that are not defined in the specification raise an error if the instruction pointer reaches them unless the previous instruction was "trampoline" so it's just skipped.
• Stack data type is Rational. Numerators and denominators are bignums, i.e. there should be no rounding errors. The "is integer" in this specification means "does not have a fractional part".
• "Popping a value" means taking out the top value from the stack and using it in the instruction that initiated the popping. When stack is empty popping from it creates 0. For language user it should be effectively indistinguishable if the stack is empty or just has several 0 left in it.
• Instructions:
  • @ -- exit with code popped from the stack
    If the value isn't integer and isn't within 0..255 the error is raised.
  • 0..9, A..Z -- push single Base36 digit value onto the stack
  • : -- "duplicate" -- pop a value and add it back to the stack twice
  • >, <, ^, v -- set instruction pointer direction
  • " -- toggle "stringmode" (by default is off)
    In this mode all instruction and invalid (i.e. having no meaning as an instruction) characters are pushed onto the stack as a corresponding number from ASCII table.
    In this mode space character (that is nop by default) is treated as an instruction to push the value 32 onto the stack.
  • # -- "trampoline" -- the character under the next instruction pointer position will be ignored
    If it's the last character on the source code line the first character on the other side of the line will be skipped.
    If it's the last instruction on the source code line but not the last character (i.e. there are spaces or invalid characters filling it to the edge of the program space rectangle) the next character will the ignored, not from the other side of the rectangle.
    Same about source code columns and in both directions.
  • \ -- "swapn" -- pop a value N from the stack, then swap the next one with the N+1th
    If N isn't an integer the error is raised.
    If N is 0 or negative then nothing swaps and it's effectively the same as $.
    If N exceeds the current depth of the stack then the stack is extended with zeros as much as needed.
  • -, /, % -- pop two values and push the result of an arithmetic operation
    If divisor or modulus is 0 it's not an error and result is 0.
  • . -- pop a value and print it as a number
    Print as an integer or as a float if there is a fractional part.
  • , -- pop a value and print it as a corresponding ASCII char
    If the value isn't an integer within 0..255 the error is raised.
  • ~ -- read character from STDIN, put its ASCII code onto the stack and work as "trampoline" unless EOF
    EOF does not put anything onto the stack.
  • & -- read Base10 non-negative integer from STDIN, put it onto the stack and work as "trampoline" unless EOF
    EOF does not put anything onto the stack.
    Leading non-digit characters are omitted -- that allows to consecutively read numbers that have any non-digits characters in between.
  • j -- "jump forward" -- pop a value from the stack and jump over that many cells in the current instruction pointer direction
    If the value isn't integer the error is raised.
    If the value is negative, jump is done the opposite direction but the instruction pointer direction does not change.
  • ? -- "if positive" -- pop a value and work as "trampoline" if it's positive

Not all but the main differences from Befunge-93/98

• stack and program space ("playfield" in Befunge-93 terminology) have no size limits
• stack data type is Rational
• instructions that are added
  • A..Z (case sensitive Base36)
    push an integer from 10 to 35 onto the stack
  • j ("jump forward" from Funge-98)
• instruction \ ("swapn" -- the Random Access thing) pop a value N from the stack and swap the next one with the N+1th
• instructions | and _ are replaced with a single instruction ? that tests if the value is positive
• instructions that are removed
  • ? (move to a random direction)
  • $ for arbitrary value can be replaced with :--, 0/- or ? (are there any more ways?)
  • + and * (addition and multiplication)
    can be easily emulated using - and / (subtraction and division), removed just for the fun of it
  • ` and ! ("if greater" and "logical negation")
    can be easily emulated using other instructions
  • p and g (put and get)
    random stack access makes self-modification almost useless and simplifies the implementation because the program space won't expand, also it might be easier for optimization

Examples (more here)

Factorial(n) (OEIS A000142)

1&\:?v:1-3\-/
1\/.@>-1

Fibonacci(n) (OEIS A000045)

1&-:?v1\:3\01\--1\
2\.@ >

Project Euler's Problem 1 "Multiples of 3 and 5"

&>:?v1-::3%1\5%/ ?v
 ^  >--.@j5\1--\3:<

Note that in the examples folder the PE solutions might assume the \n-terminated input, not the chomped one like AoC website gives it to you.

Prime numbers generator (OEIS A000040) (trial division by a growing list)

2:4v     >-       2-\:--:.>01--#
   >::\:?^:3\1\%?v2-\1\:2\ 01--
                 >2-\:--  v

$ rasel examples/prime.rasel
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 ... ^C

Advent of Code 2020 1 1 solution

Befunge-93 (by @fis):

1+:#v&\fp
   0>$1-:00p>:#v_00g
               >:fg00gfg+'-:*5--#v_fg00gfg*.@
            ^                  -1<

RASEL:

&v
 >2v         >///-
   >01--::\:?^:0:5\:6\---K/"e"-:/?v1\1-\
                                  >1:4\//.A,@

Here you can see that it's about the same size.

IDE and other executables

The "RASEL IDE" is for editing the .rasela "annotated" code. It is fully explained in the Esolang Wiki article.

• bin/rasel-convert

  $ rasel-convert 
  usage:
          $ rasel-convert <file.rasel> <file.rasela>
          $ rasel-convert <file.rasela> <file.rasel>
  

  The .rasela file format is JSON.
• bin/rasel-annotated
  Use it to run .rasela. Currently it has some time and stdout print size limits because you don't want to wait forever when launching via the IDE. Use env var IDE_LIMIT_PRINTED to override the default print size limit of 500000.
• bin/rasel-ide

  $ rasel-ide
  usage:	rasel-ide <file.rasela>
  

  CSS and JS improvements ideas and help are welcome.

Specification version history

• v0
• v1 introduced \ ("swapn")
• v2 deprecated $ ("discard")

Note that the gem version number isn't supposed to match the specification version number.

TODO

• some examples
• gemify
• page at esolangs.org
• announce
• minimal instruction set enough for random write
• specification implementation, tests and docs
  • non-instructional
  • instructional
    • old
      • ", #
      • 0..9
      • :, \
      • >, <, ^, v
      • -, /, %
      • ., ,
    • changed
      • @
      • ~, &
      • ?
      • \
    • new
      • A..Z
      • j
      • something about additional stacks?
• other tests
  • bin
    • bin/rasel
    • bin/rasel-annotated
      • basic
      • the rest
    • bin/rasel-convert
    • bin/rasel-ide?
  • add truffleruby (use https://github.com/graalvm/container/pkgs/container/truffleruby)
  • add jruby (JAVA_HOME=$(/usr/libexec/java_home) ruby test.rb)
• IDE improvements
  • more compact JSON export
  • scrollable div for log
  • highlight the cell on log mouse hover
  • easier clearing the cell
  • navigate with keyboard arrows
  • add/remove cell in one row
  • copy/paste rows
  • show accumulated prints
  • undo(/redo?)
  • \ should annotate right one, not left one?
  • colorful annotations?
  • annotate empty cell to annotate top?
  • configurable print size and time limits?
  • print Rationals

Development notes

TODO: add a tutorial how to debug with rasel-annotated