cmd

Scheme Transpiler

This transpiles the input message to Scheme. Run with:

go run main.go INPUT_FILE EXPRESSION

This outputs Scheme program, so you can pipe to, for example, gosh to evaluate and print out the evaluation result of the EXPRESSION.

Checkerboard example

https://message-from-space.readthedocs.io/en/latest/message33.html

See checkerboard.input. There's the checkerboard definition. According to the interpretation on the page above, this takes two numbers as arguments:

go run main.go ./checkerboard.input "ap ap checkerboard 7 0"

This command outputs Scheme program that evaluates "ap ap checkerboard 7 0" and pass the result to printout in the prelude.scm. Currently, the printout command is defined as (print (serialize x)). The serialize function takes a value from the evaluator and creates a scheme world's value like this:

((0 . 0) (0 . 2) (0 . 4) (0 . 6) (1 . 1) (1 . 3) (1 . 5) (2 . 0) (2 . 2)
 (2 . 4) (2 . 6) (3 . 1) (3 . 3) (3 . 5) (4 . 0) (4 . 2) (4 . 4) (4 . 6)
 (5 . 1) (5 . 3) (5 . 5) (6 . 0) (6 . 2) (6 . 4) (6 . 6))

(This is a list of pixel positions to draw a checkerboard image.)

Galaxy output

$REPO_ROOT/messages/galaxy.txt is a huge input that defines a galaxy function. This function takes two values: a state and a coordinate. Per https://message-from-space.readthedocs.io/en/latest/message39.html, the state starts from nil and the coordinate starts from (0 . 0):

go run main.go ../../../messages/galaxy.txt "ap ap galaxy nil ap ap cons 0 0"

This outputs a tuple of three (or two) elements:

(
  0
  (0 (0) 0 ())
  (((-1 . -3) ...) ((-7 . -3) (-8 . -2)) ()))

The first element is 0 or 1. If it's 0, it's a draw instruction. If it's 1, it's a send instruction. So far, we haven't seen a send instruction, so we ignore that.

The second element is the next state (e.g. the argument that we places nil for this run). The third element is a list of draw instruction like we saw in the checkerboard example above. Note that this contains multiple images. In this case, the first image has a dot at the coordinate (-1, -3) etc., the second image has a coordinate (-7, -3) etc., and the last image doesn't have any dot.

As we saw, the next state (0 (0) 0 ()) is given, so we can run this iteratively:

go run main.go ../../../messages/galaxy.txt \
    "ap ap galaxy
        ap ap cons
           0
           ap ap cons
              ap ap cons 0 nil
              ap ap cons
                 0
                 ap ap cons nil nil
        ap ap cons 0 0"

 (Formatted to make the argument understandable)

This process repeats to some extent. See the shared notes for details.

draw.py

It's hard to render the images by hand. draw.py renders the image by taking an output of galaxy.txt runs.