Building a
Bullsh*t Language

#bullshitlanguage

Building a
Bullsh*t Language

#bullshitlanguage

AnnotationScript

Java annotations with a LISP

Demo time!

Jan Ouwens

 

│ EqualsVerifier │ jqno.nl │ jqno

#bullshitlanguage

Climate for developers            









Read more at jqno.nl/climate

Weird projects

Weird project: Vim

Weird project: Astérix

Weird project: Astérix

Weird project: Astérix

Weird project: Astérix

Weird project: Astérix

Weird project: Lego

Weird project: Lego

Weird project: Lego

Weird project: Lego

Weird project: Lego

Weird project: Lego

Weird project: Lego

Weird project: Parallel Java

Weird project: Parallel Java

Weird project: Parallel Java

Weird project: Parallel Java

Weird project: Parallel Java

Weird project: AnnotationScript


Let’s do the opposite!



no annotations → only annotations

Weird project: AnnotationScript


The weirdest yet!

WHY!?

Why not?

WHY!?

@Autowired
@Bean
@Column(name = "wat")
@Deprecated
@JsonAlias("whynot")
@PostMapping("/endpoint/wtf")
@Test
public void waitwhat() {}

WHY!?

WHY!?

WHY!?

WHY!?

I got excited with this one!

Also

No ChatGPT

Except for the final demo

AnnotationScript

is

a LISP

LISP

(LISP)

((LISP))

(((LISP)))

What’s a LISP?

  • Common Lisp
  • Scheme
  • Emacs
  • Racket
  • Clojure

Syntax

(define (fizzbuzz x y)
  (cond ((eq? (remainder x 15) 0) (display "FizzBuzz\n"))
        ((eq? (remainder x 3) 0) (display "Fizz\n"))
        ((eq? (remainder x 5) 0) (display "Buzz\n"))
        (else (display x) (display "\n")))

  (cond ((< x y) (fizzbuzz (+ x 1) y))
        (else ())))

(fizzbuzz 1 100)

Syntax

(+ x 10)

Syntax

(+ x 10)

(+ x (* 2 5))

The Power of LISP

(+ x 10)

(+ x (* 2 5))

((if #t + -) x 10)

((Parentheses))

if (this.getId().equals(that.getId()))
(if (= (getId this) (getId that)))

Recursion

public int sum(int n) {
    int result = 0;
    for (int i = 0; i < n; i++) {
        result += i;
    }
    return result;
}

Recursion

public int sum(int n) {
    if (n == 0) {
        return 0;
    }
    else {
        return n + sum(n - 1);
    }
}

Recursion

(define (sum n)
  (cond ((eq? n 0) 0)
        (else (+ n (sum (- n 1))))))

Stack overflow

Stack overflow

java.lang.StackOverflowError
        at java.base/java.util.Objects.hashCode(Objects.java:103)
        at io.vavr.collection.HashArrayMappedTrieModule$AbstractNode.get(HashArrayMappedTrie.java:235)
        at io.vavr.collection.HashMap.get(HashMap.java:615)
        at nl.jqno.annotationscript.language.Environment.lookupOption(Environment.java:16)
        at nl.jqno.annotationscript.language.Environment.lookup(Environment.java:20)
        at nl.jqno.annotationscript.language.Evaluator.evaluateSymbol(Evaluator.java:53)
        at nl.jqno.annotationscript.language.Evaluator.evaluate(Evaluator.java:21)
        at nl.jqno.annotationscript.language.Evaluator.evaluateProc(Evaluator.java:117)
        at nl.jqno.annotationscript.language.Evaluator.evaluate(Evaluator.java:45)
        at nl.jqno.annotationscript.language.Evaluator.lambda$4(Evaluator.java:121)
        at io.vavr.collection.Traversable.foldLeft(Traversable.java:493)
        at nl.jqno.annotationscript.language.Evaluator.evaluateProc(Evaluator.java:120)
        at nl.jqno.annotationscript.language.Evaluator.evaluate(Evaluator.java:45)
        at nl.jqno.annotationscript.language.Evaluator.lambda$0(Evaluator.java:76)
        at io.vavr.collection.Traversable.find(Traversable.java:458)
        at nl.jqno.annotationscript.language.Evaluator.evaluateCond(Evaluator.java:76)
        at nl.jqno.annotationscript.language.Evaluator.evaluate(Evaluator.java:33)

Stack overflow

(sum 4)
(+ 4 (sum 3))
(+ 4 (+ 3 (sum 2)))
(+ 4 (+ 3 (+ 2 (sum 1))))
(+ 4 (+ 3 (+ 2 (+ 1 (sum 0)))))
(+ 4 (+ 3 (+ 2 (+ 1 0))))
(+ 4 (+ 3 (+ 2 1)))
(+ 4 (+ 3 3))
(+ 4 6)
10

Tail call optimization

Let’s re-write

Tail call optimization

(define (sum n)
  (cond ((eq? n 0) 0)
        (else (+ n (sum (- n 1))))))

(sum 4)

↓

(define (sum n acc)
  (cond ((eq? n 0) acc)
        (else (sum (- n 1) (+ n acc)))))

(sum 4 0)

Tail call optimization

(sum 4)
(+ 4 (sum 3))
(+ 4 (+ 3 (sum 2)))
(+ 4 (+ 3 (+ 2 (sum 1))))
(+ 4 (+ 3 (+ 2 (+ 1 (sum 0)))))
(+ 4 (+ 3 (+ 2 (+ 1 0))))
(+ 4 (+ 3 (+ 2 1)))
(+ 4 (+ 3 3))
(+ 4 6)
10

Tail call optimization

(sum 4 0)
(sum (- 4 1) (+ 4 0))
(sum 3 4)
(sum (- 3 1) (+ 3 4))
(sum 2 7)
(sum (- 2 1) (+ 2 7))
(sum 1 9)
(sum (- 1 1) (+ 1 9))
(sum 0 10)
10

Recursion

What if…

recursion is not supported?

Recursion

Y Combinator

Y Combinator

(define Y
  (lambda (le)
    ((lambda (f) (f f))
     (lambda (f)
       (le (lambda (x) ((f f) x)))))))

Y Combinator

No reasonable person can understand this

But it works

Demo time!

Annotations

Why I don’t like them

Why I don’t like them

Checked at runtime





You have a nice, compiled, strongly-typed language underneath:

Why not use it!

Why I don’t like them

Weakly typed

@Autowired
@Bean
@Column(name = "wat")
@Deprecated
@JsonAlias("whynot")
@PostMapping("/endpoint/wtf")
@Test
public void waitwhat() {}

Why I don’t like them

Stringly typed

@PreAuthorize("isFullyAuthenticated")
@PreAuthorize("isFullyAuthenticated()")

Why I don’t like them

Hard to discover

Why I don’t like them

Hard to debug

public @interface GetMapping {
    /**
     * Alias for {@link RequestMapping#name}.
     */
    @AliasFor(annotation = RequestMapping.class)
    String name() default "";

    /**
     * Alias for {@link RequestMapping#value}.
     */
    @AliasFor(annotation = RequestMapping.class)
    String[] value() default {};

    // ...
}

Why I don’t like them

Slow

List<Class<?>> allTheClasses = scanTheClasspath();  // 👈 expensive!
for (Class<?> cls : allTheClasses) {
    for (Annotation a : cls.getAnnotations()) {
        Class<?> ann = a.getAnnotationType();
        if (ann.getName().equals("SpringBootApplication")) {
            // Start the container
        }
    }
}

Anyway

Annotations, first try

@Parenthesis("if", @Parenthesis("<", "x", "0"), "'a'", "'b'")

Annotations, first try

No nesting annotations!

Annotations, second try

@Open
@Symbol("if")
@Open@Symbol("<")@Symbol("x")@Symbol("0")@Close
@Symbol("'a'")
@Symbol("'b'")
@Close

Annotations, second try

Sure! I’ll group them for you

 

 

Open[] opens = { @Open, @Open };
Symbol[] symbols = { @Symbol("if"), @Symbol("x"), @Symbol("0"),
                     @Symbol("'a'"), @Symbol("'b'") };
Close[] closes = { @Close, @Close };

Annotations, third try

public @interface Syntax {}  // 👈🏻 smart-ass!

public @interface Open extends Syntax {}
public @interface Symbol extends Syntax {}
public @interface Close extends Syntax {}

Syntax[] code = { @Open, @Symbol("if"), @Open, @Symbol("<"),
                  @Symbol("x"), @Symbol("0"), @Close, @Symbol("'a'"),
                  @Symbol("'b'"), @Close };

Annotations, third try

No extending annotations!

Annotations, fourth and final try

@Zero("if")
@Zero(list={@One("<"), @One("x"), @One("0")})
@Zero("'a'")
@Zero("'b'")

Annotations, fourth and final try

I see no issue with that!

Make as many as you like!

🥱

@Zero to @Eleven

Map to AnnotationScript

(if (< x 0) "a" "b")

Map to AnnotationScript

(
  if
  (
    <
    x
    0)
  "a"
  "b"
)

Map to AnnotationScript

(
       if
           (
          <
          x
          0  )
       "a"
       "b"
)

Map to AnnotationScript


@Zero("if")
@Zero(list={
    @One("<"),
    @One("x"),
    @One("0")})
@Zero("'a'")
@Zero("'b'")
public static class First {}

Implementation

Implementing LISP

 

Implementing LISP

Using Peter Norvig’s blog post:

(How to Write a (Lisp) Interpreter (in Python)) 🔗

Architecture

Architecture

Tokenizer

Tokenizer

@Zero("if")
@Zero(list={
    @One("<"),
    @One("x"),
    @One("0")
})
@Zero("'a'")
@Zero("'b'")

Tokenizer

@Zero("if")       // 'if'
@Zero(list={      // '('
    @One("<"),    // '<'
    @One("x"),    // 'x'
    @One("0")     // '0'
})                // ')'
@Zero("'a'")      // 'a'
@Zero("'b'")      // 'b'

DONE! 🥳

Architecture

Parser

Parser

  • Atoms (0, 'a') remain the same
  • Symbols (define, if, <) are wrapped in Symbol class
  • ( starts a sub-list
  • ) ends a sub-list
List<Object> ast = List.of(
    Symbol("if"),
    List.of(Symbol("<"), Symbol("x"), 0),
    "a",
    "b");

Architecture

Environment

Environment

(define x 10)

Environment

(define x 10)

Architecture

Evaluator

Evaluator

Is it an Atom?
0, 'a'

↓

Return it

Evaluator

Is it a Symbol?
if, <

↓

Look up in Environment
Return it

Evaluator

Is it a List?
(< x 0)

↓

Evaluate all elements
Call function
Return result

Tail call optimization

Evaluator works recursively

stack overflow after ~60

Tail call optimization

Use Peter Norvig’s second blog post:

(An ((Even Better) Lisp) Interpreter (in Python)) 🔗

Tail call optimization

  • Add mutability
  • Evaluate procedure calls in-place

Tail call optimization

Instead of this:

public Object evaluate(Object expression) {
    // ...
    if (isAtom(expression)) {
        return evaluateAtom(expression);
    }
    if (isProc(expression)) {
        var evaluated = evaluateProc(expression);
        return evaluate(evaluated); // 👈 recursive call
    }
}

Tail call optimization

We do this:

public Object evaluate(Object expression) {
    var exp = expression;
    while (true) {
        // ...
        if (isAtom(exp)) {
            return evaluateAtom(expression);
        }
        if (isProc(exp)) {
            exp = evaluateProc(exp); // 👈 loop
        }
    }
}

Tail call optimization

No more stack overflow 🥳

Interlude

Code sample

@Zero("begin")
@Zero(list={@One("define"), @One("fizz-buzz"), @One(list={@Two("lambda"),
  @Two(list=@Three("n")), @Two(list={@Three("cond"),
    @Three(list={@Four("="), @Four(list={@Five("%"), @Five("n"),
      @Five("15")}), @Four("0")}), @Three("'fizzbuzz'"),
    @Three(list={@Four("="), @Four(list={@Five("%"), @Five("n"),
      @Five("3")}), @Four("0")}), @Three("'fizz'"),
    @Three(list={@Four("="), @Four(list={@Five("%"), @Five("n"),
      @Five("5")}), @Four("0")}), @Three("'buzz'"),
    @Three("else"), @Three("n")})})})
@Zero(list={@One("map"), @One("println"), @One(list={@Two("map"),
  @Two("fizz-buzz"), @Two(list={@Three("range"),
  @Three("1"), @Three("101")})})})
public class FizzBuzz {}

Ain’t nobody got no time for that

Write normal LISP


  (begin
    (define fizz-buzz (lambda (n)
      (cond (= (% n 15) 0) 'fizzbuzz')
      (cond (= (% n 3) 0) 'fizz')
      (cond (= (% n 5) 0) 'buzz')
      (else n))
    (map println (map fizz-buzz (range 1 101))))

Wrap it

String code = """
  (begin
    (define fizz-buzz (lambda (n)
      (cond (= (% n 15) 0) 'fizzbuzz')
      (cond (= (% n 3) 0) 'fizz')
      (cond (= (% n 5) 0) 'buzz')
      (else n))
    (map println (map fizz-buzz (range 1 101))))""";

Tokenizer

String code = """
  (begin
    (define fizz-buzz (lambda (n)
      (cond (= (% n 15) 0) 'fizzbuzz')
      (cond (= (% n 3) 0) 'fizz')
      (cond (= (% n 5) 0) 'buzz')
      (else n))
    (map println (map fizz-buzz (range 1 101))))""";

return code
    .replace("(", " ( ")
    .replace(")", " ) ")

Tokenizer

String code = """
  (begin
    (define fizz-buzz (lambda (n)
      (cond (= (% n 15) 0) 'fizzbuzz')
      (cond (= (% n 3) 0) 'fizz')
      (cond (= (% n 5) 0) 'buzz')
      (else n))
    (map println (map fizz-buzz (range 1 101))))""";

return code
    .replace("(", " ( ")
    .replace(")", " ) ")
    .split(" ");

Code generator

(recurse

MetaScript

Demo time!

Architecture

Tokenizer

Tokenizer

  • Unit tests written in Java, not AnnotationScript

  • AnnotationScript evaluates to regular Java objects

Tokenizer

Unit tests: identical!

MetaScript

Parser

Parser

Unit tests: identical!

MetaScript

Evaluator

Evaluator

Recursion issue

(define (sum
  (lambda (i)
    (cond
      ((eq? i 0) 0)
      (else
        (+ i (sum (sub1 i)))))))

  (sum 4))

Recursion issue

(define (sum
  (lambda (i)
    (cond
      ((eq? i 0) 0)
      (else
        (+ i (sum (sub1 i)))))))

  (sum 4))

cond has no true branch

Recursion issue

(define (sum
  (lambda (i)
    (cond
      ((eq? i 0) 0)
      (else
        (+ i (sum (sub1 i)))))))

  (sum 4))

Invalid identifier: sum

Recursion issue

(define (sum
  (lambda (i)
    (cond
      ((eq? i 0) 0)
      (else
        (+ i (sum (sub1 i)))))))

  (sum 4))

Y Combinator ???

Recursion issue

(define (sum
  (lambda (i recurse)
    (cond
      ((eq? i 0) 0)
      (else
        (+ i (recurse (sub1 i) recurse))))))

  (sum 4 sum))

Solution: function is parameter to itself

(recurse

Turing complete

I promised

But how to prove it?

Turing complete

  • Can solve any computable problem
  • Need loops, if, IO
  • Mathematical proof is hard and boring

Turing machine

Turing machine

  • Turing complete by definition
  • Tape with cells
  • Operations: read at head, write at head, move head

Turing machine

Implement one!

…

Brainfuck!

Demo time!



brainfuck generator 🔗

))

What’s next

Did it escalate?

Error handling

cond has no true branch

“[It] expects the programmer to be perfect”

String.split

"'Hello world'" → "'Hello" + "world'"

Spring integration

🤪

Conclusion

Conclusion

Learn about annotations

Conclusion

Learn about LISP

Conclusion

It was fun

Conclusion

Greenspun’s Tenth Rule:

Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp.

Questions?

#bullshitlanguage

Fin

Image credits

annotationscript by moinart on Fiverr
architecture-1 by Jan Ouwens
architecture-2 by Jan Ouwens
background by Jan Ouwens
bored by DreamStudio (Stable Diffusion) with prompt “Nerd behind laptop looking bored. Many Salvador Dali melting clocks.”
climate-change by DreamStudio (Stable Diffusion) with prompt “Laptop with image of a coal plant emitting thick black smoke. It’s on a table next to a pile of books and a coffee cup. In the background lush springtime forest”
code-generator by DreamStudio (Stable Diffusion) with prompt “Monkey typing at a computer”
comics-0 by Jan Ouwens - picture of “Asterix de Galliër” by René Goscinny & Albert Uderzo
comics-1 by Jan Ouwens - picture of a stack of comic books with on top: “Asterix de Galliër” by René Goscinny & Albert Uderzo
comics-2 by Jan Ouwens - picture of a stack of comic books with on top: “Gilles de Geus - De Spaanse furie” by Hanco Kolk
comics-3 by Jan Ouwens
comics-4 by Jan Ouwens - picture of two comic books: “Astérix Légionnaire” by René Goscinny & Albert Uderzo, and “Gilles de Geus - De revue” by Hanco Kolk & Peter de Wit
discoverability Screenshot from IntelliJ IDEA, taken by Jan Ouwens
duke-says-no by Jeff Dinkins for Sun/Oracle - source
duke-says-yes & duke-says-yes-background by Jeff Dinkins for Sun/Oracle - source
environment-1 by Jan Ouwens
environment-2 by Jan Ouwens
escalation by DreamStudio (Stable Diffusion) with prompt “A tsunami of snow coming from a mountain, a person running away from it, powdered snow in the air”
evaluator by Jan Ouwens
fun by dreamstudio (stable diffusion) with prompt “childrens drawing of stick fligure children playing in a school playground with a swing, a slide and a tree”
hackernews Screenshot from Hacker News, taken by Jan Ouwens on 2023-09-11
jan-ouwens by Riemke Ouwens
lego-0 by Jan Ouwens
lego-1 by Jan Ouwens
lego-2 by Jan Ouwens
lego-3 by Jan Ouwens
lego-4 Screenshot from my website, taken by Jan Ouwens on 2023-09-30
lego-5 Screenshot from Rebrickable, taken by Jan Ouwens on 2023-09-29
lego-6 by Jan Ouwens
lockdown by DreamStudio (Stable Diffusion) with prompt “fat nerdy person at computer. man cave. messy room with parcels, stacks of books, empty pizza boxes, gadgets”
meta-evaluator & meta-parser & meta-tokenizer by Jan Ouwens
mind-blown-1 by DreamStudio (Stable Diffusion) with prompt “Person looking at a computer screen, very surprised, wide eyes, open mouth”
mind-blown-2 by DreamStudio (Stable Diffusion) with prompt “Person looking at a computer screen, very surprised, wide eyes, open mouth”
nerd-cred by DreamStudio (Stable Diffusion) with prompt “Rap music album cover in the style of Eminem, 50ct and notorious BIG. Photograph one face of fat, white, nerdy guy with large beard, messy hair, jewelry and colored glasses. Fish eye lens. Album title”nerd cred” appears next to face”
paralleljava-0 by Jan Ouwens
paralleljava-1 by Jan Ouwens
paralleljava-2 Screenshot from GitHub taken by Jan Ouwens on 2023-09-29
paralleljava-3 Screenshot from Todo-Backend taken by Jan Ouwens
paralleljava-4 by J-Fall - source
parser by Jan Ouwens
rite-of-passage by DreamStudio (Stable Diffusion) with prompt “Graduation ceremony. Fat nerdy man with glasses and unkempt beard on stage.”
stackoverflow Screenshot from StackOverflow, taken by Jan Ouwens on 2023-09-11
the-little-schemer by MIT Press - source
tokenizer by Jan Ouwens
turing-machine by DreamStudio (Stable Diffusion) with prompt “A sewing machine sewing a long, straight, white ribbon that must not be bundled up”
vim by Jan Ouwens



Enterprise Lego model designed by MiniTrekMocs


No animals were harmed during the making of this slide deck.
Except bugs. Bugs were squashed without hesitation.