Ceylon comprehension compilation for the Java platform as I understand it

explanation.md

Take this Ceylon code:

{ for (x in foo) if (bar) for (y in baz) op(x, y) }

The compiler generates an anonymous AbstractIterable class for this with a chain of boolean "has thing" methods:

• next() (the only non-boolean method) calls y() to get the next element, if possible
• y() checks $iterator$2 to request an iterator for baz, then gets the next item – if it exists, y is set, else y$exhausted$ is set
• $iterator$2() checks if the x iterator isn’t exhausted, if the y iterator exists and if it doesn’t, checks $next$1() to see if it should generate another iterator
• $next$1() checks x() to see if it should even check the expression, then checks the expression (I abbreviated it below to bar)
• x() checks if the "root" iterator isn’t exhausted, and sets x in that case

result.java

/** see the full version in test/src/com/redhat/ceylon/compiler/java/test/expression/comprehensions/for_if_for.src */
new AbstractIterator(){
    {
        $iterator$0 = foo.iterator();
    }
    private final Iterator $iterator$0;
    private Integer x;
    private boolean x$exhausted$;
    
    private final boolean x() {
        final Object $ceylontmp$item$0 = $iterator$0.next();
        x$exhausted$ = $ceylontmp$item$0 == finished;
        if (x$exhausted$) {
            return false;
        } else {
            x = $ceylontmp$item$0;
            return true;
        }
    }
    
    private final boolean $next$1() {
        while (true) {
            if (!this.x()) break;
            if (bar) {
                break;
            }
        }
        return !x$exhausted$;
    }
    private Iterator $iterator$2;
    
    private final boolean $iterator$2() {
        if (x$exhausted$) return false;
        if ($iterator$2 != null) return true;
        if (!this.$next$1()) return false;
        $iterator$2 = baz.iterator();
        return true;
    }
    private Integer y;
    private boolean y$exhausted$;
    
    private final boolean y() {
        while (this.$iterator$2()) {
            final Object $ceylontmp$item$1 = $iterator$2.next();
            y$exhausted$ = $ceylontmp$item$1 == finished;
            if (y$exhausted$) {
                $iterator$2 = null;
            } else {
                y = $ceylontmp$item$1;
                return true;
            }
        }
        if (x$exhausted$) y$exhausted$ = true;
        return false;
    }
    
    public final Object next() {
        if (this.y()) {
            final Integer x = this.x;
            final Integer y = this.y;
            return op(x, y);
        } else return finished;
    }

(read result.java from bottom to top)