syndicate-2017/doc/notes-on-hll.md

Syntax

Just a sketch, at the moment. The connection between Racket exprs and I needs to be clarified, among many other things.

Instantaneous actions, I := (actor Idef ...)
						    (state [O ...] [E I ...] ...)
							(background I ...)
							(assert! P)
							(retract! P)
							(send! P)
							(flush!)              ;; ???
							(begin I ...)         ;; and, generally, expr?
  Actor-level defs, Idef := I
							(define id expr)
							(define (id id ...) expr ...)
	  Ongoing actions, O := (on E I ...)
							(once E I ...)
							(assert P)
							(track [x Agg] I ...)
							(begin O ...)         ;; ??? expr?
		Predicates, Pred := (not Pred)
							(exists P Pred)
							(forall P Pred)
							expr
			   Events, E := (asserted P)
							(retracted P)
							(message P)
							(rising-edge Pred)
							(falling-edge Pred)
         Aggregates, Agg := (count expr P)
		                    (set expr P)
							(hash k_expr v_expr P)
							(project P)
							(single-value expr P)
							(single-value expr P #:default def_expr)
							Pred
             Patterns, P := ... ;; uses $var as binder

(define-syntax-rule (until E O ...)
  (state [O ...] [E]))

(define-syntax-rule (forever O ...)
  (until (rising-edge #f) O ...))

Examples

#lang prospect/actor
;; Simple mutable box and count-to-infinity box client.

(struct set-box (new-value) #:transparent)
(struct box-state (value) #:transparent)

(actor (forever #:collect [(value 0)]
         (assert (box-state value))
         (on (message (set-box $new-value))
           new-value)))

(actor (forever
         (on (asserted (box-state $value))
           (send! (set-box (+ value 1))))))