Initial summary of HLL ideas from uni.org

doc/notes-on-hll.md

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+## Syntax
+
+Just a sketch, at the moment. The connection between Racket `expr`s
+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 ...))