Table of Contents
The HipHop Programming Language
HipHop is a synchronous programming language. It supports sequence, parallelism, preemption, instantaneous communication between components by the means of signals, and it is deterministic.
A HipHop program executes by reacting to external events. Each of these executions is called a reaction or an instant. It is the role of JavaScript to decide when a HipHop program should execute its next instant.
During a HipHop reaction, all components see the very same information. For instance, all compoments share the same information about signals that have been emitted or not. Programs are to be causal. That is:
- programs have only one possible unambigious execution path and during;
- programs cannot contradict themselves during a reaction, that is, they can perform an action that contradict a decision already take during the reaction;
- programs cannot take decision based on action not already executed during the reaction;
- programs cannot execute infinite loop during a reaction.
Programs that do not respect these four rules are rejected, either statically or dynamically. See the section Errors for examples of incorrect programs.
HipHop and JavaScript cooperate all along the execution. The program always starts as a regular JavaScript program, which is in charge of constructing the HipHop program and triggering its reaction.
During the reaction, JavaScript is used to evaluate the HipHop predicates
and to compute the values associated with signals. JavaScript can
be notified of HipHop signal emission by attaching listeners to a
reaction machine. These listeners are invoked for each output signals
(thoses declared with the out keyword) at the end of the reaction.
Syntax and JavaScript embedding
HipHop requires the program to use ECMAScript modules.
The HipHop syntax extends the JavaScript syntax with one single statement:
hiphop <HHstatement>The hiphop tag is to be followd by a HipHop statement, whose
syntax is described in this bnf grammar.
This chapter documents the HipHop programming language. The connection with JavaScript is described in chapter api and the standard HipHop modules are described in chapter standard modules.
Example
import * as hh from "@hop/hiphop";
const prg = hiphop module() {
in A; in B; in R; out O;
do {
fork {
await (A.now);
} par {
await (B.now);
}
emit O();
} every (R.now)
}
export const mach = new hh.ReactiveMachine(prg, "ABRO");