Add syntax for sync. Closes #6

packages/compiler/src/compiler/codegen.ts

@@ -328,6 +328,8 @@ ${joinItems(sa.captureBinders.map(binderTypeGuard(t)), '\n')}
 
     x(ctx.parser.stopStatement, (s, t) => t`${terminalWrap(t, s.facetToStop, s.body)};`);
 
+    xf(ctx.parser.syncStatement, (s, t) => t`_sync(${walk(s.peerToSyncWith)}, __SYNDICATE__.Turn.ref({ message() {${walk(s.body)}} }));`);
+
     return tree;
 }
 

packages/compiler/src/compiler/grammar.ts

@@ -57,6 +57,10 @@ export interface StopStatement extends StatementTurnAction {
     facetToStop: FacetToStop;
 }
 
+export interface SyncStatement extends StatementTurnAction {
+    peerToSyncWith: Expr;
+}
+
 export interface GenericEventEndpointStatement extends StatementTurnAction {
     facetToStop: FacetToStop | 'none' | 'once-wrapper';
     once: boolean;
@@ -385,6 +389,15 @@ export class SyndicateParser {
                        alt(this.block(o.body), this.statementBoundary));
         });
 
+    // Principal: Turn
+    readonly syncStatement: Pattern<SyncStatement> =
+        this.turnAction(o => {
+            o.body = [];
+            return seq(atom('sync'),
+                       map(this.expr1(), e => o.peerToSyncWith = e),
+                       this.block(o.body));
+        });
+
     // Principal: none
     readonly atStatement: Pattern<AtStatement> =
         scope(o => {

packages/compiler/test/compiler.test.ts

@@ -46,6 +46,21 @@ __SYNDICATE__.Turn.active.facet(() => {
 
 });
 
+describe('sync', () => {
+    it('empty body', () => expectCodeEqual(`sync p {}`, `
+__SYNDICATE__.Turn.active._sync(p, __SYNDICATE__.Turn.ref({
+    message() {}
+}));`));
+
+    it('nonempty body', () => expectCodeEqual(`sync p {q(); r();}`, `
+__SYNDICATE__.Turn.active._sync(p, __SYNDICATE__.Turn.ref({
+    message() {
+        q();
+        r();
+    }
+}));`));
+});
+
 describe('spawn', () => {
 
     it('without name', () => expectCodeEqual(`spawn { a; b; c; }`, `