diff --git a/src/common/ecs/compiler.ts b/src/common/ecs/compiler.ts
index d3ddbd98..64e912ec 100644
--- a/src/common/ecs/compiler.ts
+++ b/src/common/ecs/compiler.ts
@@ -338,6 +338,7 @@ export class ECSCompiler extends Tokenizer {
             if (cmd == 'comment') {
                 this.expectTokenTypes([ECSTokenType.CodeFragment]);
             }
+            // TODO: need to make these local names, otherwise we get "duplicate name"
             if (cmd == 'system') {
                 let sys = this.annotate(() => this.parseSystem());
                 this.em.defineSystem(sys);
@@ -350,7 +351,13 @@ export class ECSCompiler extends Tokenizer {
 
     parseScopeUsing() {
         let instlist = this.parseList(this.parseSystemInstanceRef, ',');
+        let params = {};
+        if (this.peekToken().str == 'with') {
+            this.consumeToken();
+            params = this.parseSystemInstanceParameters();
+        }
         for (let inst of instlist) {
+            inst.params = params;
             this.currentScope?.newSystemInstance(inst);
         }
     }
@@ -464,10 +471,6 @@ export class ECSCompiler extends Tokenizer {
         let system = this.em.getSystemByName(name);
         if (!system) this.compileError(`I couldn't find a system named "${name}".`, this.lasttoken.$loc);
         let params = {};
-        if (this.peekToken().str == 'with') {
-            this.consumeToken();
-            params = this.parseSystemInstanceParameters();
-        }
         let inst = { system, params, id: 0 };
         return inst;
     }
@@ -475,6 +478,9 @@ export class ECSCompiler extends Tokenizer {
     parseSystemInstanceParameters() : SystemInstanceParameters {
         let scope = this.currentScope;
         if (scope == null) throw new Error();
+        if (this.peekToken().str == '[') {
+            return { query: this.parseQuery() };
+        }
         this.expectToken('#');
         let entname = this.expectIdent();
         this.expectToken('.');
diff --git a/src/common/ecs/ecs.ts b/src/common/ecs/ecs.ts
index 2b50c45a..1129251f 100644
--- a/src/common/ecs/ecs.ts
+++ b/src/common/ecs/ecs.ts
@@ -61,6 +61,7 @@ export interface System extends SourceLocated {
 }
 
 export interface SystemInstanceParameters {
+    query?: Query;
     refEntity?: Entity;
     refField?: ComponentFieldPair;
 }
@@ -600,6 +601,8 @@ class ActionEval {
                 this.qr = this.qr.intersection(new EntitySet(scope, rq));
                 //console.log('with', instance.params, rq, this.qr);
             }
+        } else if (instance.params.query) {
+            this.qr = this.qr.intersection(new EntitySet(scope, instance.params.query));
         }
         this.entities = this.qr.entities;
         //let query = (this.action as ActionWithQuery).query;
@@ -767,10 +770,18 @@ class ActionEval {
     }
     __data(args: string[]) {
         let { component, field, bitofs } = this.parseFieldArgs(args);
-        if (this.qr.entities.length != 1) throw new ECSError(`data command operates on exactly one entity`); // TODO?
+        if (this.qr.entities.length != 1) throw new ECSError(`data operates on exactly one entity`, this.action); // TODO?
         let eid = this.qr.entities[0].id; // TODO?
         return this.dialect.datasymbol(component, field, eid, bitofs);
     }
+    __const(args: string[]) {
+        let { component, field, bitofs } = this.parseFieldArgs(args);
+        if (this.qr.entities.length != 1) throw new ECSError(`const operates on exactly one entity`, this.action); // TODO?
+        let constVal = this.qr.entities[0].consts[mksymbol(component, field.name)];
+        if (constVal === undefined)  throw new ECSError(`field is not constant`, this.action); // TODO?
+        if (typeof constVal !== 'number')  throw new ECSError(`field is not numeric`, this.action); // TODO?
+        return constVal << bitofs;
+    }
     __index(args: string[]) {
         // TODO: check select type and if we actually have an index...
         let ident = args[0];