diff --git a/src/common/ecs/compiler.ts b/src/common/ecs/compiler.ts
index 122cce35..3e452930 100644
--- a/src/common/ecs/compiler.ts
+++ b/src/common/ecs/compiler.ts
@@ -2,7 +2,7 @@
 import { mergeLocs, Tokenizer, TokenType } from "../tokenizer";
 import { SourceLocated } from "../workertypes";
 import { newDecoder } from "./decoder";
-import { Action, ArrayType, ComponentType, DataField, DataType, DataValue, ECSError, Entity, EntityArchetype, EntityManager, EntityScope, IntType, Query, RefType, SelectType, SourceFileExport, System } from "./ecs";
+import { Action, ArrayType, ComponentType, DataField, DataType, DataValue, ECSError, Entity, EntityArchetype, EntityManager, EntityScope, IntType, Query, RefType, SelectType, SELECT_TYPE, SourceFileExport, System } from "./ecs";
 
 export enum ECSTokenType {
     Ellipsis = 'ellipsis',
@@ -15,6 +15,7 @@ export enum ECSTokenType {
 export class ECSCompiler extends Tokenizer {
 
     currentScope: EntityScope | null = null;
+    debuginfo = false;
 
     constructor(
         public readonly em: EntityManager)
@@ -63,6 +64,7 @@ export class ECSCompiler extends Tokenizer {
             if (!text) this.compileError(`I can't find the import file "${path}".`);
             this.em.imported[path] = true;
             let comp = new ECSCompiler(this.em);
+            comp.debuginfo = this.debuginfo; // TODO: clone compiler
             try {
                 comp.parseFile(text, path);
             } catch (e) {
@@ -224,11 +226,12 @@ export class ECSCompiler extends Tokenizer {
         // TODO: unused events?
         let event = this.expectIdent().str;
         this.expectToken('do');
-        let select = this.expectTokens(
-            ['once', 'foreach', 'join', 'with', 'if', 'select']).str as SelectType; // TODO: type check?
+        let select = this.expectTokens(SELECT_TYPE).str as SelectType; // TODO: type check?
         let query = undefined;
         let join = undefined;
-        if (select != 'once') {
+        if (select == 'once') {
+            if (this.peekToken().str == '[') this.compileError(`A "${select}" query can't include a query.`)
+        } else {
             query = this.parseQuery();
         }
         if (select == 'join') {
@@ -273,12 +276,12 @@ export class ECSCompiler extends Tokenizer {
         }
     }
 
-    parseEvent() {
+    parseEventName() {
         return this.expectIdent().str;
     }
 
     parseEventList() {
-        return this.parseList(this.parseEvent, ",");
+        return this.parseList(this.parseEventName, ",");
     }
 
     parseCode(): string {
@@ -286,12 +289,16 @@ export class ECSCompiler extends Tokenizer {
         let tok = this.expectTokenTypes([ECSTokenType.CodeFragment]);
         let code = tok.str.substring(3, tok.str.length-3);
         let lines = code.split('\n');
-        let re = /^\s*(;|\/\/|$)/; // ignore comments and blank lines
+        if (this.debuginfo) this.addDebugInfo(lines, tok.$loc.line);
+        return lines.join('\n');
+    }
+
+    addDebugInfo(lines: string[], startline: number) {
+        const re = /^\s*(;|\/\/|$)/; // ignore comments and blank lines
         for (let i=0; i<lines.length; i++) {
             if (!lines[i].match(re))
-                lines[i] = this.em.dialect.debug_line(this.path, tok.$loc.line+i) + '\n' + lines[i];
+                lines[i] = this.em.dialect.debug_line(this.path, startline+i) + '\n' + lines[i];
         }
-        return lines.join('\n');
     }
     
     parseScope() : EntityScope {
diff --git a/src/common/ecs/ecs.ts b/src/common/ecs/ecs.ts
index e1c99434..d7604f48 100644
--- a/src/common/ecs/ecs.ts
+++ b/src/common/ecs/ecs.ts
@@ -115,7 +115,9 @@ export interface System extends SourceLocated {
     tempbytes?: number;
 }
 
-export type SelectType = 'once' | 'foreach' | 'join' | 'with' | 'if' | 'select';
+export const SELECT_TYPE = ['once', 'foreach', 'join', 'with', 'if', 'select'] as const;
+
+export type SelectType = typeof SELECT_TYPE[number];
 
 export interface ActionBase extends SourceLocated {
     select: SelectType;
@@ -1062,9 +1064,9 @@ export class EntityScope implements SourceLocated {
                     let codeeval = new ActionEval(this, sys, action);
                     codeeval.tmplabel = tmplabel;
                     codeeval.begin();
-                    s += this.dialect.comment(`<action ${sys.name}:${event}>`); // TODO
+                    s += this.dialect.comment(`start action ${sys.name} ${event}`); // TODO
                     s += codeeval.codeToString();
-                    s += this.dialect.comment(`</action ${sys.name}:${event}>`);
+                    s += this.dialect.comment(`end action ${sys.name} ${event}`);
                     // TODO: check that this happens once?
                     codeeval.end();
                     numActions++;
diff --git a/src/common/tokenizer.ts b/src/common/tokenizer.ts
index 1dd1c5ba..1b7c3fc9 100644
--- a/src/common/tokenizer.ts
+++ b/src/common/tokenizer.ts
@@ -171,7 +171,7 @@ export class Tokenizer {
         }
         return tok;
     }
-    expectTokens(strlist: string[], msg?: string): Token {
+    expectTokens(strlist: readonly string[], msg?: string): Token {
         let tok = this.consumeToken();
         let tokstr = tok.str;
         if (!strlist.includes(tokstr)) {
diff --git a/src/test/testecs.ts b/src/test/testecs.ts
index 59d98f5e..2498062d 100644
--- a/src/test/testecs.ts
+++ b/src/test/testecs.ts
@@ -1,4 +1,6 @@
-import { readdirSync, readFileSync } from "fs";
+import assert from "assert";
+import { execFileSync } from "child_process";
+import { readdirSync, readFileSync, writeFileSync } from "fs";
 import { describe } from "mocha";
 import { ECSCompiler } from "../common/ecs/compiler";
 import { Dialect_CA65, EntityManager, SourceFileExport } from "../common/ecs/ecs";
@@ -338,7 +340,7 @@ scope Root
 end
 
 `, 'foo.txt');
-        console.log('json', c.em.toJSON());
+        //console.log('json', c.em.toJSON());
         let src = new SourceFileExport();
         c.exportToFile(src);
         // TODO: test?
@@ -368,14 +370,27 @@ describe('Tokenizer', function() {
 describe('Compiler', function() {
     let testdir = './test/ecs/';
     let files = readdirSync(testdir).filter(f => f.endsWith('.ecs'));
-    files.forEach((ecspath) => {
+    files.forEach((ecsfn) => {
+        let goodfn = ecsfn.replace('.ecs','.txt')
+        let srcpath = testdir + ecsfn;
+        let destpath = testdir + goodfn;
         let dialect = new Dialect_CA65();
         let em = new EntityManager(dialect);
+        em.mainPath = srcpath;
         let compiler = new ECSCompiler(em);
-        let code = readFileSync(testdir + ecspath, 'utf-8');
-        compiler.parseFile(code, ecspath);
+        compiler.getImportFile = (path: string) => {
+            return readFileSync(testdir + path, 'utf-8');
+        }
+        let code = readFileSync(srcpath, 'utf-8');
+        compiler.parseFile(code, srcpath);
         let out = new SourceFileExport();
         em.exportToFile(out);
-        console.log(out.toString());
+        let outtxt = out.toString();
+        let goodtxt = readFileSync(destpath, 'utf-8');
+        if (outtxt.trim() != goodtxt.trim()) {
+            writeFileSync('/tmp/' + goodfn, outtxt, 'utf-8');
+            execFileSync('/usr/bin/diff', [srcpath, destpath]);
+            throw new Error(ecsfn + ' did not match test file');
+        }
     });
 });
diff --git a/src/worker/tools/ecs.ts b/src/worker/tools/ecs.ts
index 4d2de328..f537cc05 100644
--- a/src/worker/tools/ecs.ts
+++ b/src/worker/tools/ecs.ts
@@ -16,6 +16,7 @@ export function assembleECS(step: BuildStep): BuildStepResult {
     if (staleFiles(step, [destpath])) {
         let code = getWorkFileAsString(step.path);
         try {
+            compiler.debuginfo = true;
             compiler.parseFile(code, step.path);
             let outtext = compiler.export().toString();
             putWorkFile(destpath, outtext);
diff --git a/test/ecs/basic1.txt b/test/ecs/basic1.txt
new file mode 100644
index 00000000..e69de29b
diff --git a/test/ecs/vcs1.ecs b/test/ecs/vcs1.ecs
new file mode 100644
index 00000000..0044cad0
--- /dev/null
+++ b/test/ecs/vcs1.ecs
@@ -0,0 +1,235 @@
+
+//#resource "vcs-ca65.h"
+
+system Init
+  on main_init do once
+---
+.include "vcs-ca65.h"
+.define PAL 0
+__NMI:
+__Reset:
+__BRK:
+    CLEAN_START
+{{bss_init}}	; initialize data segment
+{{!start}}	; start main routine
+.segment "VECTORS"
+Return:    .word $6060
+VecNMI:
+VecReset:  .word Main::__Reset
+VecBRK:    .word Main::__BRK
+---
+end
+
+component Player
+end
+
+component KernelSection
+  lines: 1..255
+end
+
+component BGColor
+  bgcolor: 0..255
+end
+
+component PFColor
+  pfcolor: 0..255
+end
+
+component Playfield
+   pf: 0..0xffffff
+end
+
+component AsymPlayfield
+   pfleft: 0..0xffffff
+   pfright: 0..0xffffff
+end
+
+component VersatilePlayfield
+  data: array of 0..255 baseoffset -1
+end
+
+system FrameLoop
+  on start do once 
+---
+@NextFrame:
+    FRAME_START
+    {{emit preframe}}
+    KERNEL_START
+    {{emit kernel}}
+    KERNEL_END
+    {{emit postframe}}
+    FRAME_END
+    {{emit nextframe}}
+    jmp @NextFrame    ; loop to next frame
+---
+end
+
+system ResetSwitch
+    on nextframe do once
+---
+    lsr SWCHB	      ; test Game Reset switch
+    bcs @NoStart
+    {{!resetswitch}}
+@NoStart:
+---
+end
+
+system ResetConsole
+    on resetswitch do once
+---
+    jmp Main::__Reset ; jump to Reset handler
+---
+end
+
+system JoyButton
+    on postframe do foreach [Player]
+---
+    lda {{index INPT4}}	;read button input
+    bmi @NotPressed
+    {{emit joybutton}}
+@NotPressed:
+---
+end
+
+system Joystick
+    locals 1
+    on postframe do once
+---
+; 2 control inputs share a single byte, 4 bits each
+    lda SWCHA
+    sta {{$0}}
+---
+    on postframe do foreach [Player]
+---
+    asl {{$0}}
+    bcs @SkipMoveRight
+    {{!joyright}}
+@SkipMoveRight:
+    asl {{$0}}
+    bcs @SkipMoveLeft
+    {{!joyleft}}
+@SkipMoveLeft:
+    asl {{$0}}
+    bcs @SkipMoveDown
+    {{!joydown}}
+@SkipMoveDown:
+    asl {{$0}}
+    bcs @SkipMoveUp
+    {{!joyup}}
+@SkipMoveUp:
+---
+end
+
+system SetHorizPos
+    on SetHorizPos do once
+---
+; SetHorizPos routine
+; A = X coordinate
+; Y = player number (0 or 1)
+    sta WSYNC	; start a new line
+    sec		    ; set carry flag
+    nop
+@DivideLoop:
+    sbc #15		; subtract 15
+    bcs @DivideLoop	; branch until negative
+    eor #7		; calculate fine offset
+    asl
+    asl
+    asl
+    asl
+    sta RESP0,y	; fix coarse position
+    sta HMP0,y	; set fine offset
+---
+end
+
+
+system StaticKernel
+  on preframe do foreach [KernelSection] limit 1
+---
+    {{!kernelsetup}}
+---
+  on kernel do foreach [KernelSection]
+---
+    sta WSYNC
+    {{!kernelsetup}}
+    ldy {{<lines}}
+@loop:
+    sta WSYNC
+    {{!scanline}}
+    dey
+    bne @loop
+    {{!kerneldone}}
+---
+  on kernelsetup do if [BGColor]
+---
+    lda {{<bgcolor}}
+    sta COLUBK
+---
+  on kernelsetup do if [PFColor]
+---
+    lda {{get pfcolor}}
+    sta COLUPF
+---
+  on kernelsetup do if [Playfield]
+---
+    lda {{get pf 0}}
+    sta PF0
+    lda {{get pf 8}}
+    sta PF1
+    lda {{get pf 16}}
+    sta PF2
+---
+end
+
+///
+
+demo Main
+  using FrameLoop, ResetSwitch, ResetConsole
+  using StaticKernel, JoyButton
+  entity [Player]
+  end
+  entity [KernelSection,BGColor]
+    const lines = 2
+    const bgcolor = $18
+  end
+  entity [KernelSection,BGColor]
+    const lines = 2
+    const bgcolor = $16
+  end
+  entity [KernelSection,BGColor]
+    const lines = 2
+    const bgcolor = $14
+  end
+  entity [KernelSection,BGColor]
+    const lines = 2
+    const bgcolor = $12
+  end
+  entity  [KernelSection,BGColor,Playfield]
+    const lines = 10
+    const bgcolor = $14
+    const pf = 0x125244
+  end
+  entity Trees [KernelSection,BGColor,PFColor,Playfield]
+    const lines = 50
+    const bgcolor = $14
+    const pf = 0x112244
+  end
+  entity  [KernelSection,BGColor,PFColor,Playfield]
+    const lines = 50
+    const bgcolor = $16
+    const pf = 0x124
+  end
+  entity [KernelSection,BGColor,Playfield]
+    const lines = 10
+    const bgcolor = $18
+    const pf = 0
+  end
+  
+  system Local
+    locals 1
+    on joybutton do foreach [PFColor] limit 1 ---
+    inc {{$0}}
+    inc {{set Trees.pfcolor}}
+    ---
+  end
+end
diff --git a/test/ecs/vcs1.txt b/test/ecs/vcs1.txt
new file mode 100644
index 00000000..d4008144
--- /dev/null
+++ b/test/ecs/vcs1.txt
@@ -0,0 +1,241 @@
+.scope Main
+.zeropage
+PFColor_pfcolor_b0:
+.res 1
+.res 1
+Local_tmp:
+.res 1
+.code
+KernelSection_lines_b0:
+.byte 2
+.byte 2
+.byte 2
+.byte 2
+.byte 10
+.byte 50
+.byte 50
+.byte 10
+BGColor_bgcolor_b0:
+.byte 24
+.byte 22
+.byte 20
+.byte 18
+.byte 20
+.byte 20
+.byte 22
+.byte 24
+Playfield_pf_b0:
+.byte 68
+.byte 68
+.byte 36
+.byte 0
+Playfield_pf_b8:
+.byte 82
+.byte 34
+.byte 1
+.byte 0
+Playfield_pf_b16:
+.byte 18
+.byte 17
+.byte 0
+.byte 0
+Main__INITDATA:
+.byte 0
+.byte 0
+__Start:
+.code
+
+;;; start action Init main_init
+
+.include "vcs-ca65.h"
+.define PAL 0
+__NMI:
+__Reset:
+__BRK:
+    CLEAN_START
+
+    ldy #2
+:   lda Main__INITDATA-1,y
+    sta PFColor_pfcolor_b0-1,y
+    dey
+    bne :-
+	; initialize data segment
+.code
+
+;;; start action FrameLoop start
+
+FrameLoop__start__2__NextFrame:
+    FRAME_START
+    .code
+
+;;; start action StaticKernel preframe
+
+    .code
+
+;;; start action StaticKernel kernelsetup
+
+    lda #24
+    sta COLUBK
+
+;;; end action StaticKernel kernelsetup
+
+;;; start action StaticKernel kernelsetup
+
+    cpx #0+2
+    bcs StaticKernel__kernelsetup__5____skipxhi
+    
+    cpx #0
+    bcc StaticKernel__kernelsetup__5____skipxlo
+    
+    lda PFColor_pfcolor_b0,x
+    sta COLUPF
+
+StaticKernel__kernelsetup__5____skipxlo:
+
+StaticKernel__kernelsetup__5____skipxhi:
+
+;;; end action StaticKernel kernelsetup
+
+;;; start action StaticKernel kernelsetup
+
+    cpx #0+4
+    bcs StaticKernel__kernelsetup__6____skipxhi
+    
+    cpx #0
+    bcc StaticKernel__kernelsetup__6____skipxlo
+    
+    lda Playfield_pf_b0,x
+    sta PF0
+    lda Playfield_pf_b8,x
+    sta PF1
+    lda Playfield_pf_b16,x
+    sta PF2
+
+StaticKernel__kernelsetup__6____skipxlo:
+
+StaticKernel__kernelsetup__6____skipxhi:
+
+;;; end action StaticKernel kernelsetup
+
+
+;;; end action StaticKernel preframe
+
+    KERNEL_START
+    .code
+
+;;; start action StaticKernel kernel
+
+    ldx #0
+StaticKernel__kernel__7____each:
+    
+    sta WSYNC
+    .code
+
+;;; start action StaticKernel kernelsetup
+
+    lda BGColor_bgcolor_b0,x
+    sta COLUBK
+
+;;; end action StaticKernel kernelsetup
+
+;;; start action StaticKernel kernelsetup
+
+    cpx #5+2
+    bcs StaticKernel__kernelsetup__9____skipxhi
+    
+    cpx #5
+    bcc StaticKernel__kernelsetup__9____skipxlo
+    
+    lda PFColor_pfcolor_b0-5,x
+    sta COLUPF
+
+StaticKernel__kernelsetup__9____skipxlo:
+
+StaticKernel__kernelsetup__9____skipxhi:
+
+;;; end action StaticKernel kernelsetup
+
+;;; start action StaticKernel kernelsetup
+
+    cpx #4
+    bcc StaticKernel__kernelsetup__10____skipxlo
+    
+    lda Playfield_pf_b0-4,x
+    sta PF0
+    lda Playfield_pf_b8-4,x
+    sta PF1
+    lda Playfield_pf_b16-4,x
+    sta PF2
+
+StaticKernel__kernelsetup__10____skipxlo:
+
+;;; end action StaticKernel kernelsetup
+
+    ldy KernelSection_lines_b0,x
+StaticKernel__kernel__7__loop:
+    sta WSYNC
+    
+    dey
+    bne StaticKernel__kernel__7__loop
+    
+
+    inx
+    cpx #8
+    bne StaticKernel__kernel__7____each
+StaticKernel__kernel__7____exit:
+
+;;; end action StaticKernel kernel
+
+    KERNEL_END
+    .code
+
+;;; start action JoyButton postframe
+
+    lda INPT4	;read button input
+    bmi JoyButton__postframe__11__NotPressed
+    .code
+
+;;; start action Local joybutton
+
+    inc Local_tmp+0
+    inc PFColor_pfcolor_b0
+    
+;;; end action Local joybutton
+
+JoyButton__postframe__11__NotPressed:
+
+;;; end action JoyButton postframe
+
+    FRAME_END
+    .code
+
+;;; start action ResetSwitch nextframe
+
+    lsr SWCHB	      ; test Game Reset switch
+    bcs ResetSwitch__nextframe__13__NoStart
+    .code
+
+;;; start action ResetConsole resetswitch
+
+    jmp Main::__Reset ; jump to Reset handler
+
+;;; end action ResetConsole resetswitch
+
+ResetSwitch__nextframe__13__NoStart:
+
+;;; end action ResetSwitch nextframe
+
+    jmp FrameLoop__start__2__NextFrame    ; loop to next frame
+
+;;; end action FrameLoop start
+	; start main routine
+.segment "VECTORS"
+Return:    .word $6060
+VecNMI:
+VecReset:  .word Main::__Reset
+VecBRK:    .word Main::__BRK
+
+;;; end action Init main_init
+
+.endscope
+Main__Start = Main::__Start
\ No newline at end of file