diff --git a/etc/aiscript.api.md b/etc/aiscript.api.md
index c20a03e2..6ca83a88 100644
--- a/etc/aiscript.api.md
+++ b/etc/aiscript.api.md
@@ -353,12 +353,14 @@ type FnTypeSource = NodeBase & {
 type For = NodeBase & {
     type: 'for';
     label?: string;
-    var?: string;
-    from?: Expression;
-    to?: Expression;
-    times?: Expression;
     for: Statement | Expression;
-};
+} & ({
+    var: string;
+    from: Expression;
+    to: Expression;
+} | {
+    times: Expression;
+});
 
 // @public (undocumented)
 function getLangVersion(input: string): string | null;
@@ -669,7 +671,7 @@ type Return = NodeBase & {
 
 // @public (undocumented)
 export class Scope {
-    constructor(layerdStates?: Scope['layerdStates'], parent?: Scope, name?: Scope['name'], nsName?: string);
+    constructor(layeredStates?: Scope['layeredStates'], parent?: Scope, name?: Scope['name'], nsName?: string);
     add(name: string, variable: Variable): void;
     assign(name: string, val: Value): void;
     // (undocumented)
diff --git a/src/error.ts b/src/error.ts
index 2e1acf8e..5ab0b015 100644
--- a/src/error.ts
+++ b/src/error.ts
@@ -1,4 +1,3 @@
-import { TokenKind } from './parser/token.js';
 import type { Pos } from './node.js';
 
 export abstract class AiScriptError extends Error {
@@ -25,9 +24,12 @@ export abstract class AiScriptError extends Error {
 export class NonAiScriptError extends AiScriptError {
 	public name = 'Internal';
 	constructor(error: unknown) {
-		const message = String(
-			(error as { message?: unknown } | null | undefined)?.message ?? error,
-		);
+		let message: string;
+		if (error != null && typeof error === 'object' && 'message' in error) {
+			message = String(error.message);
+		} else {
+			message = String(error);
+		}
 		super(message, error);
 	}
 }
diff --git a/src/interpreter/index.ts b/src/interpreter/index.ts
index 8cdab2ae..a4df6679 100644
--- a/src/interpreter/index.ts
+++ b/src/interpreter/index.ts
@@ -14,7 +14,7 @@ import { getPrimProp } from './primitive-props.js';
 import { Variable } from './variable.js';
 import { Reference } from './reference.js';
 import type { JsValue } from './util.js';
-import type { Value, VFn, VUserFn } from './value.js';
+import type { Value, VFn, VFnParam } from './value.js';
 
 export type LogObject = {
 	scope?: string;
@@ -61,7 +61,7 @@ export class Interpreter {
 				const q = args[0];
 				assertString(q);
 				if (this.opts.in == null) return NULL;
-				const a = await this.opts.in!(q.value);
+				const a = await this.opts.in(q.value);
 				return STR(a);
 			}),
 		};
@@ -280,15 +280,19 @@ export class Interpreter {
 			// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
 			return result ?? NULL;
 		} else {
-			const fnScope = fn.scope!.createChildScope();
+			const fnScope = fn.scope.createChildScope();
 			for (const [i, param] of fn.params.entries()) {
-				const arg = args[i];
-				if (!param.default) expectAny(arg);
-				this.define(fnScope, param.dest, arg ?? param.default!, true);
+				let arg = args[i];
+				if (!param.default) {
+					expectAny(arg);
+				} else if (!arg) {
+					arg = param.default;
+				}
+				this.define(fnScope, param.dest, arg, true);
 			}
 
 			const info: CallInfo = { name: fn.name ?? '<anonymous>', pos };
-			return unWrapRet(await this._run(fn.statements!, fnScope, [...callStack, info]));
+			return unWrapRet(await this._run(fn.statements, fnScope, [...callStack, info]));
 		}
 	}
 
@@ -430,7 +434,7 @@ export class Interpreter {
 			}
 
 			case 'for': {
-				if (node.times) {
+				if ('times' in node) {
 					const times = await this._eval(node.times, scope, callStack);
 					if (isControl(times)) {
 						return times;
@@ -452,11 +456,11 @@ export class Interpreter {
 						}
 					}
 				} else {
-					const from = await this._eval(node.from!, scope, callStack);
+					const from = await this._eval(node.from, scope, callStack);
 					if (isControl(from)) {
 						return from;
 					}
-					const to = await this._eval(node.to!, scope, callStack);
+					const to = await this._eval(node.to, scope, callStack);
 					if (isControl(to)) {
 						return to;
 					}
@@ -464,7 +468,7 @@ export class Interpreter {
 					assertNumber(to);
 					for (let i = from.value; i < from.value + to.value; i++) {
 						const v = await this._eval(node.for, scope.createChildScope(new Map([
-							[node.var!, {
+							[node.var, {
 								isMutable: false,
 								value: NUM(i),
 							}],
@@ -632,8 +636,9 @@ export class Interpreter {
 					return target;
 				}
 				if (isObject(target)) {
-					if (target.value.has(node.name)) {
-						return target.value.get(node.name)!;
+					const value = target.value.get(node.name);
+					if (value != null) {
+						return value;
 					} else {
 						return NULL;
 					}
@@ -660,8 +665,9 @@ export class Interpreter {
 					return item;
 				} else if (isObject(target)) {
 					assertString(i);
-					if (target.value.has(i.value)) {
-						return target.value.get(i.value)!;
+					const value = target.value.get(i.value);
+					if (value != null) {
+						return value;
 					} else {
 						return NULL;
 					}
@@ -698,28 +704,21 @@ export class Interpreter {
 			}
 
 			case 'fn': {
-				const params = await Promise.all(node.params.map(async (param) => {
-					return {
+				const params: VFnParam[] = [];
+				for (const param of node.params) {
+					const defaultValue = param.default ? await this._eval(param.default, scope, callStack) :
+						param.optional ? NULL :
+						undefined;
+					if (defaultValue != null && isControl(defaultValue)) {
+						return defaultValue;
+					}
+					params.push({
 						dest: param.dest,
-						default:
-							param.default ? await this._eval(param.default, scope, callStack) :
-							param.optional ? NULL :
-							undefined,
+						default: defaultValue,
 						// type: (TODO)
-					};
-				}));
-				const control = params
-					.map((param) => param.default)
-					.filter((value) => value != null)
-					.find(isControl);
-				if (control != null) {
-					return control;
+					});
 				}
-				return FN(
-					params as VUserFn['params'],
-					node.children,
-					scope,
-				);
+				return FN(params, node.children, scope);
 			}
 
 			case 'block': {
@@ -887,9 +886,7 @@ export class Interpreter {
 
 		let v: Value | Control = NULL;
 
-		for (let i = 0; i < program.length; i++) {
-			const node = program[i]!;
-
+		for (const node of program) {
 			v = await this._eval(node, scope, callStack);
 			if (v.type === 'return') {
 				this.log('block:return', { scope: scope.name, val: v.value });
diff --git a/src/interpreter/primitive-props.ts b/src/interpreter/primitive-props.ts
index df3c18cc..6bb61b9e 100644
--- a/src/interpreter/primitive-props.ts
+++ b/src/interpreter/primitive-props.ts
@@ -9,9 +9,11 @@ import type { Value, VArr, VFn, VNum, VStr, VError } from './value.js';
 type VWithPP = VNum|VStr|VArr|VError;
 
 const PRIMITIVE_PROPS: {
-	[key in VWithPP['type']]: { [key: string]: (target: Value) => Value }
+	[key in VWithPP['type']]: Map<string, (target: Value) => Value>;
+} & {
+	[key in (Exclude<Value, VWithPP>)['type']]?: never;
 } = {
-	num: {
+	num: new Map(Object.entries({
 		to_str: (target: VNum): VFn => FN_NATIVE(async (_, _opts) => {
 			return STR(target.value.toString());
 		}),
@@ -19,9 +21,9 @@ const PRIMITIVE_PROPS: {
 		to_hex: (target: VNum): VFn => FN_NATIVE(async (_, _opts) => {
 			return STR(target.value.toString(16));
 		}),
-	},
+	})),
 
-	str: {
+	str: new Map(Object.entries({
 		to_num: (target: VStr): VFn => FN_NATIVE(async (_, _opts) => {
 			const parsed = parseInt(target.value, 10);
 			if (isNaN(parsed)) return NULL;
@@ -168,9 +170,9 @@ const PRIMITIVE_PROPS: {
 
 			return STR(target.value.padEnd(width.value, s));
 		}),
-	},
+	})),
 
-	arr: {
+	arr: new Map(Object.entries({
 		len: (target: VArr): VNum => NUM(target.value.length),
 
 		push: (target: VArr): VFn => FN_NATIVE(async ([val], _opts) => {
@@ -219,9 +221,8 @@ const PRIMITIVE_PROPS: {
 
 		filter: (target: VArr): VFn => FN_NATIVE(async ([fn], opts) => {
 			assertFunction(fn);
-			const vals = [] as Value[];
-			for (let i = 0; i < target.value.length; i++) {
-				const item = target.value[i]!;
+			const vals: Value[] = [];
+			for (const [i, item] of target.value.entries()) {
 				const res = await opts.call(fn, [item, NUM(i)]);
 				assertBoolean(res);
 				if (res.value) vals.push(item);
@@ -243,8 +244,7 @@ const PRIMITIVE_PROPS: {
 
 		find: (target: VArr): VFn => FN_NATIVE(async ([fn], opts) => {
 			assertFunction(fn);
-			for (let i = 0; i < target.value.length; i++) {
-				const item = target.value[i]!;
+			for (const [i, item] of target.value.entries()) {
 				const res = await opts.call(fn, [item, NUM(i)]);
 				assertBoolean(res);
 				if (res.value) return item;
@@ -382,8 +382,7 @@ const PRIMITIVE_PROPS: {
 
 		every: (target: VArr): VFn => FN_NATIVE(async ([fn], opts) => {
 			assertFunction(fn);
-			for (let i = 0; i < target.value.length; i++) {
-				const item = target.value[i]!;
+			for (const [i, item] of target.value.entries()) {
 				const res = await opts.call(fn, [item, NUM(i)]);
 				assertBoolean(res);
 				if (!res.value) return FALSE;
@@ -393,8 +392,7 @@ const PRIMITIVE_PROPS: {
 
 		some: (target: VArr): VFn => FN_NATIVE(async ([fn], opts) => {
 			assertFunction(fn);
-			for (let i = 0; i < target.value.length; i++) {
-				const item = target.value[i]!;
+			for (const [i, item] of target.value.entries()) {
 				const res = await opts.call(fn, [item, NUM(i)]);
 				assertBoolean(res);
 				if (res.value) return TRUE;
@@ -423,20 +421,21 @@ const PRIMITIVE_PROPS: {
 			assertNumber(index);
 			return target.value.at(index.value) ?? otherwise ?? NULL;
 		}),
-	},
+	})),
 
-	error: {
+	error: new Map(Object.entries({
 		name: (target: VError): VStr => STR(target.value), 
 
 		info: (target: VError): Value => target.info ?? NULL,
-	},
+	})),
 } as const;
 
 export function getPrimProp(target: Value, name: string): Value {
-	if (Object.hasOwn(PRIMITIVE_PROPS, target.type)) {
-		const props = PRIMITIVE_PROPS[target.type as VWithPP['type']];
-		if (Object.hasOwn(props, name)) {
-			return props[name]!(target);
+	const props = PRIMITIVE_PROPS[target.type];
+	if (props != null) {
+		const prop = props.get(name);
+		if (prop != null) {
+			return prop(target);
 		} else {
 			throw new AiScriptRuntimeError(`No such prop (${name}) in ${target.type}.`);
 		}
diff --git a/src/interpreter/scope.ts b/src/interpreter/scope.ts
index 34142551..c6640c49 100644
--- a/src/interpreter/scope.ts
+++ b/src/interpreter/scope.ts
@@ -4,9 +4,11 @@ import type { Value } from './value.js';
 import type { Variable } from './variable.js';
 import type { LogObject } from './index.js';
 
+export type LayeredStates = [Map<string, Variable>, ...Map<string, Variable>[]]
+
 export class Scope {
 	private parent?: Scope;
-	private layerdStates: Map<string, Variable>[];
+	private layeredStates: LayeredStates;
 	public name: string;
 	public opts: {
 		log?(type: string, params: LogObject): void;
@@ -14,10 +16,10 @@ export class Scope {
 	} = {};
 	public nsName?: string;
 
-	constructor(layerdStates: Scope['layerdStates'] = [], parent?: Scope, name?: Scope['name'], nsName?: string) {
-		this.layerdStates = layerdStates;
+	constructor(layeredStates: Scope['layeredStates'] = [new Map()], parent?: Scope, name?: Scope['name'], nsName?: string) {
+		this.layeredStates = layeredStates;
 		this.parent = parent;
-		this.name = name || (layerdStates.length === 1 ? '<root>' : '<anonymous>');
+		this.name = name || (layeredStates.length === 1 ? '<root>' : '<anonymous>');
 		this.nsName = nsName;
 	}
 
@@ -41,13 +43,13 @@ export class Scope {
 
 	@autobind
 	public createChildScope(states: Map<string, Variable> = new Map(), name?: Scope['name']): Scope {
-		const layer = [states, ...this.layerdStates];
+		const layer: LayeredStates = [states, ...this.layeredStates];
 		return new Scope(layer, this, name);
 	}
 
 	@autobind
 	public createChildNamespaceScope(nsName: string, states: Map<string, Variable> = new Map(), name?: Scope['name']): Scope {
-		const layer = [states, ...this.layerdStates];
+		const layer: LayeredStates = [states, ...this.layeredStates];
 		return new Scope(layer, this, name, nsName);
 	}
 
@@ -57,9 +59,10 @@ export class Scope {
 	 */
 	@autobind
 	public get(name: string): Value {
-		for (const layer of this.layerdStates) {
-			if (layer.has(name)) {
-				const state = layer.get(name)!.value;
+		for (const layer of this.layeredStates) {
+			const value = layer.get(name);
+			if (value) {
+				const state = value.value;
 				this.log('read', { var: name, val: state });
 				return state;
 			}
@@ -67,7 +70,7 @@ export class Scope {
 
 		throw new AiScriptRuntimeError(
 			`No such variable '${name}' in scope '${this.name}'`,
-			{ scope: this.layerdStates });
+			{ scope: this.layeredStates });
 	}
 
 	/**
@@ -85,7 +88,7 @@ export class Scope {
 	 */
 	@autobind
 	public exists(name: string): boolean {
-		for (const layer of this.layerdStates) {
+		for (const layer of this.layeredStates) {
 			if (layer.has(name)) {
 				this.log('exists', { var: name });
 				return true;
@@ -101,9 +104,9 @@ export class Scope {
 	 */
 	@autobind
 	public getAll(): Map<string, Variable> {
-		const vars = this.layerdStates.reduce((arr, layer) => {
+		const vars = this.layeredStates.reduce((arr, layer) => {
 			return [...arr, ...layer];
-		}, [] as [string, Variable][]);
+		}, [] satisfies [string, Variable][]);
 		return new Map(vars);
 	}
 
@@ -115,11 +118,11 @@ export class Scope {
 	@autobind
 	public add(name: string, variable: Variable): void {
 		this.log('add', { var: name, val: variable });
-		const states = this.layerdStates[0]!;
+		const states = this.layeredStates[0];
 		if (states.has(name)) {
 			throw new AiScriptRuntimeError(
 				`Variable '${name}' already exists in scope '${this.name}'`,
-				{ scope: this.layerdStates });
+				{ scope: this.layeredStates });
 		}
 		states.set(name, variable);
 		if (this.parent == null) this.onUpdated(name, variable.value);
@@ -134,9 +137,9 @@ export class Scope {
 	@autobind
 	public assign(name: string, val: Value): void {
 		let i = 1;
-		for (const layer of this.layerdStates) {
-			if (layer.has(name)) {
-				const variable = layer.get(name)!;
+		for (const layer of this.layeredStates) {
+			const variable = layer.get(name);
+			if (variable != null) {
 				if (!variable.isMutable) {
 					throw new AiScriptRuntimeError(`Cannot assign to an immutable variable ${name}.`);
 				}
@@ -144,7 +147,7 @@ export class Scope {
 				variable.value = val;
 
 				this.log('assign', { var: name, val: val });
-				if (i === this.layerdStates.length) this.onUpdated(name, val);
+				if (i === this.layeredStates.length) this.onUpdated(name, val);
 				return;
 			}
 			i++;
@@ -152,6 +155,6 @@ export class Scope {
 
 		throw new AiScriptRuntimeError(
 			`No such variable '${name}' in scope '${this.name}'`,
-			{ scope: this.layerdStates });
+			{ scope: this.layeredStates });
 	}
 }
diff --git a/src/node.ts b/src/node.ts
index 1651e849..ae2048d6 100644
--- a/src/node.ts
+++ b/src/node.ts
@@ -82,12 +82,14 @@ export type Each = NodeBase & {
 export type For = NodeBase & {
 	type: 'for'; // for文
 	label?: string; // ラベル
-	var?: string; // イテレータ変数名
-	from?: Expression; // 開始値
-	to?: Expression; // 終値
-	times?: Expression; // 回数
 	for: Statement | Expression; // 本体処理
-};
+} & ({
+	var: string; // イテレータ変数名
+	from: Expression; // 開始値
+	to: Expression; // 終値
+} | {
+	times: Expression; // 回数
+});
 
 export type Loop = NodeBase & {
 	type: 'loop'; // loop文
diff --git a/src/parser/plugins/validate-jump-statements.ts b/src/parser/plugins/validate-jump-statements.ts
index 9828bca9..7b4264ff 100644
--- a/src/parser/plugins/validate-jump-statements.ts
+++ b/src/parser/plugins/validate-jump-statements.ts
@@ -30,7 +30,7 @@ function getCorrespondingBlock(ancestors: Ast.Node[], label?: string): Ast.Each
 	return;
 }
 
-function validateNode(node: Ast.Node, ancestors: Ast.Node[]): Ast.Node {
+function validateNode<T extends Ast.Node>(node: T, ancestors: Ast.Node[]): T {
 	switch (node.type) {
 		case 'return': {
 			if (!ancestors.some(({ type }) => type === 'fn')) {
@@ -55,8 +55,10 @@ function validateNode(node: Ast.Node, ancestors: Ast.Node[]): Ast.Node {
 					break;
 				}
 				case 'for': {
-					if (block.times != null && ancestors.includes(block.times)) {
-						throw new AiScriptSyntaxError('break corresponding to for is not allowed in the count', node.loc.start);
+					if ('times' in block) {
+						if (ancestors.includes(block.times)) {
+							throw new AiScriptSyntaxError('break corresponding to for is not allowed in the count', node.loc.start);
+						}
 					} else if (ancestors.some((ancestor) => ancestor === block.from || ancestor === block.to)) {
 						throw new AiScriptSyntaxError('break corresponding to for is not allowed in the range', node.loc.start);
 					}
@@ -107,8 +109,10 @@ function validateNode(node: Ast.Node, ancestors: Ast.Node[]): Ast.Node {
 						break;
 					}
 					case 'for': {
-						if (block.times != null && ancestors.includes(block.times)) {
-							throw new AiScriptSyntaxError('continue corresponding to for is not allowed in the count', node.loc.start);
+						if ('times' in block) {
+							if (ancestors.includes(block.times)) {
+								throw new AiScriptSyntaxError('continue corresponding to for is not allowed in the count', node.loc.start);
+							}
 						} else if (ancestors.some((ancestor) => ancestor === block.from || ancestor === block.to)) {
 							throw new AiScriptSyntaxError('continue corresponding to for is not allowed in the range', node.loc.start);
 						}
diff --git a/src/parser/plugins/validate-keyword.ts b/src/parser/plugins/validate-keyword.ts
index c134232c..a68ad9e5 100644
--- a/src/parser/plugins/validate-keyword.ts
+++ b/src/parser/plugins/validate-keyword.ts
@@ -87,7 +87,7 @@ function validateTypeParams(node: Ast.Fn | Ast.FnTypeSource): void {
 	}
 }
 
-function validateNode(node: Ast.Node): Ast.Node {
+function validateNode<T extends Ast.Node>(node: T): T {
 	switch (node.type) {
 		case 'def': {
 			validateDest(node.dest);
@@ -119,7 +119,7 @@ function validateNode(node: Ast.Node): Ast.Node {
 			if (node.label != null && reservedWord.includes(node.label)) {
 				throwReservedWordError(node.label, node.loc);
 			}
-			if (node.var != null && reservedWord.includes(node.var)) {
+			if ('var' in node && reservedWord.includes(node.var)) {
 				throwReservedWordError(node.var, node.loc);
 			}
 			break;
diff --git a/src/parser/plugins/validate-type.ts b/src/parser/plugins/validate-type.ts
index 1d043919..ba613c31 100644
--- a/src/parser/plugins/validate-type.ts
+++ b/src/parser/plugins/validate-type.ts
@@ -23,7 +23,7 @@ function collectTypeParams(node: Ast.Node, ancestors: Ast.Node[]): Ast.TypeParam
 	return items;
 }
 
-function validateNode(node: Ast.Node, ancestors: Ast.Node[]): Ast.Node {
+function validateNode<T extends Ast.Node>(node: T, ancestors: Ast.Node[]): T {
 	switch (node.type) {
 		case 'def': {
 			if (node.varType != null) {
diff --git a/src/parser/scanner.ts b/src/parser/scanner.ts
index cb86984f..9050f176 100644
--- a/src/parser/scanner.ts
+++ b/src/parser/scanner.ts
@@ -4,7 +4,7 @@ import { TOKEN, TokenKind } from './token.js';
 import { unexpectedTokenError } from './utils.js';
 
 import type { ITokenStream } from './streams/token-stream.js';
-import type { Token, TokenPosition } from './token.js';
+import type { IdentifierOrLiteralToken, NormalToken, SimpleToken, TemplateExprToken, TemplateToken, TokenPosition } from './token.js';
 
 const spaceChars = [' ', '\t'];
 const lineBreakChars = ['\r', '\n'];
@@ -14,9 +14,9 @@ const wordChar = /^[A-Za-z0-9_]$/;
 /**
  * 入力文字列からトークンを読み取るクラス
 */
-export class Scanner implements ITokenStream {
+export class Scanner implements ITokenStream<NormalToken> {
 	private stream: CharStream;
-	private _tokens: Token[] = [];
+	private _tokens: [NormalToken, ...NormalToken[]];
 
 	constructor(source: string)
 	constructor(stream: CharStream)
@@ -26,14 +26,14 @@ export class Scanner implements ITokenStream {
 		} else {
 			this.stream = x;
 		}
-		this._tokens.push(this.readToken());
+		this._tokens = [this.readToken()];
 	}
 
 	/**
 	 * カーソル位置にあるトークンを取得します。
 	*/
-	public getToken(): Token {
-		return this._tokens[0]!;
+	public getToken(): NormalToken {
+		return this._tokens[0];
 	}
 
 	/**
@@ -46,17 +46,10 @@ export class Scanner implements ITokenStream {
 	/**
 	 * カーソル位置にあるトークンの種類を取得します。
 	*/
-	public getTokenKind(): TokenKind {
+	public getTokenKind(): NormalToken['kind'] {
 		return this.getToken().kind;
 	}
 
-	/**
-	 * カーソル位置にあるトークンに含まれる値を取得します。
-	*/
-	public getTokenValue(): string {
-		return this.getToken().value!;
-	}
-
 	/**
 	 * カーソル位置にあるトークンの位置情報を取得します。
 	*/
@@ -69,7 +62,7 @@ export class Scanner implements ITokenStream {
 	*/
 	public next(): void {
 		// 現在のトークンがEOFだったら次のトークンに進まない
-		if (this._tokens[0]!.kind === TokenKind.EOF) {
+		if (this._tokens[0].kind === TokenKind.EOF) {
 			return;
 		}
 
@@ -83,7 +76,7 @@ export class Scanner implements ITokenStream {
 	/**
 	 * トークンの先読みを行います。カーソル位置は移動されません。
 	*/
-	public lookahead(offset: number): Token {
+	public lookahead(offset: number): NormalToken {
 		while (this._tokens.length <= offset) {
 			this._tokens.push(this.readToken());
 		}
@@ -95,21 +88,21 @@ export class Scanner implements ITokenStream {
 	 * カーソル位置にあるトークンの種類が指定したトークンの種類と一致することを確認します。
 	 * 一致しなかった場合には文法エラーを発生させます。
 	*/
-	public expect(kind: TokenKind): void {
+	public expect(kind: NormalToken['kind']): void {
 		if (!this.is(kind)) {
 			throw unexpectedTokenError(this.getTokenKind(), this.getPos());
 		}
 	}
 
-	private readToken(): Token {
+	private readToken(): NormalToken {
 		let hasLeftSpacing = false;
 
 		while (true) {
-			if (this.stream.eof) {
+			if (this.stream.eof()) {
 				return TOKEN(TokenKind.EOF, this.stream.getPos(), { hasLeftSpacing });
 			}
 			// skip spasing
-			if (spaceChars.includes(this.stream.char)) {
+			if (spaceChars.includes(this.stream.char())) {
 				this.stream.next();
 				hasLeftSpacing = true;
 				continue;
@@ -118,17 +111,17 @@ export class Scanner implements ITokenStream {
 			// トークン位置を記憶
 			const pos = this.stream.getPos();
 
-			if (lineBreakChars.includes(this.stream.char)) {
+			if (lineBreakChars.includes(this.stream.char())) {
 				this.skipEmptyLines();
 				return TOKEN(TokenKind.NewLine, pos, { hasLeftSpacing });
 			}
 
 			// noFallthroughCasesInSwitchと関数の返り値の型を利用し、全ての場合分けがreturnかcontinueで適切に処理されることを強制している
 			// その都合上、break文の使用ないしこのswitch文の後に処理を書くことは極力避けてほしい
-			switch (this.stream.char) {
+			switch (this.stream.char()) {
 				case '!': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '=') {
+					if (!this.stream.eof() && (this.stream.char()) === '=') {
 						this.stream.next();
 						return TOKEN(TokenKind.NotEq, pos, { hasLeftSpacing });
 					} else {
@@ -141,15 +134,15 @@ export class Scanner implements ITokenStream {
 				}
 				case '#': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '#') {
+					if (!this.stream.eof() && (this.stream.char()) === '#') {
 						this.stream.next();
-						if (!this.stream.eof && (this.stream.char as string) === '#') {
+						if (!this.stream.eof() && (this.stream.char()) === '#') {
 							this.stream.next();
 							return TOKEN(TokenKind.Sharp3, pos, { hasLeftSpacing });
 						} else {
 							throw new AiScriptSyntaxError('invalid sequence of characters: "##"', pos);
 						}
-					} else if (!this.stream.eof && (this.stream.char as string) === '[') {
+					} else if (!this.stream.eof() && (this.stream.char()) === '[') {
 						this.stream.next();
 						return TOKEN(TokenKind.OpenSharpBracket, pos, { hasLeftSpacing });
 					} else {
@@ -162,7 +155,7 @@ export class Scanner implements ITokenStream {
 				}
 				case '&': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '&') {
+					if (!this.stream.eof() && (this.stream.char()) === '&') {
 						this.stream.next();
 						return TOKEN(TokenKind.And2, pos, { hasLeftSpacing });
 					} else {
@@ -183,7 +176,7 @@ export class Scanner implements ITokenStream {
 				}
 				case '+': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '=') {
+					if (!this.stream.eof() && (this.stream.char()) === '=') {
 						this.stream.next();
 						return TOKEN(TokenKind.PlusEq, pos, { hasLeftSpacing });
 					} else {
@@ -196,7 +189,7 @@ export class Scanner implements ITokenStream {
 				}
 				case '-': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '=') {
+					if (!this.stream.eof() && (this.stream.char()) === '=') {
 						this.stream.next();
 						return TOKEN(TokenKind.MinusEq, pos, { hasLeftSpacing });
 					} else {
@@ -209,11 +202,11 @@ export class Scanner implements ITokenStream {
 				}
 				case '/': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '*') {
+					if (!this.stream.eof() && (this.stream.char()) === '*') {
 						this.stream.next();
 						this.skipCommentRange();
 						continue;
-					} else if (!this.stream.eof && (this.stream.char as string) === '/') {
+					} else if (!this.stream.eof() && (this.stream.char()) === '/') {
 						this.stream.next();
 						this.skipCommentLine();
 						continue;
@@ -223,7 +216,7 @@ export class Scanner implements ITokenStream {
 				}
 				case ':': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === ':') {
+					if (!this.stream.eof() && (this.stream.char()) === ':') {
 						this.stream.next();
 						return TOKEN(TokenKind.Colon2, pos, { hasLeftSpacing });
 					} else {
@@ -236,10 +229,10 @@ export class Scanner implements ITokenStream {
 				}
 				case '<': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '=') {
+					if (!this.stream.eof() && (this.stream.char()) === '=') {
 						this.stream.next();
 						return TOKEN(TokenKind.LtEq, pos, { hasLeftSpacing });
-					} else if (!this.stream.eof && (this.stream.char as string) === ':') {
+					} else if (!this.stream.eof() && (this.stream.char()) === ':') {
 						this.stream.next();
 						return TOKEN(TokenKind.Out, pos, { hasLeftSpacing });
 					} else {
@@ -248,10 +241,10 @@ export class Scanner implements ITokenStream {
 				}
 				case '=': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '=') {
+					if (!this.stream.eof() && (this.stream.char()) === '=') {
 						this.stream.next();
 						return TOKEN(TokenKind.Eq2, pos, { hasLeftSpacing });
-					} else if (!this.stream.eof && (this.stream.char as string) === '>') {
+					} else if (!this.stream.eof() && (this.stream.char()) === '>') {
 						this.stream.next();
 						return TOKEN(TokenKind.Arrow, pos, { hasLeftSpacing });
 					} else {
@@ -260,7 +253,7 @@ export class Scanner implements ITokenStream {
 				}
 				case '>': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '=') {
+					if (!this.stream.eof() && (this.stream.char()) === '=') {
 						this.stream.next();
 						return TOKEN(TokenKind.GtEq, pos, { hasLeftSpacing });
 					} else {
@@ -300,7 +293,7 @@ export class Scanner implements ITokenStream {
 				}
 				case '|': {
 					this.stream.next();
-					if (!this.stream.eof && (this.stream.char as string) === '|') {
+					if (!this.stream.eof() && (this.stream.char()) === '|') {
 						this.stream.next();
 						return TOKEN(TokenKind.Or2, pos, { hasLeftSpacing });
 					} else {
@@ -318,7 +311,7 @@ export class Scanner implements ITokenStream {
 					const wordToken = this.tryReadWord(hasLeftSpacing);
 					if (wordToken) return wordToken;
 
-					throw new AiScriptSyntaxError(`invalid character: "${this.stream.char}"`, pos);
+					throw new AiScriptSyntaxError(`invalid character: "${this.stream.char()}"`, pos);
 				}
 			}
 			// Use `return` or `continue` before reaching this line.
@@ -329,14 +322,14 @@ export class Scanner implements ITokenStream {
 		// Do not add any more code here. This line should be unreachable.
 	}
 
-	private tryReadWord(hasLeftSpacing: boolean): Token | undefined {
+	private tryReadWord(hasLeftSpacing: boolean): SimpleToken | IdentifierOrLiteralToken | undefined {
 		// read a word
 		let value = '';
 
 		const pos = this.stream.getPos();
 
-		while (!this.stream.eof && wordChar.test(this.stream.char)) {
-			value += this.stream.char;
+		while (!this.stream.eof() && wordChar.test(this.stream.char())) {
+			value += this.stream.char();
 			this.stream.next();
 		}
 		if (value.length === 0) {
@@ -413,23 +406,23 @@ export class Scanner implements ITokenStream {
 		}
 	}
 
-	private tryReadDigits(hasLeftSpacing: boolean): Token | undefined {
+	private tryReadDigits(hasLeftSpacing: boolean): IdentifierOrLiteralToken | undefined {
 		let wholeNumber = '';
 		let fractional = '';
 
 		const pos = this.stream.getPos();
 
-		while (!this.stream.eof && digit.test(this.stream.char)) {
-			wholeNumber += this.stream.char;
+		while (!this.stream.eof() && digit.test(this.stream.char())) {
+			wholeNumber += this.stream.char();
 			this.stream.next();
 		}
 		if (wholeNumber.length === 0) {
 			return;
 		}
-		if (!this.stream.eof && this.stream.char === '.') {
+		if (!this.stream.eof() && this.stream.char() === '.') {
 			this.stream.next();
-			while (!this.stream.eof as boolean && digit.test(this.stream.char as string)) {
-				fractional += this.stream.char;
+			while (!this.stream.eof() && digit.test(this.stream.char())) {
+				fractional += this.stream.char();
 				this.stream.next();
 			}
 			if (fractional.length === 0) {
@@ -445,9 +438,9 @@ export class Scanner implements ITokenStream {
 		return TOKEN(TokenKind.NumberLiteral, pos, { hasLeftSpacing, value });
 	}
 
-	private readStringLiteral(hasLeftSpacing: boolean): Token {
+	private readStringLiteral(hasLeftSpacing: boolean): IdentifierOrLiteralToken {
 		let value = '';
-		const literalMark = this.stream.char;
+		const literalMark = this.stream.char();
 		let state: 'string' | 'escape' | 'finish' = 'string';
 
 		const pos = this.stream.getPos();
@@ -456,28 +449,28 @@ export class Scanner implements ITokenStream {
 		while (state !== 'finish') {
 			switch (state) {
 				case 'string': {
-					if (this.stream.eof) {
+					if (this.stream.eof()) {
 						throw new AiScriptUnexpectedEOFError(pos);
 					}
-					if (this.stream.char === '\\') {
+					if (this.stream.char() === '\\') {
 						this.stream.next();
 						state = 'escape';
 						break;
 					}
-					if (this.stream.char === literalMark) {
+					if (this.stream.char() === literalMark) {
 						this.stream.next();
 						state = 'finish';
 						break;
 					}
-					value += this.stream.char;
+					value += this.stream.char();
 					this.stream.next();
 					break;
 				}
 				case 'escape': {
-					if (this.stream.eof) {
+					if (this.stream.eof()) {
 						throw new AiScriptUnexpectedEOFError(pos);
 					}
-					value += this.stream.char;
+					value += this.stream.char();
 					this.stream.next();
 					state = 'string';
 					break;
@@ -487,10 +480,10 @@ export class Scanner implements ITokenStream {
 		return TOKEN(TokenKind.StringLiteral, pos, { hasLeftSpacing, value });
 	}
 
-	private readTemplate(hasLeftSpacing: boolean): Token {
-		const elements: Token[] = [];
+	private readTemplate(hasLeftSpacing: boolean): TemplateToken {
+		const elements: TemplateToken['children'] = [];
 		let buf = '';
-		let tokenBuf: Token[] = [];
+		let tokenBuf: TemplateExprToken['children'] = [];
 		let state: 'string' | 'escape' | 'expr' | 'finish' = 'string';
 		let exprBracketDepth = 0;
 
@@ -502,17 +495,17 @@ export class Scanner implements ITokenStream {
 			switch (state) {
 				case 'string': {
 					// テンプレートの終了が無いままEOFに達した
-					if (this.stream.eof) {
+					if (this.stream.eof()) {
 						throw new AiScriptUnexpectedEOFError(pos);
 					}
 					// エスケープ
-					if (this.stream.char === '\\') {
+					if (this.stream.char() === '\\') {
 						this.stream.next();
 						state = 'escape';
 						break;
 					}
 					// テンプレートの終了
-					if (this.stream.char === '`') {
+					if (this.stream.char() === '`') {
 						this.stream.next();
 						if (buf.length > 0) {
 							elements.push(TOKEN(TokenKind.TemplateStringElement, elementPos, { hasLeftSpacing, value: buf }));
@@ -521,7 +514,7 @@ export class Scanner implements ITokenStream {
 						break;
 					}
 					// 埋め込み式の開始
-					if (this.stream.char === '{') {
+					if (this.stream.char() === '{') {
 						this.stream.next();
 						if (buf.length > 0) {
 							elements.push(TOKEN(TokenKind.TemplateStringElement, elementPos, { hasLeftSpacing, value: buf }));
@@ -532,17 +525,17 @@ export class Scanner implements ITokenStream {
 						state = 'expr';
 						break;
 					}
-					buf += this.stream.char;
+					buf += this.stream.char();
 					this.stream.next();
 					break;
 				}
 				case 'escape': {
 					// エスケープ対象の文字が無いままEOFに達した
-					if (this.stream.eof) {
+					if (this.stream.eof()) {
 						throw new AiScriptUnexpectedEOFError(pos);
 					}
 					// 普通の文字として取り込み
-					buf += this.stream.char;
+					buf += this.stream.char();
 					this.stream.next();
 					// 通常の文字列に戻る
 					state = 'string';
@@ -550,18 +543,18 @@ export class Scanner implements ITokenStream {
 				}
 				case 'expr': {
 					// 埋め込み式の終端記号が無いままEOFに達した
-					if (this.stream.eof) {
+					if (this.stream.eof()) {
 						throw new AiScriptUnexpectedEOFError(pos);
 					}
 					// skip spasing
-					if (spaceChars.includes(this.stream.char)) {
+					if (spaceChars.includes(this.stream.char())) {
 						this.stream.next();
 						continue;
 					}
-					if (this.stream.char === '{') {
+					if (this.stream.char() === '{') {
 						exprBracketDepth++;
 					}
-					if ((this.stream.char as string) === '}') {
+					if ((this.stream.char()) === '}') {
 						// 埋め込み式の終了
 						if (exprBracketDepth === 0) {
 							elements.push(TOKEN(TokenKind.TemplateExprElement, elementPos, { hasLeftSpacing, children: tokenBuf }));
@@ -587,20 +580,20 @@ export class Scanner implements ITokenStream {
 	}
 
 	private skipEmptyLines(): void {
-		while (!this.stream.eof) {
+		while (!this.stream.eof()) {
 			// skip spacing
-			if (spaceChars.includes(this.stream.char) || lineBreakChars.includes(this.stream.char)) {
+			if (spaceChars.includes(this.stream.char()) || lineBreakChars.includes(this.stream.char())) {
 				this.stream.next();
 				continue;
 			}
 
-			if (this.stream.char === '/') {
+			if (this.stream.char() === '/') {
 				this.stream.next();
-				if (!this.stream.eof && (this.stream.char as string) === '*') {
+				if (!this.stream.eof() && (this.stream.char()) === '*') {
 					this.stream.next();
 					this.skipCommentRange();
 					continue;
-				} else if (!this.stream.eof && (this.stream.char as string) === '/') {
+				} else if (!this.stream.eof() && (this.stream.char()) === '/') {
 					this.stream.next();
 					this.skipCommentLine();
 					continue;
@@ -615,10 +608,10 @@ export class Scanner implements ITokenStream {
 
 	private skipCommentLine(): void {
 		while (true) {
-			if (this.stream.eof) {
+			if (this.stream.eof()) {
 				break;
 			}
-			if (this.stream.char === '\n') {
+			if (this.stream.char() === '\n') {
 				break;
 			}
 			this.stream.next();
@@ -627,15 +620,15 @@ export class Scanner implements ITokenStream {
 
 	private skipCommentRange(): void {
 		while (true) {
-			if (this.stream.eof) {
+			if (this.stream.eof()) {
 				throw new AiScriptUnexpectedEOFError(this.stream.getPos());
 			}
-			if (this.stream.char === '*') {
+			if (this.stream.char() === '*') {
 				this.stream.next();
-				if (this.stream.eof) {
+				if (this.stream.eof()) {
 					throw new AiScriptUnexpectedEOFError(this.stream.getPos());
 				}
-				if ((this.stream.char as string) === '/') {
+				if ((this.stream.char()) === '/') {
 					this.stream.next();
 					break;
 				}
diff --git a/src/parser/streams/char-stream.ts b/src/parser/streams/char-stream.ts
index 58b36793..0bc7f8b3 100644
--- a/src/parser/streams/char-stream.ts
+++ b/src/parser/streams/char-stream.ts
@@ -28,15 +28,15 @@ export class CharStream {
 	/**
 	 * ストリームの終わりに達しているかどうかを取得します。
 	*/
-	public get eof(): boolean {
+	public eof(): boolean {
 		return this.endOfPage && this.isLastPage;
 	}
 
 	/**
 	 * カーソル位置にある文字を取得します。
 	*/
-	public get char(): string {
-		if (this.eof) {
+	public char(): string {
+		if (this.eof()) {
 			throw new Error('end of stream');
 		}
 		return this._char!;
@@ -56,7 +56,7 @@ export class CharStream {
 	 * カーソル位置を次の文字へ進めます。
 	*/
 	public next(): void {
-		if (!this.eof && this._char === '\n') {
+		if (!this.eof() && this._char === '\n') {
 			this.line++;
 			this.column = 0;
 		} else {
@@ -90,7 +90,7 @@ export class CharStream {
 	private moveNext(): void {
 		this.loadChar();
 		while (true) {
-			if (!this.eof && this._char === '\r') {
+			if (!this.eof() && this._char === '\r') {
 				this.incAddr();
 				this.loadChar();
 				continue;
@@ -111,7 +111,7 @@ export class CharStream {
 	private movePrev(): void {
 		this.loadChar();
 		while (true) {
-			if (!this.eof && this._char === '\r') {
+			if (!this.eof() && this._char === '\r') {
 				this.decAddr();
 				this.loadChar();
 				continue;
@@ -130,7 +130,7 @@ export class CharStream {
 	}
 
 	private loadChar(): void {
-		if (this.eof) {
+		if (this.eof()) {
 			this._char = undefined;
 		} else {
 			this._char = this.pages.get(this.pageIndex)![this.address]!;
diff --git a/src/parser/streams/token-stream.ts b/src/parser/streams/token-stream.ts
index e21b66a8..b31190eb 100644
--- a/src/parser/streams/token-stream.ts
+++ b/src/parser/streams/token-stream.ts
@@ -5,26 +5,21 @@ import type { Token, TokenPosition } from '../token.js';
 /**
  * トークンの読み取りに関するインターフェース
 */
-export interface ITokenStream {
+export interface ITokenStream<T extends Token = Token> {
 	/**
 	 * カーソル位置にあるトークンを取得します。
 	*/
-	getToken(): Token;
+	getToken(): T;
 
 	/**
 	 * カーソル位置にあるトークンの種類が指定したトークンの種類と一致するかどうかを示す値を取得します。
 	*/
-	is(kind: TokenKind): boolean;
+	is(kind: T['kind']): boolean;
 
 	/**
 	 * カーソル位置にあるトークンの種類を取得します。
 	*/
-	getTokenKind(): TokenKind;
-
-	/**
-	 * カーソル位置にあるトークンに含まれる値を取得します。
-	*/
-	getTokenValue(): string;
+	getTokenKind(): T['kind'];
 
 	/**
 	 * カーソル位置にあるトークンの位置情報を取得します。
@@ -39,13 +34,13 @@ export interface ITokenStream {
 	/**
 	 * トークンの先読みを行います。カーソル位置は移動されません。
 	*/
-	lookahead(offset: number): Token;
+	lookahead(offset: number): T;
 
 	/**
 	 * カーソル位置にあるトークンの種類が指定したトークンの種類と一致することを確認します。
 	 * 一致しなかった場合には文法エラーを発生させます。
 	*/
-	expect(kind: TokenKind): void;
+	expect(kind: T['kind']): void;
 }
 
 /**
@@ -83,13 +78,6 @@ export class TokenStream implements ITokenStream {
 		return this.getTokenKind() === kind;
 	}
 
-	/**
-	 * カーソル位置にあるトークンに含まれる値を取得します。
-	*/
-	public getTokenValue(): string {
-		return this.getToken().value!;
-	}
-
 	/**
 	 * カーソル位置にあるトークンの種類を取得します。
 	*/
diff --git a/src/parser/syntaxes/common.ts b/src/parser/syntaxes/common.ts
index 049f8553..c69a0c4f 100644
--- a/src/parser/syntaxes/common.ts
+++ b/src/parser/syntaxes/common.ts
@@ -1,4 +1,4 @@
-import { TokenKind } from '../token.js';
+import { expectTokenKind, TokenKind } from '../token.js';
 import { AiScriptSyntaxError, AiScriptUnexpectedEOFError } from '../../error.js';
 import { NODE } from '../utils.js';
 import { parseStatement } from './statements.js';
@@ -15,9 +15,10 @@ import type * as Ast from '../../node.js';
 */
 export function parseDest(s: ITokenStream): Ast.Expression {
 	// 全部parseExprに任せるとparseReferenceが型注釈を巻き込んでパースしてしまうためIdentifierのみ個別に処理。
-	if (s.is(TokenKind.Identifier)) {
-		const nameStartPos = s.getPos();
-		const name = s.getTokenValue();
+	const token = s.getToken();
+	if (token.kind === TokenKind.Identifier) {
+		const nameStartPos = token.pos;
+		const name = token.value;
 		s.next();
 		return NODE('identifier', { name }, nameStartPos, s.getPos());
 	} else {
@@ -148,7 +149,9 @@ export function parseLabel(s: ITokenStream): string {
 		throw new AiScriptSyntaxError('cannot use spaces in a label', s.getPos());
 	}
 	s.expect(TokenKind.Identifier);
-	const label = s.getTokenValue();
+	const token = s.getToken();
+	expectTokenKind(token, TokenKind.Identifier);
+	const label = token.value;
 	s.next();
 
 	return label;
diff --git a/src/parser/syntaxes/expressions.ts b/src/parser/syntaxes/expressions.ts
index e249548b..a1080469 100644
--- a/src/parser/syntaxes/expressions.ts
+++ b/src/parser/syntaxes/expressions.ts
@@ -1,7 +1,7 @@
 import { AiScriptSyntaxError, AiScriptUnexpectedEOFError } from '../../error.js';
 import { NODE, unexpectedTokenError } from '../utils.js';
 import { TokenStream } from '../streams/token-stream.js';
-import { TokenKind } from '../token.js';
+import { expectTokenKind, TokenKind } from '../token.js';
 import { parseBlock, parseLabel, parseOptionalSeparator, parseParams } from './common.js';
 import { parseBlockOrStatement } from './statements.js';
 import { parseType, parseTypeParams } from './types.js';
@@ -103,8 +103,9 @@ function parseInfix(s: ITokenStream, left: Ast.Expression, minBp: number): Ast.E
 	}
 
 	if (op === TokenKind.Dot) {
-		s.expect(TokenKind.Identifier);
-		const name = s.getTokenValue();
+		const token = s.getToken();
+		expectTokenKind(token, TokenKind.Identifier);
+		const name = token.value;
 		s.next();
 
 		return NODE('prop', {
@@ -192,8 +193,9 @@ function parsePostfix(s: ITokenStream, expr: Ast.Expression): Ast.Expression {
 
 function parseAtom(s: ITokenStream, isStatic: boolean): Ast.Expression {
 	const startPos = s.getPos();
+	const token = s.getToken();
 
-	switch (s.getTokenKind()) {
+	switch (token.kind) {
 		case TokenKind.IfKeyword: {
 			if (isStatic) break;
 			return parseIf(s);
@@ -219,12 +221,12 @@ function parseAtom(s: ITokenStream, isStatic: boolean): Ast.Expression {
 
 			if (isStatic) break;
 
-			for (const [i, element] of s.getToken().children!.entries()) {
+			for (const [i, element] of token.children.entries()) {
 				switch (element.kind) {
 					case TokenKind.TemplateStringElement: {
 						// トークンの終了位置を取得するために先読み
-						const nextToken = s.getToken().children![i + 1] ?? s.lookahead(1);
-						values.push(NODE('str', { value: element.value! }, element.pos, nextToken.pos));
+						const nextToken = token.children[i + 1] ?? s.lookahead(1);
+						values.push(NODE('str', { value: element.value }, element.pos, nextToken.pos));
 						break;
 					}
 					case TokenKind.TemplateExprElement: {
@@ -251,13 +253,13 @@ function parseAtom(s: ITokenStream, isStatic: boolean): Ast.Expression {
 			return NODE('tmpl', { tmpl: values }, startPos, s.getPos());
 		}
 		case TokenKind.StringLiteral: {
-			const value = s.getTokenValue();
+			const value = token.value;
 			s.next();
 			return NODE('str', { value }, startPos, s.getPos());
 		}
 		case TokenKind.NumberLiteral: {
 			// TODO: validate number value
-			const value = Number(s.getTokenValue());
+			const value = Number(token.value);
 			s.next();
 			return NODE('num', { value }, startPos, s.getPos());
 		}
@@ -568,8 +570,9 @@ function parseReference(s: ITokenStream): Ast.Identifier {
 				break;
 			}
 		}
-		s.expect(TokenKind.Identifier);
-		segs.push(s.getTokenValue());
+		const token = s.getToken();
+		expectTokenKind(token, TokenKind.Identifier);
+		segs.push(token.value);
 		s.next();
 	}
 	return NODE('identifier', { name: segs.join(':') }, startPos, s.getPos());
@@ -592,11 +595,11 @@ function parseObject(s: ITokenStream, isStatic: boolean): Ast.Obj {
 
 	const map = new Map<string, Ast.Expression>();
 	while (!s.is(TokenKind.CloseBrace)) {
-		const keyTokenKind = s.getTokenKind();
-		if (keyTokenKind !== TokenKind.Identifier && keyTokenKind !== TokenKind.StringLiteral) {
-			throw unexpectedTokenError(keyTokenKind, s.getPos());
+		const token = s.getToken();
+		if (token.kind !== TokenKind.Identifier && token.kind !== TokenKind.StringLiteral) {
+			throw unexpectedTokenError(token.kind, s.getPos());
 		}
-		const k = s.getTokenValue();
+		const k = token.value;
 		s.next();
 
 		s.expect(TokenKind.Colon);
diff --git a/src/parser/syntaxes/statements.ts b/src/parser/syntaxes/statements.ts
index d8918adf..2e6a6284 100644
--- a/src/parser/syntaxes/statements.ts
+++ b/src/parser/syntaxes/statements.ts
@@ -1,6 +1,6 @@
 import { AiScriptSyntaxError } from '../../error.js';
-import { CALL_NODE, NODE, unexpectedTokenError } from '../utils.js';
-import { TokenKind } from '../token.js';
+import { CALL_NODE, LOC, NODE, unexpectedTokenError } from '../utils.js';
+import { expectTokenKind, TokenKind } from '../token.js';
 import { parseBlock, parseDest, parseLabel, parseParams } from './common.js';
 import { parseExpr } from './expressions.js';
 import { parseType, parseTypeParams } from './types.js';
@@ -155,9 +155,10 @@ function parseFnDef(s: ITokenStream): Ast.Definition {
 	s.expect(TokenKind.At);
 	s.next();
 
-	s.expect(TokenKind.Identifier);
+	const token = s.getToken();
+	expectTokenKind(token, TokenKind.Identifier);
 	const nameStartPos = s.getPos();
-	const name = s.getTokenValue();
+	const name = token.value;
 	s.next();
 	const dest = NODE('identifier', { name }, nameStartPos, s.getPos());
 
@@ -307,8 +308,9 @@ function parseFor(s: ITokenStream): Ast.For {
 
 		const identPos = s.getPos();
 
-		s.expect(TokenKind.Identifier);
-		const name = s.getTokenValue();
+		const token = s.getToken();
+		expectTokenKind(token, TokenKind.Identifier);
+		const name = token.value;
 		s.next();
 
 		let _from: Ast.Expression;
@@ -334,12 +336,14 @@ function parseFor(s: ITokenStream): Ast.For {
 
 		const body = parseBlockOrStatement(s);
 
-		return NODE('for', {
+		return {
+			type: 'for',
 			var: name,
 			from: _from,
 			to,
 			for: body,
-		}, startPos, s.getPos());
+			loc: LOC(startPos, s.getPos()),
+		};
 	} else {
 		// times syntax
 
@@ -352,10 +356,12 @@ function parseFor(s: ITokenStream): Ast.For {
 	
 		const body = parseBlockOrStatement(s);
 
-		return NODE('for', {
+		return {
+			type: 'for',
 			times,
 			for: body,
-		}, startPos, s.getPos());
+			loc: LOC(startPos, s.getPos()),
+		};
 	}
 }
 
@@ -412,8 +418,9 @@ function parseAttr(s: ITokenStream): Ast.Attribute {
 	s.expect(TokenKind.OpenSharpBracket);
 	s.next();
 
-	s.expect(TokenKind.Identifier);
-	const name = s.getTokenValue();
+	const token = s.getToken();
+	expectTokenKind(token, TokenKind.Identifier);
+	const name = token.value;
 	s.next();
 
 	let value: Ast.Expression;
diff --git a/src/parser/syntaxes/toplevel.ts b/src/parser/syntaxes/toplevel.ts
index 91a07787..e8060289 100644
--- a/src/parser/syntaxes/toplevel.ts
+++ b/src/parser/syntaxes/toplevel.ts
@@ -1,5 +1,5 @@
 import { NODE } from '../utils.js';
-import { TokenKind } from '../token.js';
+import { expectTokenKind, TokenKind } from '../token.js';
 import { AiScriptSyntaxError, AiScriptUnexpectedEOFError } from '../../error.js';
 import { parseDefStatement, parseStatement } from './statements.js';
 import { parseExpr } from './expressions.js';
@@ -67,8 +67,9 @@ export function parseNamespace(s: ITokenStream): Ast.Namespace {
 	s.expect(TokenKind.Colon2);
 	s.next();
 
-	s.expect(TokenKind.Identifier);
-	const name = s.getTokenValue();
+	const token = s.getToken();
+	expectTokenKind(token, TokenKind.Identifier);
+	const name = token.value;
 	s.next();
 
 	const members: (Ast.Namespace | Ast.Definition)[] = [];
@@ -131,8 +132,9 @@ export function parseMeta(s: ITokenStream): Ast.Meta {
 	s.next();
 
 	let name = null;
-	if (s.is(TokenKind.Identifier)) {
-		name = s.getTokenValue();
+	const token = s.getToken();
+	if (token.kind === TokenKind.Identifier) {
+		name = token.value;
 		s.next();
 	}
 
diff --git a/src/parser/syntaxes/types.ts b/src/parser/syntaxes/types.ts
index a29ced1a..dc0258cb 100644
--- a/src/parser/syntaxes/types.ts
+++ b/src/parser/syntaxes/types.ts
@@ -1,5 +1,5 @@
 import { AiScriptSyntaxError, AiScriptUnexpectedEOFError } from '../../error.js';
-import { TokenKind } from '../token.js';
+import { expectTokenKind, TokenKind } from '../token.js';
 import { NODE } from '../utils.js';
 import { parseOptionalSeparator } from './common.js';
 
@@ -51,8 +51,9 @@ export function parseTypeParams(s: ITokenStream): TypeParam[] {
  * ```
 */
 function parseTypeParam(s: ITokenStream): TypeParam {
-	s.expect(TokenKind.Identifier);
-	const name = s.getTokenValue();
+	const token = s.getToken();
+	expectTokenKind(token, TokenKind.Identifier);
+	const name = token.value;
 	s.next();
 
 	return { name };
@@ -154,8 +155,9 @@ function parseNamedType(s: ITokenStream): Ast.TypeSource {
 	const startPos = s.getPos();
 
 	let name: string;
-	if (s.is(TokenKind.Identifier)) {
-		name = s.getTokenValue();
+	const token = s.getToken();
+	if (token.kind === TokenKind.Identifier) {
+		name = token.value;
 		s.next();
 	} else {
 		s.expect(TokenKind.NullKeyword);
diff --git a/src/parser/token.ts b/src/parser/token.ts
index 35b2d4c7..d5b50a4f 100644
--- a/src/parser/token.ts
+++ b/src/parser/token.ts
@@ -1,3 +1,5 @@
+import { unexpectedTokenError } from './utils.js';
+
 export enum TokenKind {
 	EOF,
 	NewLine,
@@ -115,22 +117,99 @@ export enum TokenKind {
 
 export type TokenPosition = { column: number, line: number };
 
-export class Token {
-	constructor(
-		public kind: TokenKind,
-		public pos: TokenPosition,
-		public hasLeftSpacing = false,
-		/** for number literal, string literal */
-		public value?: string,
-		/** for template syntax */
-		public children?: Token[],
-	) { }
+type TokenBase = {
+	kind: TokenKind;
+	pos: TokenPosition;
+	hasLeftSpacing: boolean;
+};
+
+export type EOFToken = TokenBase & {
+	kind: TokenKind.EOF;
+};
+
+export type SimpleToken = TokenBase & {
+	kind: Exclude<
+		TokenKind,
+		TokenKind.EOF
+		| TokenKind.Identifier
+		| TokenKind.NumberLiteral
+		| TokenKind.StringLiteral
+		| TokenKind.Template
+		| TokenKind.TemplateStringElement
+		| TokenKind.TemplateExprElement
+	>;
+}
+
+/** for number literal, string literal */
+export type IdentifierOrLiteralToken = TokenBase & {
+	kind: TokenKind.Identifier | TokenKind.NumberLiteral | TokenKind.StringLiteral;
+	value: string;
+};
+
+/** for template syntax */
+export type TemplateToken = TokenBase & {
+	kind: TokenKind.Template;
+	children: (EOFToken | TemplateExprToken | TemplateStringToken)[];
+};
+
+export type TemplateStringToken = TokenBase & {
+	kind: TokenKind.TemplateStringElement;
+	value: string;
+};
+
+export type TemplateExprToken = TokenBase & {
+	kind: TokenKind.TemplateExprElement;
+	children: NormalToken[];
+};
+
+export type NormalToken = EOFToken | SimpleToken | IdentifierOrLiteralToken | TemplateToken;
+
+export type Token = NormalToken | TemplateStringToken | TemplateExprToken;
+
+export function TOKEN(
+	kind: EOFToken['kind'],
+	pos: TokenPosition,
+	opts?: Omit<EOFToken, 'kind' | 'pos'>,
+): EOFToken;
+export function TOKEN(
+	kind: SimpleToken['kind'],
+	pos: TokenPosition,
+	opts: Omit<SimpleToken, 'kind' | 'pos'>,
+): SimpleToken;
+export function TOKEN(
+	kind: IdentifierOrLiteralToken['kind'],
+	pos: TokenPosition,
+	opts: Omit<IdentifierOrLiteralToken, 'kind' | 'pos'>,
+): IdentifierOrLiteralToken;
+export function TOKEN(
+	kind: TemplateToken['kind'],
+	pos: TokenPosition,
+	opts: Omit<TemplateToken, 'kind' | 'pos'>,
+): TemplateToken;
+export function TOKEN(
+	kind: TemplateStringToken['kind'],
+	pos: TokenPosition,
+	opts: Omit<TemplateStringToken, 'kind' | 'pos'>,
+): TemplateStringToken;
+export function TOKEN(
+	kind: TemplateExprToken['kind'],
+	pos: TokenPosition,
+	opts: Omit<TemplateExprToken, 'kind' | 'pos'>,
+): TemplateExprToken;
+export function TOKEN(
+	kind: TokenBase['kind'],
+	pos: TokenPosition,
+	opts?: Omit<TokenBase, 'kind' | 'pos'>,
+): TokenBase {
+	if (opts == null) {
+		return { kind, pos, hasLeftSpacing: false };
+	} else {
+		return { kind, pos, ...opts };
+	}
 }
 
-/**
- * - opts.value: for number literal, string literal
- * - opts.children: for template syntax
-*/
-export function TOKEN(kind: TokenKind, pos: TokenPosition, opts?: { hasLeftSpacing?: boolean, value?: Token['value'], children?: Token['children'] }): Token {
-	return new Token(kind, pos, opts?.hasLeftSpacing, opts?.value, opts?.children);
+export function expectTokenKind<T extends TokenKind>(token: Token, kind: T): asserts token is Token & { kind: T } {
+	if (token.kind !== kind) {
+		throw unexpectedTokenError(token.kind, token.pos);
+	}
 }
diff --git a/src/parser/utils.ts b/src/parser/utils.ts
index c3e97d77..753e4fbf 100644
--- a/src/parser/utils.ts
+++ b/src/parser/utils.ts
@@ -9,15 +9,11 @@ export function NODE<T extends Ast.Node['type']>(
 	start: Ast.Pos,
 	end: Ast.Pos,
 ): Extract<Ast.Node, { type: T }> {
-	const node: Record<string, unknown> = { type };
-	for (const key of Object.keys(params)) {
-		type Key = keyof typeof params;
-		if (params[key as Key] !== undefined) {
-			node[key] = params[key as Key];
-		}
-	}
-	node.loc = { start, end };
-	return node as Extract<Ast.Node, { type: T }>;
+	return { type, ...params, loc: { start, end } } as Extract<Ast.Node, { type: T }>;
+}
+
+export function LOC(start: Ast.Pos, end: Ast.Pos): Ast.Loc {
+	return { start, end };
 }
 
 export function CALL_NODE(
diff --git a/src/parser/visit.ts b/src/parser/visit.ts
index a5686997..e4cade6d 100644
--- a/src/parser/visit.ts
+++ b/src/parser/visit.ts
@@ -1,10 +1,10 @@
 import type * as Ast from '../node.js';
 
-export function visitNode(node: Ast.Node, fn: (node: Ast.Node, ancestors: Ast.Node[]) => Ast.Node): Ast.Node {
+export function visitNode<T extends Ast.Node>(node: T, fn: <U extends Ast.Node>(node: U, ancestors: Ast.Node[]) => U): T {
 	return visitNodeInner(node, fn, []);
 }
 
-function visitNodeInner(node: Ast.Node, fn: (node: Ast.Node, ancestors: Ast.Node[]) => Ast.Node, ancestors: Ast.Node[]): Ast.Node {
+function visitNodeInner<T extends Ast.Node>(node: T, fn: <T extends Ast.Node>(node: T, ancestors: Ast.Node[]) => T, ancestors: Ast.Node[]): T {
 	const result = fn(node, ancestors);
 	ancestors.push(node);
 
@@ -12,149 +12,146 @@ function visitNodeInner(node: Ast.Node, fn: (node: Ast.Node, ancestors: Ast.Node
 	switch (result.type) {
 		case 'def': {
 			if (result.varType != null) {
-				result.varType = visitNodeInner(result.varType, fn, ancestors) as Ast.Definition['varType'];
+				result.varType = visitNodeInner(result.varType, fn, ancestors);
 			}
-			result.attr = result.attr.map((attr) => visitNodeInner(attr, fn, ancestors) as Ast.Attribute);
-			result.expr = visitNodeInner(result.expr, fn, ancestors) as Ast.Definition['expr'];
+			result.attr = result.attr.map((attr) => visitNodeInner(attr, fn, ancestors));
+			result.expr = visitNodeInner(result.expr, fn, ancestors);
 			break;
 		}
 		case 'return': {
-			result.expr = visitNodeInner(result.expr, fn, ancestors) as Ast.Return['expr'];
+			result.expr = visitNodeInner(result.expr, fn, ancestors);
 			break;
 		}
 		case 'each': {
-			result.items = visitNodeInner(result.items, fn, ancestors) as Ast.Each['items'];
-			result.for = visitNodeInner(result.for, fn, ancestors) as Ast.Each['for'];
+			result.items = visitNodeInner(result.items, fn, ancestors);
+			result.for = visitNodeInner(result.for, fn, ancestors);
 			break;
 		}
 		case 'for': {
-			if (result.from != null) {
-				result.from = visitNodeInner(result.from, fn, ancestors) as Ast.For['from'];
+			if ('from' in result) {
+				result.from = visitNodeInner(result.from, fn, ancestors);
+				result.to = visitNodeInner(result.to, fn, ancestors);
+			} else {
+				result.times = visitNodeInner(result.times, fn, ancestors);
 			}
-			if (result.to != null) {
-				result.to = visitNodeInner(result.to, fn, ancestors) as Ast.For['to'];
-			}
-			if (result.times != null) {
-				result.times = visitNodeInner(result.times, fn, ancestors) as Ast.For['times'];
-			}
-			result.for = visitNodeInner(result.for, fn, ancestors) as Ast.For['for'];
+			result.for = visitNodeInner(result.for, fn, ancestors);
 			break;
 		}
 		case 'loop': {
 			for (let i = 0; i < result.statements.length; i++) {
-				result.statements[i] = visitNodeInner(result.statements[i]!, fn, ancestors) as Ast.Loop['statements'][number];
+				result.statements[i] = visitNodeInner(result.statements[i]!, fn, ancestors);
 			}
 			break;
 		}
 		case 'addAssign':
 		case 'subAssign':
 		case 'assign': {
-			result.expr = visitNodeInner(result.expr, fn, ancestors) as Ast.Assign['expr'];
-			result.dest = visitNodeInner(result.dest, fn, ancestors) as Ast.Assign['dest'];
+			result.expr = visitNodeInner(result.expr, fn, ancestors);
+			result.dest = visitNodeInner(result.dest, fn, ancestors);
 			break;
 		}
 		case 'plus': {
-			result.expr = visitNodeInner(result.expr, fn, ancestors) as Ast.Plus['expr'];
+			result.expr = visitNodeInner(result.expr, fn, ancestors);
 			break;
 		}
 		case 'minus': {
-			result.expr = visitNodeInner(result.expr, fn, ancestors) as Ast.Minus['expr'];
+			result.expr = visitNodeInner(result.expr, fn, ancestors);
 			break;
 		}
 		case 'not': {
-			result.expr = visitNodeInner(result.expr, fn, ancestors) as Ast.Not['expr'];
+			result.expr = visitNodeInner(result.expr, fn, ancestors);
 			break;
 		}
 		case 'if': {
-			result.cond = visitNodeInner(result.cond, fn, ancestors) as Ast.If['cond'];
-			result.then = visitNodeInner(result.then, fn, ancestors) as Ast.If['then'];
+			result.cond = visitNodeInner(result.cond, fn, ancestors);
+			result.then = visitNodeInner(result.then, fn, ancestors);
 			for (const prop of result.elseif) {
-				prop.cond = visitNodeInner(prop.cond, fn, ancestors) as Ast.If['elseif'][number]['cond'];
-				prop.then = visitNodeInner(prop.then, fn, ancestors) as Ast.If['elseif'][number]['then'];
+				prop.cond = visitNodeInner(prop.cond, fn, ancestors);
+				prop.then = visitNodeInner(prop.then, fn, ancestors);
 			}
 			if (result.else != null) {
-				result.else = visitNodeInner(result.else, fn, ancestors) as Ast.If['else'];
+				result.else = visitNodeInner(result.else, fn, ancestors);
 			}
 			break;
 		}
 		case 'fn': {
 			for (const param of result.params) {
 				if (param.default) {
-					param.default = visitNodeInner(param.default!, fn, ancestors) as Ast.Fn['params'][number]['default'];
+					param.default = visitNodeInner(param.default!, fn, ancestors);
 				}
 				if (param.argType != null) {
-					param.argType = visitNodeInner(param.argType, fn, ancestors) as Ast.Fn['params'][number]['argType'];
+					param.argType = visitNodeInner(param.argType, fn, ancestors);
 				}
 			}
 			if (result.retType != null) {
-				result.retType = visitNodeInner(result.retType, fn, ancestors) as Ast.Fn['retType'];
+				result.retType = visitNodeInner(result.retType, fn, ancestors);
 			}
 			for (let i = 0; i < result.children.length; i++) {
-				result.children[i] = visitNodeInner(result.children[i]!, fn, ancestors) as Ast.Fn['children'][number];
+				result.children[i] = visitNodeInner(result.children[i]!, fn, ancestors);
 			}
 			break;
 		}
 		case 'match': {
-			result.about = visitNodeInner(result.about, fn, ancestors) as Ast.Match['about'];
+			result.about = visitNodeInner(result.about, fn, ancestors);
 			for (const prop of result.qs) {
-				prop.q = visitNodeInner(prop.q, fn, ancestors) as Ast.Match['qs'][number]['q'];
-				prop.a = visitNodeInner(prop.a, fn, ancestors) as Ast.Match['qs'][number]['a'];
+				prop.q = visitNodeInner(prop.q, fn, ancestors);
+				prop.a = visitNodeInner(prop.a, fn, ancestors);
 			}
 			if (result.default != null) {
-				result.default = visitNodeInner(result.default, fn, ancestors) as Ast.Match['default'];
+				result.default = visitNodeInner(result.default, fn, ancestors);
 			}
 			break;
 		}
 		case 'block': {
 			for (let i = 0; i < result.statements.length; i++) {
-				result.statements[i] = visitNodeInner(result.statements[i]!, fn, ancestors) as Ast.Block['statements'][number];
+				result.statements[i] = visitNodeInner(result.statements[i]!, fn, ancestors);
 			}
 			break;
 		}
 		case 'exists': {
-			result.identifier = visitNodeInner(result.identifier, fn, ancestors) as Ast.Exists['identifier'];
+			result.identifier = visitNodeInner(result.identifier, fn, ancestors);
 			break;
 		}
 		case 'tmpl': {
 			for (let i = 0; i < result.tmpl.length; i++) {
 				const item = result.tmpl[i]!;
 				if (typeof item !== 'string') {
-					result.tmpl[i] = visitNodeInner(item, fn, ancestors) as Ast.Tmpl['tmpl'][number];
+					result.tmpl[i] = visitNodeInner(item, fn, ancestors);
 				}
 			}
 			break;
 		}
 		case 'obj': {
 			for (const item of result.value) {
-				result.value.set(item[0], visitNodeInner(item[1], fn, ancestors) as Ast.Expression);
+				result.value.set(item[0], visitNodeInner(item[1], fn, ancestors));
 			}
 			break;
 		}
 		case 'arr': {
 			for (let i = 0; i < result.value.length; i++) {
-				result.value[i] = visitNodeInner(result.value[i]!, fn, ancestors) as Ast.Arr['value'][number];
+				result.value[i] = visitNodeInner(result.value[i]!, fn, ancestors);
 			}
 			break;
 		}
 		case 'call': {
-			result.target = visitNodeInner(result.target, fn, ancestors) as Ast.Call['target'];
+			result.target = visitNodeInner(result.target, fn, ancestors);
 			for (let i = 0; i < result.args.length; i++) {
-				result.args[i] = visitNodeInner(result.args[i]!, fn, ancestors) as Ast.Call['args'][number];
+				result.args[i] = visitNodeInner(result.args[i]!, fn, ancestors);
 			}
 			break;
 		}
 		case 'index': {
-			result.target = visitNodeInner(result.target, fn, ancestors) as Ast.Index['target'];
-			result.index = visitNodeInner(result.index, fn, ancestors) as Ast.Index['index'];
+			result.target = visitNodeInner(result.target, fn, ancestors);
+			result.index = visitNodeInner(result.index, fn, ancestors);
 			break;
 		}
 		case 'prop': {
-			result.target = visitNodeInner(result.target, fn, ancestors) as Ast.Prop['target'];
+			result.target = visitNodeInner(result.target, fn, ancestors);
 			break;
 		}
 		case 'ns': {
 			for (let i = 0; i < result.members.length; i++) {
-				result.members[i] = visitNodeInner(result.members[i]!, fn, ancestors) as (typeof result.members)[number];
+				result.members[i] = visitNodeInner(result.members[i]!, fn, ancestors);
 			}
 			break;
 		}
@@ -173,50 +170,20 @@ function visitNodeInner(node: Ast.Node, fn: (node: Ast.Node, ancestors: Ast.Node
 		case 'neq':
 		case 'and':
 		case 'or': {
-			result.left = visitNodeInner(result.left, fn, ancestors) as (
-				Ast.Pow |
-				Ast.Mul |
-				Ast.Div |
-				Ast.Rem |
-				Ast.Add |
-				Ast.Sub |
-				Ast.Lt |
-				Ast.Lteq |
-				Ast.Gt |
-				Ast.Gteq |
-				Ast.Eq |
-				Ast.Neq |
-				Ast.And |
-				Ast.Or
-			)['left'];
-			result.right = visitNodeInner(result.right, fn, ancestors) as (
-				Ast.Pow |
-				Ast.Mul |
-				Ast.Div |
-				Ast.Rem |
-				Ast.Add |
-				Ast.Sub |
-				Ast.Lt |
-				Ast.Lteq |
-				Ast.Gt |
-				Ast.Gteq |
-				Ast.Eq |
-				Ast.Neq |
-				Ast.And |
-				Ast.Or
-			)['right'];
+			result.left = visitNodeInner(result.left, fn, ancestors);
+			result.right = visitNodeInner(result.right, fn, ancestors);
 			break;
 		}
 
 		case 'fnTypeSource': {
 			for (let i = 0; i < result.params.length; i++) {
-				result.params[i] = visitNodeInner(result.params[i]!, fn, ancestors) as Ast.FnTypeSource['params'][number];
+				result.params[i] = visitNodeInner(result.params[i]!, fn, ancestors);
 			}
 			break;
 		}
 		case 'unionTypeSource': {
 			for (let i = 0; i < result.inners.length; i++) {
-				result.inners[i] = visitNodeInner(result.inners[i]!, fn, ancestors) as Ast.UnionTypeSource['inners'][number];
+				result.inners[i] = visitNodeInner(result.inners[i]!, fn, ancestors);
 			}
 			break;
 		}
diff --git a/test/parser.ts b/test/parser.ts
index c2588b01..fa386fa0 100644
--- a/test/parser.ts
+++ b/test/parser.ts
@@ -8,14 +8,14 @@ describe('CharStream', () => {
 	test.concurrent('char', async () => {
 		const source = 'abc';
 		const stream = new CharStream(source);
-		assert.strictEqual('a', stream.char);
+		assert.strictEqual('a', stream.char());
 	});
 
 	test.concurrent('next', async () => {
 		const source = 'abc';
 		const stream = new CharStream(source);
 		stream.next();
-		assert.strictEqual('b', stream.char);
+		assert.strictEqual('b', stream.char());
 	});
 
 	describe('prev', () => {
@@ -23,37 +23,37 @@ describe('CharStream', () => {
 			const source = 'abc';
 			const stream = new CharStream(source);
 			stream.next();
-			assert.strictEqual('b', stream.char);
+			assert.strictEqual('b', stream.char());
 			stream.prev();
-			assert.strictEqual('a', stream.char);
+			assert.strictEqual('a', stream.char());
 		});
 
 		test.concurrent('境界外には移動しない', async () => {
 			const source = 'abc';
 			const stream = new CharStream(source);
 			stream.prev();
-			assert.strictEqual('a', stream.char);
+			assert.strictEqual('a', stream.char());
 		});
 	});
 
 	test.concurrent('eof', async () => {
 		const source = 'abc';
 		const stream = new CharStream(source);
-		assert.strictEqual(false, stream.eof);
+		assert.strictEqual(false, stream.eof());
 		stream.next();
-		assert.strictEqual(false, stream.eof);
+		assert.strictEqual(false, stream.eof());
 		stream.next();
-		assert.strictEqual(false, stream.eof);
+		assert.strictEqual(false, stream.eof());
 		stream.next();
-		assert.strictEqual(true, stream.eof);
+		assert.strictEqual(true, stream.eof());
 	});
 
 	test.concurrent('EOFでcharを参照するとエラー', async () => {
 		const source = '';
 		const stream = new CharStream(source);
-		assert.strictEqual(true, stream.eof);
+		assert.strictEqual(true, stream.eof());
 		try {
-			stream.char;
+			stream.char();
 		} catch (e) {
 			return;
 		}
@@ -63,13 +63,13 @@ describe('CharStream', () => {
 	test.concurrent('CRは読み飛ばされる', async () => {
 		const source = 'a\r\nb';
 		const stream = new CharStream(source);
-		assert.strictEqual('a', stream.char);
+		assert.strictEqual('a', stream.char());
 		stream.next();
-		assert.strictEqual('\n', stream.char);
+		assert.strictEqual('\n', stream.char());
 		stream.next();
-		assert.strictEqual('b', stream.char);
+		assert.strictEqual('b', stream.char());
 		stream.next();
-		assert.strictEqual(true, stream.eof);
+		assert.strictEqual(true, stream.eof());
 	});
 });
 
@@ -79,7 +79,10 @@ describe('Scanner', () => {
 		return stream;
 	}
 	function next(stream: Scanner, kind: TokenKind, pos: TokenPosition, opts: { hasLeftSpacing?: boolean, value?: string }) {
-		assert.deepStrictEqual(stream.getToken(), TOKEN(kind, pos, opts));
+		if (opts.hasLeftSpacing == null) {
+			opts.hasLeftSpacing = false;
+		}
+		assert.deepStrictEqual(stream.getToken(), TOKEN(kind as any, pos, opts as any));
 		stream.next();
 	}
 
@@ -139,7 +142,7 @@ describe('Scanner', () => {
 	test.concurrent('lookahead', async () => {
 		const source = '@abc() { }';
 		const stream = init(source);
-		assert.deepStrictEqual(stream.lookahead(1), TOKEN(TokenKind.Identifier, { line: 1, column: 2 }, { value: 'abc' }));
+		assert.deepStrictEqual(stream.lookahead(1), TOKEN(TokenKind.Identifier, { line: 1, column: 2 }, { hasLeftSpacing: false, value: 'abc' }));
 		next(stream, TokenKind.At, { line: 1, column: 1 }, { });
 		next(stream, TokenKind.Identifier, { line: 1, column: 2 }, { value: 'abc' });
 		next(stream, TokenKind.OpenParen, { line: 1, column: 5 }, { });
diff --git a/unreleased/ast-node-for-type.md b/unreleased/ast-node-for-type.md
new file mode 100644
index 00000000..f89a69b0
--- /dev/null
+++ b/unreleased/ast-node-for-type.md
@@ -0,0 +1 @@
+- **Breaking Change** For Hosts: Ast.Forの型がより厳格になりました。