diff --git a/src/generators/Generator.ts b/src/generators/Generator.ts
index 18135a3045..9e6d2c0a76 100644
--- a/src/generators/Generator.ts
+++ b/src/generators/Generator.ts
@@ -10,15 +10,34 @@ import getIntro from './shared/utils/getIntro';
 import getOutro from './shared/utils/getOutro';
 import processCss from './shared/processCss';
 import annotateWithScopes from '../utils/annotateWithScopes';
+import { Node, Parsed, CompileOptions } from '../../interfaces';
 
 const test = typeof global !== 'undefined' && global.__svelte_test;
 
 export default class Generator {
-	source: string
-	name: string
-	// TODO all the rest...
-
-	constructor ( parsed, source: string, name: string, options ) {
+	parsed: Parsed;
+	source: string;
+	name: string;
+	options: CompileOptions;
+
+	imports: Node[];
+	helpers: Set<string>;
+	components: Set<string>;
+	events: Set<string>;
+	transitions: Set<string>;
+	importedComponents: Map<string, string>;
+
+	bindingGroups: string[];
+	expectedProperties: Set<string>;
+	css: string;
+	cssId: string;
+	usesRefs: boolean;
+
+	importedNames: Set<string>;
+	aliases: Map<string, string>;
+	usedNames: Set<string>;
+
+	constructor ( parsed: Parsed, source: string, name: string, options: CompileOptions ) {
 		this.parsed = parsed;
 		this.source = source;
 		this.name = name;
@@ -46,19 +65,19 @@ export default class Generator {
 		// Svelte's builtin `import { get, ... } from 'svelte/shared.ts'`;
 		this.importedNames = new Set();
 		this.aliases = new Map();
-		this._usedNames = new Set( [ name ] );
+		this.usedNames = new Set( [ name ] );
 	}
 
-	addSourcemapLocations ( node ) {
+	addSourcemapLocations ( node: Node ) {
 		walk( node, {
-			enter: node => {
+			enter: ( node: Node ) => {
 				this.code.addSourcemapLocation( node.start );
 				this.code.addSourcemapLocation( node.end );
 			}
 		});
 	}
 
-	alias ( name ) {
+	alias ( name: string ) {
 		if ( !this.aliases.has( name ) ) {
 			this.aliases.set( name, this.getUniqueName( name ) );
 		}
@@ -66,10 +85,10 @@ export default class Generator {
 		return this.aliases.get( name );
 	}
 
-	contextualise ( block, expression, context, isEventHandler ) {
+	contextualise ( block, expression: Node, context, isEventHandler ) {
 		this.addSourcemapLocations( expression );
 
-		const usedContexts = [];
+		const usedContexts: string[] = [];
 
 		const { code, helpers } = this;
 		const { contexts, indexes } = block;
@@ -80,7 +99,7 @@ export default class Generator {
 		const self = this;
 
 		walk( expression, {
-			enter ( node, parent, key ) {
+			enter ( node: Node, parent: Node, key: string ) {
 				if ( /^Function/.test( node.type ) ) lexicalDepth += 1;
 
 				if ( node._scope ) {
@@ -142,7 +161,7 @@ export default class Generator {
 				}
 			},
 
-			leave ( node ) {
+			leave ( node: Node ) {
 				if ( /^Function/.test( node.type ) ) lexicalDepth -= 1;
 				if ( node._scope ) scope = scope.parent;
 			}
@@ -159,12 +178,12 @@ export default class Generator {
 		if ( expression._dependencies ) return expression._dependencies;
 
 		let scope = annotateWithScopes( expression );
-		const dependencies = [];
+		const dependencies: string[] = [];
 
 		const generator = this; // can't use arrow functions, because of this.skip()
 
 		walk( expression, {
-			enter ( node, parent ) {
+			enter ( node: Node, parent: Node ) {
 				if ( node._scope ) {
 					scope = node._scope;
 					return;
@@ -184,7 +203,7 @@ export default class Generator {
 				}
 			},
 
-			leave ( node ) {
+			leave ( node: Node ) {
 				if ( node._scope ) scope = scope.parent;
 			}
 		});
@@ -278,11 +297,11 @@ export default class Generator {
 		};
 	}
 
-	getUniqueName ( name ) {
+	getUniqueName ( name: string ) {
 		if ( test ) name = `${name}$`;
 		let alias = name;
-		for ( let i = 1; reservedNames.has( alias ) || this.importedNames.has( alias ) || this._usedNames.has( alias ); alias = `${name}_${i++}` );
-		this._usedNames.add( alias );
+		for ( let i = 1; reservedNames.has( alias ) || this.importedNames.has( alias ) || this.usedNames.has( alias ); alias = `${name}_${i++}` );
+		this.usedNames.add( alias );
 		return alias;
 	}
 
@@ -291,13 +310,13 @@ export default class Generator {
 		return name => {
 			if ( test ) name = `${name}$`;
 			let alias = name;
-			for ( let i = 1; reservedNames.has( alias ) || this.importedNames.has( alias ) || this._usedNames.has( alias ) || localUsedNames.has( alias ); alias = `${name}_${i++}` );
+			for ( let i = 1; reservedNames.has( alias ) || this.importedNames.has( alias ) || this.usedNames.has( alias ) || localUsedNames.has( alias ); alias = `${name}_${i++}` );
 			localUsedNames.add( alias );
 			return alias;
 		};
 	}
 
-	parseJs ( ssr ) {
+	parseJs ( ssr: boolean = false ) {
 		const { source } = this;
 		const { js } = this.parsed;
 
diff --git a/src/generators/dom/Block.ts b/src/generators/dom/Block.ts
index b471b7f00f..0711d76344 100644
--- a/src/generators/dom/Block.ts
+++ b/src/generators/dom/Block.ts
@@ -1,8 +1,21 @@
 import CodeBuilder from '../../utils/CodeBuilder';
 import deindent from '../../utils/deindent.js';
+import { DomGenerator } from './index';
+import { Node } from '../../interfaces';
+
+export interface BlockOptions {
+	generator: DomGenerator
+	name: string
+	expression: Node
+	context: string
+}
 
 export default class Block {
-	constructor ( options ) {
+	generator: DomGenerator;
+	name: string;
+	expression: Node;
+
+	constructor ( options: BlockOptions ) {
 		this.generator = options.generator;
 		this.name = options.name;
 		this.expression = options.expression;
diff --git a/src/generators/dom/index.ts b/src/generators/dom/index.ts
index 4614712b90..d2d02ff14d 100644
--- a/src/generators/dom/index.ts
+++ b/src/generators/dom/index.ts
@@ -9,9 +9,16 @@ import visit from './visit';
 import shared from './shared';
 import Generator from '../Generator';
 import preprocess from './preprocess';
+import Block from './Block';
+import { Parsed, CompileOptions, Node } from '../../interfaces';
 
-class DomGenerator extends Generator {
-	constructor ( parsed, source, name, options ) {
+export class DomGenerator extends Generator {
+	blocks: Block[]
+	uses: Set<string>;
+	readonly: Set<string>;
+	metaBindings: string[];
+
+	constructor ( parsed: Parsed, source: string, name: string, options: CompileOptions ) {
 		super( parsed, source, name, options );
 		this.blocks = [];
 		this.uses = new Set();
@@ -22,7 +29,7 @@ class DomGenerator extends Generator {
 		this.metaBindings = [];
 	}
 
-	helper ( name ) {
+	helper ( name: string ) {
 		if ( this.options.dev && `${name}Dev` in shared ) {
 			name = `${name}Dev`;
 		}
@@ -33,7 +40,7 @@ class DomGenerator extends Generator {
 	}
 }
 
-export default function dom ( parsed, source, options ) {
+export default function dom ( parsed: Parsed, source: string, options: CompileOptions ) {
 	const format = options.format || 'es';
 	const name = options.name || 'SvelteComponent';
 
@@ -49,7 +56,7 @@ export default function dom ( parsed, source, options ) {
 
 	const block = preprocess( generator, state, parsed.html );
 
-	parsed.html.children.forEach( node => {
+	parsed.html.children.forEach( ( node: Node ) => {
 		visit( generator, block, state, node );
 	});
 
diff --git a/src/generators/dom/preprocess.ts b/src/generators/dom/preprocess.ts
index 7d26c5a2c0..1ea44a6855 100644
--- a/src/generators/dom/preprocess.ts
+++ b/src/generators/dom/preprocess.ts
@@ -1,12 +1,14 @@
 import Block from './Block';
 import { trimStart, trimEnd } from '../../utils/trim';
 import { assign } from '../../shared/index.js';
+import { DomGenerator } from './index';
+import { Node } from '../../interfaces';
 
-function isElseIf ( node ) {
+function isElseIf ( node: Node ) {
 	return node && node.children.length === 1 && node.children[0].type === 'IfBlock';
 }
 
-function getChildState ( parent, child ) {
+function getChildState ( parent, child = {} ) {
 	return assign( {}, parent, { name: null, parentNode: null }, child || {} );
 }
 
@@ -25,7 +27,7 @@ const elementsWithoutText = new Set([
 ]);
 
 const preprocessors = {
-	MustacheTag: ( generator, block, state, node ) => {
+	MustacheTag: ( generator: DomGenerator, block, state, node: Node ) => {
 		const dependencies = block.findDependencies( node.expression );
 		block.addDependencies( dependencies );
 
@@ -34,7 +36,7 @@ const preprocessors = {
 		});
 	},
 
-	RawMustacheTag: ( generator, block, state, node ) => {
+	RawMustacheTag: ( generator: DomGenerator, block, state, node: Node ) => {
 		const dependencies = block.findDependencies( node.expression );
 		block.addDependencies( dependencies );
 
@@ -44,7 +46,7 @@ const preprocessors = {
 		node._state = getChildState( state, { basename, name });
 	},
 
-	Text: ( generator, block, state, node ) => {
+	Text: ( generator: DomGenerator, block, state, node: Node ) => {
 		node._state = getChildState( state );
 
 		if ( !/\S/.test( node.data ) ) {
@@ -56,13 +58,13 @@ const preprocessors = {
 		node._state.name = block.getUniqueName( `text` );
 	},
 
-	IfBlock: ( generator, block, state, node ) => {
+	IfBlock: ( generator: DomGenerator, block, state, node: Node ) => {
 		const blocks = [];
 		let dynamic = false;
 		let hasIntros = false;
 		let hasOutros = false;
 
-		function attachBlocks ( node ) {
+		function attachBlocks ( node: Node ) {
 			const dependencies = block.findDependencies( node.expression );
 			block.addDependencies( dependencies );
 
@@ -113,7 +115,7 @@ const preprocessors = {
 		generator.blocks.push( ...blocks );
 	},
 
-	EachBlock: ( generator, block, state, node ) => {
+	EachBlock: ( generator: DomGenerator, block, state, node: Node ) => {
 		const dependencies = block.findDependencies( node.expression );
 		block.addDependencies( dependencies );
 
@@ -175,7 +177,7 @@ const preprocessors = {
 		}
 	},
 
-	Element: ( generator, block, state, node ) => {
+	Element: ( generator: DomGenerator, block, state, node: Node ) => {
 		const isComponent = generator.components.has( node.name ) || node.name === ':Self';
 
 		if ( isComponent ) {
@@ -193,9 +195,9 @@ const preprocessors = {
 			});
 		}
 
-		node.attributes.forEach( attribute => {
+		node.attributes.forEach( ( attribute: Node ) => {
 			if ( attribute.type === 'Attribute' && attribute.value !== true ) {
-				attribute.value.forEach( chunk => {
+				attribute.value.forEach( ( chunk: Node ) => {
 					if ( chunk.type !== 'Text' ) {
 						const dependencies = block.findDependencies( chunk.expression );
 						block.addDependencies( dependencies );
@@ -238,12 +240,12 @@ const preprocessors = {
 	}
 };
 
-function preprocessChildren ( generator, block, state, node, isTopLevel ) {
+function preprocessChildren ( generator: DomGenerator, block, state, node: Node, isTopLevel: boolean ) {
 	// glue text nodes together
-	const cleaned = [];
-	let lastChild;
+	const cleaned: Node[] = [];
+	let lastChild: Node;
 
-	node.children.forEach( child => {
+	node.children.forEach( ( child: Node ) => {
 		if ( child.type === 'Comment' ) return;
 
 		if ( child.type === 'Text' && lastChild && lastChild.type === 'Text' ) {
@@ -273,7 +275,7 @@ function preprocessChildren ( generator, block, state, node, isTopLevel ) {
 
 	lastChild = null;
 
-	cleaned.forEach( child => {
+	cleaned.forEach( ( child: Node ) => {
 		const preprocess = preprocessors[ child.type ];
 		if ( preprocess ) preprocess( generator, block, state, child );
 
@@ -292,7 +294,7 @@ function preprocessChildren ( generator, block, state, node, isTopLevel ) {
 	node.children = cleaned;
 }
 
-export default function preprocess ( generator, state, node ) {
+export default function preprocess ( generator: DomGenerator, state, node ) {
 	const block = new Block({
 		generator,
 		name: generator.alias( 'create_main_fragment' ),
diff --git a/src/generators/dom/visit.ts b/src/generators/dom/visit.ts
index e37a8c7fd8..1443a32049 100644
--- a/src/generators/dom/visit.ts
+++ b/src/generators/dom/visit.ts
@@ -1,6 +1,9 @@
 import visitors from './visitors/index';
+import { DomGenerator } from './index';
+import Block from './Block';
+import { Node } from '../../interfaces';
 
-export default function visit ( generator, block, state, node ) {
+export default function visit ( generator: DomGenerator, block: Block, state, node: Node ) {
 	const visitor = visitors[ node.type ];
 	visitor( generator, block, state, node );
 }
\ No newline at end of file
diff --git a/src/generators/dom/visitors/YieldTag.ts b/src/generators/dom/visitors/YieldTag.ts
index 81dcb3ad53..ebebb78557 100644
--- a/src/generators/dom/visitors/YieldTag.ts
+++ b/src/generators/dom/visitors/YieldTag.ts
@@ -1,4 +1,7 @@
-export default function visitYieldTag ( generator, block, state ) {
+import { DomGenerator } from '../index';
+import Block from '../Block';
+
+export default function visitYieldTag ( generator: DomGenerator, block: Block, state ) {
 	const parentNode = state.parentNode || block.target;
 
 	( state.parentNode ? block.builders.create : block.builders.mount ).addLine(
diff --git a/src/generators/shared/processCss.ts b/src/generators/shared/processCss.ts
index 91ca055d31..b83630d756 100644
--- a/src/generators/shared/processCss.ts
+++ b/src/generators/shared/processCss.ts
@@ -1,6 +1,8 @@
+import { Parsed, Node } from '../../interfaces';
+
 const commentsPattern = /\/\*[\s\S]*?\*\//g;
 
-export default function processCss ( parsed, code ) {
+export default function processCss ( parsed: Parsed, code ) {
 	const css = parsed.css.content.styles;
 	const offset = parsed.css.content.start;
 
@@ -8,9 +10,9 @@ export default function processCss ( parsed, code ) {
 
 	const keyframes = new Map();
 
-	function walkKeyframes ( node ) {
+	function walkKeyframes ( node: Node ) {
 		if ( node.type === 'Atrule' && node.name.toLowerCase() === 'keyframes' ) {
-			node.expression.children.forEach( expression => {
+			node.expression.children.forEach( ( expression: Node ) => {
 				if ( expression.type === 'Identifier' ) {
 					const newName = `svelte-${parsed.hash}-${expression.name}`;
 					code.overwrite( expression.start, expression.end, newName );
@@ -26,8 +28,8 @@ export default function processCss ( parsed, code ) {
 
 	parsed.css.children.forEach( walkKeyframes );
 
-	function transform ( rule ) {
-		rule.selector.children.forEach( selector => {
+	function transform ( rule: Node ) {
+		rule.selector.children.forEach( ( selector: Node ) => {
 			const start = selector.start - offset;
 			const end = selector.end - offset;
 
@@ -50,11 +52,11 @@ export default function processCss ( parsed, code ) {
 			code.overwrite( start + offset, end + offset, transformed );
 		});
 
-		rule.block.children.forEach( block => {
+		rule.block.children.forEach( ( block: Node ) => {
 			if ( block.type === 'Declaration' ) {
 				const property = block.property.toLowerCase();
 				if ( property === 'animation' || property === 'animation-name' ) {
-					block.value.children.forEach( block => {
+					block.value.children.forEach( ( block: Node ) => {
 						if ( block.type === 'Identifier' ) {
 							const name = block.name;
 							if ( keyframes.has( name ) ) {
@@ -67,7 +69,7 @@ export default function processCss ( parsed, code ) {
 		});
 	}
 
-	function walk ( node ) {
+	function walk ( node: Node ) {
 		if ( node.type === 'Rule' ) {
 			transform( node );
 		} else if ( node.type === 'Atrule' && node.name.toLowerCase() === 'keyframes' ) {
diff --git a/src/generators/shared/utils/walkHtml.ts b/src/generators/shared/utils/walkHtml.ts
index 39568cd742..ad5d826e1a 100644
--- a/src/generators/shared/utils/walkHtml.ts
+++ b/src/generators/shared/utils/walkHtml.ts
@@ -1,12 +1,14 @@
-export default function walkHtml ( html, visitors ) {
-	function visit ( node ) {
+import { Node } from '../../../interfaces';
+
+export default function walkHtml ( html: Node, visitors ) {
+	function visit ( node: Node ) {
 		const visitor = visitors[ node.type ];
 		if ( !visitor ) throw new Error( `Not implemented: ${node.type}` );
 
 		if ( visitor.enter ) visitor.enter( node );
 
 		if ( node.children ) {
-			node.children.forEach( child => {
+			node.children.forEach( ( child: Node ) => {
 				visit( child );
 			});
 		}
diff --git a/src/index.ts b/src/index.ts
index 19c5b41930..b0fd1e7b30 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -4,16 +4,16 @@ import generate from './generators/dom/index';
 import generateSSR from './generators/server-side-rendering/index';
 import { assign } from './shared/index.js';
 import { version } from '../package.json';
-import { Parsed } from './interface';
+import { Parsed, CompileOptions, Warning } from './interfaces';
 
-function normalizeOptions ( options ) {
-	return assign( {
+function normalizeOptions ( options: CompileOptions ) :CompileOptions {
+	return assign({
 		generate: 'dom',
 
 		// a filename is necessary for sourcemap generation
 		filename: 'SvelteComponent.html',
 
-		onwarn: warning => {
+		onwarn: ( warning: Warning ) => {
 			if ( warning.loc ) {
 				console.warn( `(${warning.loc.line}:${warning.loc.column}) – ${warning.message}` ); // eslint-disable-line no-console
 			} else {
@@ -21,13 +21,13 @@ function normalizeOptions ( options ) {
 			}
 		},
 
-		onerror: error => {
+		onerror: ( error: Error ) => {
 			throw error;
 		}
 	}, options );
 }
 
-export function compile ( source, _options ) {
+export function compile ( source: string, _options: CompileOptions ) {
 	const options = normalizeOptions( _options );
 
 	let parsed: Parsed;
diff --git a/src/interfaces.ts b/src/interfaces.ts
index 897c50b625..0ffe275064 100644
--- a/src/interfaces.ts
+++ b/src/interfaces.ts
@@ -23,4 +23,23 @@ export interface Parsed {
 	html: Node;
 	css: Node;
 	js: Node;
+}
+
+export interface Warning {
+	loc?: {line: number, column: number, pos: number};
+	message: string
+	filename?: string
+	toString: () => string
+}
+
+export interface CompileOptions {
+	format?: string;
+	name?: string;
+	filename?: string;
+
+	dev?: boolean;
+	shared?: boolean | string;
+
+	onerror?: (error: Error) => void
+	onwarn?: (warning: Warning) => void
 }
\ No newline at end of file
diff --git a/src/validate/index.ts b/src/validate/index.ts
index b09374fce1..891132d23b 100644
--- a/src/validate/index.ts
+++ b/src/validate/index.ts
@@ -3,7 +3,7 @@ import validateHtml from './html/index';
 import { getLocator, Location } from 'locate-character';
 import getCodeFrame from '../utils/getCodeFrame';
 import CompileError from '../utils/CompileError'
-import { Node, Parsed } from '../interfaces';
+import { Node, Parsed, CompileOptions, Warning } from '../interfaces';
 
 class ValidationError extends CompileError {
 	constructor ( message: string, template: string, index: number, filename: string ) {
@@ -27,7 +27,7 @@ export class Validator {
 	helpers: Map<string, Node>;
 	transitions: Map<string, Node>;
 
-	constructor ( parsed: Parsed, source: string, options: { onwarn, name?: string, filename?: string } ) {
+	constructor ( parsed: Parsed, source: string, options: CompileOptions ) {
 		this.source = source;
 		this.filename = options !== undefined ? options.filename : undefined;
 
@@ -64,7 +64,9 @@ export class Validator {
 	}
 }
 
-export default function validate ( parsed: Parsed, source: string, { onerror, onwarn, name, filename } ) {
+export default function validate ( parsed: Parsed, source: string, options: CompileOptions ) {
+	const { onwarn, onerror, name, filename } = options;
+
 	try {
 		if ( name && !/^[a-zA-Z_$][a-zA-Z_$0-9]*$/.test( name ) ) {
 			const error = new Error( `options.name must be a valid identifier` );