return withFunKind(kind, () => {
		// TODO:ES6 use `...`f
		const nArgs = new LiteralNumber(args.length)
		const opDeclareRest = opMap(opRestArg, rest =>
			makeDeclare(rest, new CallExpression(arraySliceCall, [idArguments, nArgs])))
		const argChecks = opIf(compileOptions.checks, () =>
			flatMapOps(args, opTypeCheckForLocalDeclare))

		const opDeclareThisAst = opIf(opDeclareThis !== null && !dontDeclareThis, () =>
			declareLexicalThis)

		const lead = cat(opDeclareRest, opDeclareThisAst, argChecks, leadStatements)

		const body = () => transpileBlock(block, {lead, opReturnType})
		const argAsts = args.map(transpileLocalDeclare)
		const id = opMap(verifyResults.opName(_), identifier)

		switch (kind) {
			case Funs.Async: {
				const plainBody = transpileBlock(block, {opReturnType})
				const genFunc = new FunctionExpression(null, [], plainBody, {generator: true})
				const ret = new ReturnStatement(msCall('async', genFunc))
				return new FunctionExpression(id, argAsts, new BlockStatement(cat(lead, ret)))
			}
			case Funs.Generator:
				return new FunctionExpression(id, argAsts, body(), {generator: true})
			case Funs.Plain:
				// TODO:ES6 Should be able to use rest args in arrow function
				return id === null && opDeclareThis === null && opDeclareRest === null ?
					new ArrowFunctionExpression(argAsts, body()) :
					new FunctionExpression(id, argAsts, body())
			default:
				throw new Error(String(kind))
		}
	})

	return opIf(!localDeclare.isLazy, () =>
		opMap(localDeclare.opType, type =>
			new ExpressionStatement(msCall(
				'checkInstance',
				transpileVal(type),
				accessLocalDeclare(localDeclare),
				new LiteralString(localDeclare.name)))))

export function transpileYieldLikeNoLoc(_: YieldLike): Expression {
	if (_ instanceof Yield)
		return new YieldExpression(opMap(_.opValue, transpileVal))
	else if (_ instanceof YieldTo)
		return new YieldDelegateExpression(transpileVal(_.value))
	else
		throw new Error(_.constructor.name)
}

function parseClassHeader(tokens: Tokens)
	: {opFields: Op<Array<Field>>, opSuperClass: Op<Val>, traits: Array<Val>} {
	const [fieldsTokens, [extendsTokens, traitTokens]] =
		tokens.getKeywordSections(Kw.Extends, Kw.Trait)
	return {
		opFields: opIf(!fieldsTokens.isEmpty(), () => fieldsTokens.map(_ => {
			const {name, opType, kind} = parseLocalParts(_)
			check(kind === LocalDeclares.Eager, _.loc, _ => _.todoLazyField)
			return new Field(_.loc, name, opType)
		})),
		opSuperClass: opMap(extendsTokens, parseExpr),
		traits: caseOp(traitTokens, parseExprParts, () => [])
	}
}

export function opKeywordFromName(loc: Loc, name: string): Op<Keyword> {
	// I tried a switch statement, but using a map of closures was actually faster.
	return opMap(nameToKeywordCreator.get(name), _ => _(loc))
}

export default function parseCase(tokens: Tokens): Case {
	const [before, block] = beforeAndBlock(tokens)
	const opCased = opMap(opParseExpr(before), _ => AssignSingle.focus(_.loc, _))
	const {parts, opElse} = parseCaseParts(block)
	return new Case(tokens.loc, opCased, parts, opElse)
}