routine Foo( a = 0, b = "" )=>[?]
{
	io.writeln( "Foo():", a );
	return yield( 2 * a, "by Foo()" );
}

routine Bar( a = 0, b = "" )=>[?]
{
	io.writeln( "Bar():", a, b );
	( r, s ) = Foo( a + 1, b );
	io.writeln( "Bar():", r, s );
	( r, s ) = yield( a + 100, b );
	io.writeln( "Bar():", r, s );
	return a, "ended";
}

global co = Bar::( 100, "AA" );



@[test(code_01)]

io.writeln( "Main: ", co() );

@[test(code_01)]
@[test(code_01)]
Bar(): 100 AA
Foo(): 101
Main:  ( 202, "by Foo()" )
@[test(code_01)]



@[test(code_01)]

io.writeln( "Main: ", co( 200, "XX" ) );

@[test(code_01)]
@[test(code_01)]
Bar(): 200 XX
Main:  ( 200, "AA" )
@[test(code_01)]



@[test(code_01)]

io.writeln( "Main: ", co( 300, "YY" ) );

@[test(code_01)]
@[test(code_01)]
Bar(): 300 YY
Main:  ( 100, "ended" )
@[test(code_01)]



@[test(code_01)]

# coroutine has been finished, the following will rise an exception.
io.writeln( "Main: ", co( 400, "ZZ" ) );

@[test(code_01)]
@[test(code_01)]
{{Exception.Warning}} .* {{coroutine execution is finished}}
@[test(code_01)]



@[test(code_01)]
routine Test()
{
	yield( 1 )  # Error: cannot yield;
}
@[test(code_01)]
@[test(code_01)]
{{Cannot yield from normal function}} .* {{ERROR}} .* {{At line}}
@[test(code_01)]



@[test(code_01)]
routine Test()
{
	return 1
}
co2 = Test::()  # Error???
@[test(code_01)]
@[test(code_01)]
@[test(code_01)]