change the parser
add YieldStatement class
add a test
add new statement classes for code transformation
update function definition analysis to check IS_GENERATOR flag
set parser to template class defs
cleanup
add the built-in interface for generator stuff
add code transformation stage to the compiler
fix completion tests since two new built-in classes were added
remove todo flag from the test of generator
move tests for generator to t/generator
add another test
fix a bug in for-statement transformation
add some tests
support nested generator
add a test
add tests
fix a bug in transform of switch statement
fix a bug that $generatorN was not declared