clean gramf  api
tweak
make single_extend_statement a record
refactoring
with  a new DDSL local_extend
tweak
merge
rename a module
move ast_basic to main
make configuration correct
simplify the generator
better error message for lexer generator
bind also to be a  path
tweak bind path note that bind path is very useful for debugging,
but it is not robust enough to do serious code generation
tweak the lexer code generator
tweak the code generator
tweak
simplify
when mem_size is zero -- there is no need to create lex_mem
tweak --- ready to compile to string directly