parse, setstream
simple primitive position, nextchar, skip, goto
terminal matchers char, eos, letter,
compount matchers MatcerSequence, MatcherOr, Repeater may, parallel, any, some, times, times_more, times_less, seplist, seplist_more, seplist_less
null word nullword
compare with definite clause grammar more intuitive, more efficient, more expressive., easier to be read and written
compare with antlr.
compare with lex/yacc
compare with pyparsing，spark，ply，lepl etc.