parser
*******

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.