fn-impl-reg
使用函数实现正则表达式
// a
const alpha = ( ch ) => ( str , index , succ , fail ) =>
ch === str [ index ] ? succ ( str , index + 1 ) : fail ( str , index ) ;
// ""
const epsilon = ( ) => ( str , index , succ , fail ) => succ ( str , index ) ;
// ab
const concat = ( head , tail ) => ( str , index , succ , fail ) =>
head ( str , index , ( s , i ) => tail ( s , i , succ , fail ) , fail ) ;
//
