easy lexer

easyLexer.go

package main

/*
简单的词法分析器演示
number: [0-9]+
identifier: [a-zA-Z_]
*/
/*
0 start
1 identifer
2 number
*/
var state = 0
var cache []rune

func main() {
	var input = "123 abc 13 ag"
	cache = make([]rune, 0)
	for _, c := range input {
		if state == 0 {
			if c == ' ' {
				continue
			} else if ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || c == '_' {
				state = 1
				cache = append(cache, c)
				continue
			} else if '0' <= c && c <= '9'{
				state =2
				cache = append(cache, c)
				continue
			}else{
				println("Error,unrecognized character "+ string(c))
				break
			}
		} else if state == 1 {
			if c == ' '{
				state = 0
				println("token: " + string(cache))
				cache=make([]rune,0)
				continue
			}else if ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || c == '_'{
				cache = append(cache, c)
				continue
			}else if '0' <= c && c <= '9'{
				println("Error,unrecognized character "+ string(c))
				break;
			}
		}else if state ==2 {
			if c == ' '{
				state = 0
				println("token: " + string(cache))
				cache=make([]rune,0)
				continue
			}else if ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || c == '_'{
				println("Error,unrecognized character "+ string(c))
				break;
			}else if '0' <= c && c <= '9'{
				cache = append(cache, c)
				continue
			}
		}
	}
	if len(cache) > 0 {
		println("token: " + string(cache))
	}
}