我在Pig中遇到错误

Question

A1 = LOAD'/home/sawanvijay/POC/IMDB.txt';
A2 = FOREACH A1 GENERATE $0;
A3 = FOREACH A2 GENERATE TOKENIZE($0);
A4= FOREACH A3 GENERATE REPLACE($0,'([^a-zA-Z\\s]+)',' ');
A5 = FOREACH A4 GENERATE FLATTEN(TOKENIZE($0));

运行命令时：

DUMP A4;

显示错误的Pig中的

：

ERROR org.apache.pig.tools.grunt.Grunt - ERROR 1045: 
<line 32, column 24> Could not infer the matching function for 
   org.apache.pig.builtin.REPLACE as multiple or none of them fit. 
   Please use an explicit cast.

logfile 的详细信息：/home/sawanvijay/pig_1452747154040.log

请告诉我这是什么问题？