Sure, but why would you want to?
I/O for stream files/flat files in the IFS is done using APIs, which are much easier to deal with in a language like RPG or COBOL. Use the right tool for the job.
As of V5R4, ILE CL handles streamfile I/O almost the same as ILE RPG, C or COBOL. It’s probably much easier to write in CL, but the APIs will be the same ones. Use the open(), write() and close() APIs. These are listed and described in the <a href=”http://publib.boulder.ibm.com/infocenter/iseries/v5r4/topic/apis/unix2.htm”>Integrated File System APIs</a> topic.
Although these can be easier in ILE CL than other languages, it should probably be done for proofs-of-concept or prototyping or learning, rather than for significant production programming. ILE CL can only include a single procedure in each source module. For some purposes, that is okay for CL.