I'm trying to write to a file in Common Lisp, but I keep getting a "file is not a stream" error:
[1]> (open "file.txt" :direction :output :if-does-not-exist :create :if-exists :supersede)
#<output buffered file-stream character #P"file.txt">
[2]> (princ 'Hello "file.txt")
*** - princ: argument "file.txt" is not a stream
Even attempting to close the file returns an error:
[4]> (close "file.txt")
*** - no-applicable-method: When calling #<standard-generic-function close>
with arguments ("file.txt"), no method is applicable.
The file was properly created, so I thought it might be a permissions issue, but that doesn't seem to be it. I've Googled this error without any luck so far. Does anyone know what I am doing wrong? Thank you.
PS: I'm running Linux Mint 17.3 Rosa with CLISP 2.49 (2010-07-07)
To use open files, you must save the return value of open and uses it as the second argument to princ. You must also use that same return value as an argument to close.
This is usually done with the convenience macro with-open-file.
The files chapter of Practical Common Lisp shows how to use these and other functions and macros.