file string-expression (is | isnt) writable

This operator succeeds if the file named by the string expression exists and is writable by the OmniMark program, or if it does not exist but can be created.

For example, the following code uses the file...is writable test to make sure that the file is writable:

  find-start
    do when file "myfile.out" is writable
      open out as file "myfile.out"
    else
      put #error "Cannot write to file 'myfile.out'.%n"
      halt with 1
    done