Streams and objects
The ls operator lists files, like any Linux shell. But there are important differences. The Linux ls executable prints strings describing files, either multiple file names per line; or, if you specify the -l flag, then one file per line, with each line including file attributes such as mode, modification time, owner, group, and others. I.e., the printing and formatting logic is part of the ls executable.
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By contrast, marcel's ls operator generates a stream of File objects, and has no responsibility for printing or formatting -- if you run help ls you will see no such options.
The stream of File objects generated by ls can be passed to the output operator, write:
M 0.18.3 jao@loon ~/git/marcel/marcel$ ls object | write
drwxr-xr-x jao jao 4096 2023 Sep 10 12:32:29 .
-rw-r--r-- jao jao 652 2020 May 10 15:41:11 __init__.py
drwxrwxr-x jao jao 4096 2023 Oct 25 17:30:55 __pycache__
-rw-rw-r-- jao jao 3120 2023 Sep 07 20:53:42 cluster.py
-rw-rw-r-- jao jao 4793 2023 Oct 25 13:53:07 color.py
-rw-rw-r-- jao jao 2660 2020 Nov 19 14:12:20 db.py
-rw-r--r-- jao jao 1436 2022 Nov 29 11:33:51 error.py
-rw-rw-r-- jao jao 8763 2023 Oct 25 13:53:07 file.py
-rw-r--r-- jao jao 1707 2020 Aug 11 19:24:19 historyrecord.py
-rw-r--r-- jao jao 2548 2020 Nov 06 10:28:57 process.py
-rw-r--r-- jao jao 856 2020 Aug 11 19:24:19 renderable.py
The net effect is a listing very much like what you would see by running ls -l from bash.
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You can almost always omit explicitly using the write operator. Marcel appends write to your command line, if you don't specify it yourself. So you can get the same listing of files by just writing ls. You do need to specify write explicitly if you want to write to a file, instead of to the console, or to control formatting. For example, to save the ls result in /tmp/files you could do the following:
M 0.18.3 jao@loon ~/git/marcel/marcel$ ls object | write /tmp/files
There is no output to the console, because the output from ls was written to /tmp/files. (The same command could also be written as ls object > /tmp/files, as in bash.)