Rebol cd requires no %?

Question

I'm using Rebol/Core 278-3.1 on Win-7 64-bit, launched from standard windows command shell. And I'm wondering how to explain to my young friend (a web designer by background) that the interpreter's CD command does not require the %.

It reminds me of DOS not needing a space after cd. The REPL is not a shell, so why make this shortcut as if it were a shell? Why is a string name of a directory treated as a word when no such word has been set? Does it not make code needlessly ambiguous at a first glance?

(Think as if this is your FIRST programming language experience ... not as an old user of ls cd mv in unix shells.)

Even if a word is set, that word is ignored by cd unless a get-word is used ... example would be:

dir %tests

and

dir tests:

"complete" where cd tests acts as if there is no word with get-word :tests

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Note: Saphirion R3 has the following behavior : if I set a word to a dir name but in upper-case, the get-word moves me to that dir and shows it in that incorrect upper-case. But there is no dir with that name. I believe that the cd should have given an error. Surely as a matter of unicode and compliance with the linux-like world .. or is this only working on Windows ? Off I go to my Virtual Box with ubuntu and Syllable ...

Answer 1

You can have a look at the source of the cd function by writing

source cd

There you can find that for convenience, other datatypes are converted to file.

"Why is a string name of a dir treated as a word when no such word has been set?"

Rebol recognizes words by syntax allowing symbolic programming. It does not matter at all whether a word has been set or not to be recognized as a word.

"[If] I set a word to a dir name but in upper-case, the get-word moves me to that dir and shows it in that incorrect upper-case"

Some operating systems (such as Windows) try to be case-insensitive, assuming that this is more convenient for humans.

Rebol string handling is also case-insensitive by default for the same reason.

"Did anyone ever suggest that chdir could have all convenience and quirks and that cd expect a file correctly named ?"

That is essentially what happened but in a different manner. There is a change-dir function which insists on proper (file!) datatype, while the cd function is a "convenience shortcut".

Answer 2

You say "the REPL is not a shell". I totally agree. On a related note, I'm adamantly opposed to:

append [x y z] q

...appearing to crash the interpreter by invoking the shortcut for quit. It's an easy mistake to make. And I feel it's penny-wise and pound-foolish to do similar shortcuts that you have noticed in the core interpreter. Rebol is a literate, English-like language that reads clearly... and things like LS and CD do not belong in the core. They should be part of a shell dialect, if anything.

Should a dialect author should be able to treat words as strings even if the domain of the legal words doesn't map to the range of the legal strings? I think it should be allowed, but I agree it sets a poor precedent in the shipping executable.