I’d like to get some feedback on at least one aspect of Nu before anyone else becomes dependent on it: the use of sigils to indicate the type of a name binding.
As I’ve described Nu, it uses special prefixes on names to signal how they are bound. The ones I chose were stolen directly from Ruby (talent imitates, genius steals), and are as follows:
| $ | indicates a global variable. |
| @ | indicates an instance variable. |
| @@ | indicates a class variable (not yet, but likely). |
I think those are probably all fine, and if anyone doesn’t like them, I can always blame Matz :-). But I added one more, and I’m having second thoughts about my choice:
| __ | indicates a gensym. |
I’ve been having doubts about this after revisiting some python code, where double-underscores are used all over the place, and after considering that underscores and double-underscores show up a lot in compiled C object files. So to avoid ambiguity, I’d like to pick something completely different to be the gensym sigil. My current favorite alternative is to use a two-caret prefix, making ^^foo a gensym.
Any comments or other suggestions?
p.s. A gensym is a “generated symbol” that is used in a macro expansion to avoid conflicts between names. In the macro below, __x is a gensym name. Each time the factorial macro is expanded, the gensym name is replaced with an automatically-generated name that is guaranteed to be unique.
(macro factorial
(set __x (eval (car margs)))
(if (== __x 0)
(then 1)
(else (* (factorial (- __x 1)) __x))))
9 comments ↓
I like the Ruby variable prefixes, so no complaints from me.
As for the gensym, how about a hash as a prefix? Assuming that doesn’t conflict with anything.
x
It’s only one character, which is nicer than the two caret prefix I think.
That big x is out-of-control Textile markup.
Here’s a hash-x:
I think it’s a bit too close to this:#x.#{x}, which if placed inside a string will cause the value of x to be interpolated into the string.But side by side, maybe
#xdoes beat^^x.Oops, a hash is a comment character, which is useful when it’s time to write Nu scripts that begin with:
#!/usr/bin/env nushYeah I’m fine with the Ruby sigils. I also think, given the limited context, that either _ or ^^ is a reasonable choice for gensyms although looking at both in textmate I think I find _ to be slighter easier on the eye.
(p.s. I couldn’t seem to escape those underscores properly to avoid textile formatting).
The Ruby sigils are fine. I personally prefer the double underscores to ^^ or # for gensyms. I wouldn’t worry about double underscored names in C bleeding into Nu via FFI. IIRC, the double underscore is reserved for implementers of the standard library and should never be a part of a C library’s public interface.
Why not reuse an existing sigil, $—e.g., $$ means a gensym. Presumably you’re not using $$ to mean PID like Ruby does.
Textile!
Well, if a hash prefix is out, then the double dollar sign is the go.
It’s immediately recognisable and doesn’t clash with anything else. Does it imply a relationship to the global variables though? Much like the double @ in a class variable implies a relationship to an instance variable.
One thing that I don’t like about the double dollar sign is its lack of a relationship with the single dollar sign. So since no alternative seems any better, I’m going to stick with the Textile-unfriendly
__(To beat Textile, wrap it in <code> tags).Thanks for all of your comments on this.
How about question mark (?x) ?