TclinaPickle - 2012-07-05 14:51:06
That Tcl is a toy language is not a misperception, but a patently obvious observation by a very, very large number of programmers.
I've been using it against my will for the last few months, and recently discovered, to my complete shock, that braces in comments are syntactically significant.
So I google it and find all these very helpful posts from Tclers helping newbies to understand why.
The fact that braces in comments are syntactically significant is not something I want explained to me. I want it to behave in a reasonable way. It's a fucking comment and I want the interpreter to ignore it, for fuck's sake!
Tcl is little more than an extremely poor implementation of Lisp.
AMG: Tcl is basically several languages stacked on top of each other. The outer language doesn't know what a comment is; it only knows how to match up braces and quotes and stuff to form a list of words. Only when that's done do things get passed to the next level language: command dispatch, which does know comments. Then each command forms yet again its own language, e.g. [expr]. What you're suggesting is to make the brace matcher recognize comments. FB and I have proposed this too, and I hope to further develop this idea (and others) at the next Tcl/Tk conference. More on this in a second.
However, saying that comments which don't work reliably (i.e. don't work in a way that's common among other languages) doesn't make Tcl a toy language, just an odd-man-out. Would you prefer APL comments? But yes, I definitely agree that this is something that needs to be addressed. There are many places I've wanted to put comments but can't, e.g., embedded in a list. One example of such a list is the second argument to [switch], which would be the list of match patterns and scripts. I can put the comment in the script part, but not alongside the match pattern. It's confusing until you learn that the Dodekalogue says what it means and means what it says, despite any (sometimes deceptive) similarities to other languages.
Okay, back to comments in the brace matcher. I've found that calling something "simple" isn't sufficient to describe it. Tcl is said to be simple. Because of criticisms such as yours, I've even said that Tcl is too simple to understand. Tcl's simplicity is in its design, but (except to those who really "get it") this translates to complexity in practice. I have no trouble using it, but I've seen many folks struggle. Why can't I put comments there? / Because that's not where a command would go. Or: Why don't the braces match up right? / Because they don't--- see that brace right there, the one with a pound sign right in front of it? / I thought that was a comment. / Read your Dodekalogue, the brace matcher doesn't care. Seriously, making the brace matcher recognize comments actually was quite difficult to hammer out and explain (only sounds simple in summary, the trick is figuring out what constitutes a comment without having to actually execute it), so I definitely can see why it wasn't done as part of the original design. It sounds like I'm saying a system can either be simple for the implementer or for the user, but never really both. I don't know if that's actually true, but this case is certainly evidence of such.
AMG, update: Here, let me throw a little more fuel on the fire. I know to avoid mismatched unbackslashed braces in comments, but I still get surprised sometimes by mismatched unbackslashed braces in double quotes. The latter can easily happen in code generators. For instance, let's say that a Tcl script is generating some C code. It always emits a certain code snippet, but sometimes it sometimes wraps it inside a for loop. Well, that would consist of the following code, right?
if {$for} {
emit "for (i = 0; i < $limit; ++i) {"
}
emit $code
if {$for} {
emit "}"
}Well, what does Tcl actually do with this code? The second argument to if runs all the way from the opening brace at the end of the first line to the closing brace at the very last line. The [emit $code] line only executes if $for is true. And that's only if there happens to be a command called "}", since the single "}" on the line above the [emit $code] is interpreted as a command name.
The fix is simple: put backslashes in front of the braces inside quotes. But still it surprises me.
This is another case my proposal handles, but it was by no means easy. Not only does the brace matcher have to figure out what constitutes a comment, but it also has to get quoted strings. The rule for a comment isn't simple: it can only start where a command can start; and the rule for quoted strings is only slightly easier: it can only start at a word start.
Cloverfield - Parser shows a years-old and incomplete attempt I made at solving these issues.
TclinaPickleThe response merely emphasizes the original contention. Perhaps it would be helpful to define what is meant by "toy language"
"Tcl is a toy language" doesn't mean it's not expressive, or not a practical means of getting certain things done. It is both of these things. No bones there.
"Tcl is a toy language" really means that its philosophical underpinnings are unsound - it makes design decisions that are easy for the implementer, not the user. In my original rant, I pointed out that I don't want to have certain behaviour rationalized; I want it fixed. Simplicity in a language can be a very good thing, but the problem here is that Tcl's implementation is simple, and such decisions have very unfortunate implications to the user without tangible benefit. Lisp is conceptually even simpler - it is mathematically elegant and reasonably correct. Implementations, though, are not.
If you're not aware of it, there's a famous article, Worse Is Better , on some of the ideas you raised. Well worth a read.