Re: [Haskell-cafe] Records (was Re: [Haskell] Improvements to GHC)

On 11/17/05, Cale Gibbard wrote:

On 17/11/05, Sebastian Sylvan wrote:

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On 11/17/05, Greg Woodhouse wrote:

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Isn't there a potential for confusion with function composition (f . g)?

That being said, I like this idea (I just need to think it through a bit).

I've been wanting this for ages. It's SO much better than the current horribly broken records we have. There could be confusion with function composition, but there's no ambiguity (compositon have spaces around the dot, while record accessors do not). Personally I think that the dot is way to good of a symbol to be "wasted" on function composition. I mean, how often do you really use function composition in a way which doesn't obfuscate your code? I use ($) way more often than (.). Some people do use it more often than I do, but I find that in most cases except simple "pipelined" functions it only makes the code harder to read. I'd rather function composition was left out of the prelude alltogether (or defined as (#) or something).

Anyway. The current records system is a wart.

Actually, I didn't mention this in the other post, but why not the other way around? Make record selection (#) or (!) (though the latter gets in the way of array access), and leave (.) for function composition. Personally, I'd like something which looked like an arrow for record selection, but most of the good 2-character ones are unavailable. (~>) is a bit hard to type and looks wrong in some fonts. There's a "triangle" which is not taken, and isn't so hard to type (|>).

I never really understood the attachment to (.) for record selection. There's no reason that we have to make things look like Java and C.

This is going to be highly fuzzy and completely subjective. Here it goes. I find that for selections (records, or qualified modules etc.) I want the operator to be small and so that the important "word groups" become the module or the record. When I read the following two variants myPoint#x myPoint.x I definatly prefer the latter. In the first one the operator is so large that it makes "myPoint" and "x" blend together as you read it (step away from the monitor and squint and you'll see what I mean), whereas in the second example the operator is small and makes the two operands naturally separate slightly when reading it, which makes it easier to tell which identifier is accessed. Also, it's certainly not a BAD thing if Haskell uses the same operators as other languages. With function composition, though, the operator is just as important to identify when reading as the operands are. So I don't think a "big" operator is a problem there - likewise I have no problems with ($) being "large". How about (¤)? It looks like a ring to me, I'm not sure where that's located on a EN keyboard, but it's not terribly inconvenient on my SE keyboard. f ¤ g looks better than "f . g" for function composition, if you ask me. That's my subjective view on why the dot-operator is so darn nice, anyway. Oh and to answer to your other post. I realise that function composition is a fundamental operation, but it's so fundamental that it's quite useless for most real-world cases unless your willing to seriously ubfuscate your code. IMO it really only works well for simple "chains" like "foo . bar . oof . rab" but as soon as you start working with functions that take more parameters it starts looking very unreadable and you'd be better off to just use $ or write out paranthesis and apply arguments explicitly, or better yet, introduce some temporary descriptive variables in a let or where clause. It's a matter of personal preference, but I certainly haven't found it used enough to warrant giving it perhaps the best symbol on the keyboard. /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862