On 10/1/06, Yitzchak Gale
Conor McBride wrote:
Claus Reinke wrote:
...the results of the translation are rather more awkward but -and this is the important point- pattern guards do not add new functionality.
Well, neither do Boolean guards nor even basic pattern matching... one simply should not need to clutter a program with do, return, mplus and fromJust (ugh!), spelling out the semantics of pattern matching in minute detail. For at least 36 years, we've been able to hide all that junk behind a highly readable equational notation. This is one monad we don't need to see.
Some complex things are happening: selections and bindings are happening at the same time. The monad spells it out clearly and concisely, without adding very much weight at all.
I would argue that most Haskell programmers would *never* write the various snippets of code demonstrated in this thread in your way, on the other hand pattern guards are convenient and easy enough to understand (i.e. you don't have to know very much about monads), and probably would get used. I certainly use them (and I *do* understand monads enough to switch to your style of coding if I wanted to)! Your way is nice and elegant if you happen to know enough to understand it, pattern guards are nice and elegant to people who don't.
There has to be a really, really compelling reason to add new syntax to a language. Every bit of new syntax makes a language harder to learn, and less usable for the general user.
I disagree. Adding syntactic sugar is cheap, as long as the core concepts are small and elegant. I believe Haskell has taken this approach so far (or do you want to get rid of e.g. list comprehensions as well? They too are expressible quite elegantly with monads.), and I think pattern guards are an excellent candidate in line with this. It's a "natural" (in terms of "feel", fuzzy I know) generalisation of guards, and simply won't affect anyone who think they are difficult in any way. They are and intuitive and nice. They don't change the behaviour of the "core" language, all they do is add a tiny bit of syntactic sugar to make programmer's lives a little bit easier - and they're not even adding anything completely new, just extending existing features. /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862