[Haskell-cafe] Re: Why does Haskell have the if-then-else syntax?
Mike Gunter wrote: I had hoped the History of Haskell paper would answer a question I've pondered for some time: why does Haskell have the if-then-else syntax? The paper doesn't address this. What's the story? For what it's worth, I have been asking myself the same question several times. If/then/else syntax could be replaced by a regular (lazy) function without any noticeable loss. Almost every time I use if/then/else I end up changing it to a case expression on teh underlying data (which is almost never Bool); the only exception being simple one liners, and for those a function would be even more concise. IMHO, the next standardized version of Haskell, however named, should abandon the special if/then/else syntax so we'll have at least /one/ item where the language becomes smaller and simpler. Remember: Perfection is reached not when there is nothing more to add, but rather when there is nothing more to take away. On another note, I remember reading a paper proposing to generalize if/then/else to arbitrary (so-called) dist-fix operators, using something like partial backquoting, as in `if condition `then` true_branch `else` false_branch fi` Can't remember the exact title of the paper, nor the details, but it was something to do with adding macros to Haskell. Cheers, Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why does Haskell have the if-then-else syntax?
G'day all. Quoting Benjamin Franksen [EMAIL PROTECTED]: For what it's worth, I have been asking myself the same question several times. If/then/else syntax could be replaced by a regular (lazy) function without any noticeable loss. I believe that if-then-else cannot be replaced by a regular function for the same reason that regular function application and ($) are not identical. The loss may not be noticeable, but it's still a loss. It could be replaced by a case-switch-on-Bool, though. IMHO, the next standardized version of Haskell, however named, should abandon the special if/then/else syntax so we'll have at least /one/ item where the language becomes smaller and simpler. The de facto Haskell philosophy, if you read the history paper, is to have a small core language with a lot of syntactic sugar. The syntactic sugar is specified by translation to the core language. The small core ensures that Haskell remains simple. If you discount changes in the type system, the Haskell core language is as simple now as it was in 1989. Remember: Perfection is reached not when there is nothing more to add, but rather when there is nothing more to take away. Perfection is asymptotically approached when arbitrary restrictions are removed and special cases are dumped in favour of general, theoretically sound, principles. Perfection will never be reached in a practical programming language, but it may be asymptotically approached. Cheers, Andrew Bromage ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Why does Haskell have the if-then-else syntax?
Confusingly, if c then t else f Also works, although no-one really knows why. Actually, it doesn't work inside a `do' layout, Stefan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Why does Haskell have the if-then-else syntax?
On 7/26/06, Donn Cave [EMAIL PROTECTED] wrote: That looks to me like a different way to spell if then else, but maybe that's the answer to the question - conceptually, for every then there really is an else, however you spell it, and only in a procedural language does it make any sense to leave it implicit. The exception that proves the rule is else return () -, e.g., ... Strictly speaking that generalizes to any functional context where a generic value can be assigned to the else clause, but there don't tend to be that many other such contexts. Does that answer the question? I believe his question was why if-then-else is syntax, rather than the function he gave. Since haskell is non-strict, it doesn't need to be implemented as syntax (unlike, say, scheme, where it needs to be a special form/macro to avoid executing both branches). I imagine the answer is that having the syntax for it looks nicer/is clearer. if a b c could be more cryptic than if a then b else c for some values of a, b and c. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why does Haskell have the if-then-else syntax?
On 7/27/06, Dan Doel [EMAIL PROTECTED] wrote: On 7/26/06, Donn Cave [EMAIL PROTECTED] wrote: That looks to me like a different way to spell if then else, but maybe that's the answer to the question - conceptually, for every then there really is an else, however you spell it, and only in a procedural language does it make any sense to leave it implicit. The exception that proves the rule is else return () -, e.g., ... Strictly speaking that generalizes to any functional context where a generic value can be assigned to the else clause, but there don't tend to be that many other such contexts. Does that answer the question? I believe his question was why if-then-else is syntax, rather than the function he gave. Since haskell is non-strict, it doesn't need to be implemented as syntax (unlike, say, scheme, where it needs to be a special form/macro to avoid executing both branches). I imagine the answer is that having the syntax for it looks nicer/is clearer. if a b c could be more cryptic than if a then b else c for some values of a, b and c. Also, you get less parenthesis: myAbs x = if x 0 then negate x else x /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
