Re: [Haskell-cafe] Wikipedia on first-class object
On Fri, 2007-12-28 at 17:54 -0600, Jonathan Cast wrote: Programming languages are generally classified into three groups, imperative, functional, and logical. The difference is in the style of programming encouraged (or mandated, for older languages) by the language. Usually the divide is imperative v. declarative with the four major paradigms (procedural, OO and logic, FP respectively) being subgroups of those divisions. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 6 Jan 2008, at 3:02 AM, Derek Elkins wrote: On Fri, 2007-12-28 at 17:54 -0600, Jonathan Cast wrote: Programming languages are generally classified into three groups, imperative, functional, and logical. The difference is in the style of programming encouraged (or mandated, for older languages) by the language. Usually the divide is imperative v. declarative with the four major paradigms (procedural, OO and logic, FP respectively) being subgroups of those divisions. And your explanation of this classification is? I find the term `declarative' to be almost completely meaningless. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Sun, 2008-01-06 at 09:45 -0800, Jonathan Cast wrote: On 6 Jan 2008, at 3:02 AM, Derek Elkins wrote: On Fri, 2007-12-28 at 17:54 -0600, Jonathan Cast wrote: Programming languages are generally classified into three groups, imperative, functional, and logical. The difference is in the style of programming encouraged (or mandated, for older languages) by the language. Usually the divide is imperative v. declarative with the four major paradigms (procedural, OO and logic, FP respectively) being subgroups of those divisions. And your explanation of this classification is? I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Many people find any, perhaps all, of the terms: functional, object oriented, imperative to be almost completely meaningless. Mostly the terms have no prescriptive meaning, but rather are defined by example. At any rate, I wasn't and didn't explain anything as that was not my intention. I was merely pointing out that your usage is against the norms and in a way similar in its disconcertingness to saying, American politics is classified into three groups, conservatives, Democrats and libertarians. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Derek Elkins writes: Jonathan Cast wrote: I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Clear, no. Accepted, yes. Let Jonathan Cast repeat that statement to people who organise conferences on Declarative Programming, or those who assembled: http://en.wikipedia.org/wiki/Declarative_programming http://burks.brighton.ac.uk/burks/foldoc/90/29.htm (or http://foldoc.org/foldoc.cgi?declarative+language) I can't see what is the purpose of all your argument... Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Sun, 2008-01-06 at 22:31 +0100, [EMAIL PROTECTED] wrote: Derek Elkins writes: Jonathan Cast wrote: I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Clear, no. Accepted, yes. That was a conjunction: clear AND accepted. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 6 Jan 2008, at 1:31 PM, [EMAIL PROTECTED] wrote: Derek Elkins writes: Jonathan Cast wrote: I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Clear, no. Accepted, yes. Let Jonathan Cast repeat that statement to people who organise conferences on Declarative Programming, or those who assembled: http://en.wikipedia.org/wiki/Declarative_programming http://burks.brighton.ac.uk/burks/foldoc/90/29.htm (or http://foldoc.org/foldoc.cgi?declarative+language) To quote your last citation: declarative language: Any relational language or functional language. Yes, the term `declarative' means something in the sense that we can tell whether any given language is declarative or not, so I should have been more clear. To wit, I do not believe the term `declarative' has any single referent, even in the sense that the term `functional' has any single referent. I find the only similarity between Haskell and Prolog to be that neither is imperative. I can't see what is the purpose of all your argument... Granted. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 6 Jan 2008, at 12:13 PM, Derek Elkins wrote: On Sun, 2008-01-06 at 09:45 -0800, Jonathan Cast wrote: On 6 Jan 2008, at 3:02 AM, Derek Elkins wrote: On Fri, 2007-12-28 at 17:54 -0600, Jonathan Cast wrote: Programming languages are generally classified into three groups, imperative, functional, and logical. NB: I will stipulate that most people consider imperative vs. declarative to be a further hierarchy above this division. I will even stipulate that most people consider the procedural vs. OO distinction other than a distraction :) So I should have said: programming languages may be classified into three groups, ... --- where the groups themselves are generally agreed to exist, to be mutually exclusive, and to capture the vast majority of programming languages. The difference is in the style of programming encouraged (or mandated, for older languages) by the language. Usually the divide is imperative v. declarative with the four major paradigms (procedural, OO and logic, FP respectively) being subgroups of those divisions. And your explanation of this classification is? I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Many people find any, perhaps all, of the terms: functional, object oriented, imperative to be almost completely meaningless. Mostly the terms have no prescriptive meaning, but rather are defined by example. I was trying to work within this framework. Most languages support both imperative and functional paradigms, these days; but there are patterns which are awkward in some languages and natural in others. That is what I consider the main distinction. But, while there are patterns that are natural in all (at least structured) imperative languages and no or few non-imperative ones (like while loops), I don't know of any patterns that are natural in all declarative languages. At any rate, I wasn't and didn't explain anything as that was not my intention. I was merely pointing out that your usage is against the norms As a statistical statement, this may be true. and in a way similar in its disconcertingness to saying, American politics is classified into three groups, conservatives, Democrats and libertarians. Or like saying American politics is classified into three groups, statists, Rothbardians, and Randians :) jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Sun, 2008-01-06 at 13:48 -0800, Jonathan Cast wrote: On 6 Jan 2008, at 1:31 PM, [EMAIL PROTECTED] wrote: Derek Elkins writes: Jonathan Cast wrote: I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Clear, no. Accepted, yes. Let Jonathan Cast repeat that statement to people who organise conferences on Declarative Programming, or those who assembled: http://en.wikipedia.org/wiki/Declarative_programming http://burks.brighton.ac.uk/burks/foldoc/90/29.htm (or http://foldoc.org/foldoc.cgi?declarative+language) To quote your last citation: declarative language: Any relational language or functional language. Yes, the term `declarative' means something in the sense that we can tell whether any given language is declarative or not, so I should have been more clear. To wit, I do not believe the term `declarative' has any single referent, even in the sense that the term `functional' has any single referent. I find the only similarity between Haskell and Prolog to be that neither is imperative. Indeed, you've discovered it. The definition of declarative is often not imperative. (Or vice versa, where, as I said earlier, these are primarily defined by example rather than some predicate.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Derek Elkins writes: Jonathan Cast wrote: I find the only similarity between Haskell and Prolog to be that neither is imperative. Indeed, you've discovered it. The definition of declarative is often not imperative. I disagree. Practically. (I won't discuss doctrinal matter nor linguistic hairsplitting). The relational syntax of Prolog is more universal than the functional notation, since you have logic variables and logical-non-determinism, and - thus - the possibility of making predicates where the roles of input and output parameters are not pre-assigned, - - but there is a *strong* (meaning important) functional layer within, and plenty of Prolog algorithms are expressed similarly in Lisp or in Haskell. Many non-deterministic ones have natural translation into the List monad. Some circular definitions using laziness are related to ones with non-instantiated logical variables. If you don't want to see similarities, you won't. But I assure you that I have profited enormously from tha *affinities* between functional and logic approaches, and you won't convince me that declarative is without substance. Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Wikipedia on first-class object
Jerzy wrote: The relational syntax of Prolog is more universal than the functional notation, since you have logic variables and logical-non-determinism, and Isn't this just because mathematically, a function *is* a relation, but not vice versa? A relation being just a subset of a Cartesian product of sets, while a function being a special kind of relation for which each element in the domain has exactly one image? So relations are inherently much more universal than functions, but they are not that practical to work with (for a computer and/or human?). Gee, I should not talk about math here, as you category theory guys know a thousand times more math than I do ;-) Cheers, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Peter Verswyvelen writes: Jerzy wrote: The relational syntax of Prolog is more universal than the functional notation, since you have logic variables and logical-non-determinism, and Isn't this just because mathematically, a function *is* a relation, but not vice versa? A relation being just a subset of a Cartesian product of sets, while a function being a special kind of relation for which each element in the domain has exactly one image? So relations are inherently much more universal than functions, but they are not that practical to work with (for a computer and/or human?). You are right. Yes, functions are subsets of relations, and the affinity between logical and functional programming is all but accidental. But relations ARE PRACTICAL! Prolog, Mercury, etc. use them. Leda, Life ... Combined paradigms are not so exotic. Gee, I should not talk about math here, as you category theory guys know a thousand times more math than I do ;-) On the contrary, you should. Tell what is interesting for you. Don't let hairsplitters monopolize the discussion of mathematical side of Haskell. I am sick seeing that 75% of true deep discussion turns around ... sorry for the swearword - ... bottom. Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Sun, 2008-01-06 at 23:28 +0100, [EMAIL PROTECTED] wrote: Derek Elkins writes: Jonathan Cast wrote: I find the only similarity between Haskell and Prolog to be that neither is imperative. Indeed, you've discovered it. The definition of declarative is often not imperative. I disagree. Practically. (I won't discuss doctrinal matter nor linguistic hairsplitting). I wasn't being that serious there, though oftentimes declarative -is- used in a way that is mostly meaningless or as a buzzword. One thing I will stand by, however, is that the consensus is that declarative and imperative are meant to be exhaustive and ideally disjoint (though where to draw the line is tricky), and thus in that sense, declarative is not imperative (and, as I said originally though you elided it, vice versa.) The relational syntax of Prolog is more universal than the functional notation, since you have logic variables and logical-non-determinism, and - thus - the possibility of making predicates where the roles of input and output parameters are not pre-assigned, - - but there is a *strong* (meaning important) functional layer within, and plenty of Prolog algorithms are expressed similarly in Lisp or in Haskell. Many non-deterministic ones have natural translation into the List monad. Some circular definitions using laziness are related to ones with non-instantiated logical variables. If you don't want to see similarities, you won't. But I assure you that I have profited enormously from tha *affinities* between functional and logic approaches, and you won't convince me that declarative is without substance. declarative is often used in a way where HTML, XML and such are declarative languages. At any rate, also in the elided part of my reply, was the statement that imperative/declarative are often defined by example, and the above is just such a case (unless you have a clear definition of functional and logical). This simply defines declarative to mean functional+logical making declarative a pure name devoid of any descriptive power. To make this email constructive, however, I will propose a slightly less fuzzy criterion: namely a declarative language is one that, via the Curry-Howard correspondence(s), corresponds strongly with (a relatively standard) logic. This arguably can be used to give some oomph to the usage of the term declarative rather than it being just a name, though I'll not bother. This recovers the fact that functional and logic languages are declarative and gives a -specific- similarity. It agrees fairly well with the ordering more declarative than determined by consensus. Finally, it points the way to allowing other languages rather than not (functional or logical) = not declarative. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Am Freitag, 28. Dezember 2007 07:49 schrieben Sie: On Thu, 27 Dec 2007 18:19:47 +0200, Wolfgang Jeltsch [EMAIL PROTECTED] wrote: Am Donnerstag, 27. Dezember 2007 16:34 schrieb Cristian Baboi: I'll have to trust you, because I cannot test it. let x=(1:x); y=(1:y) in x==y . I also cannot test this: let x=(1:x); y=1:1:y in x==y In these examples, x and y denote the same value but the result of x == y is _|_ (undefined) in both cases. So (==) is not really equality in Haskell but a kind of weak equality: If x doesn’t equal y, x == y is False, but if x equals y, x == y might be True or undefined. Thank you. I can only notice that y always has an even number of 1, which is not the case for x :-) Both have an infinite number of 1. Why do you say “always”? It seems that you think of x and y as “variables” whose values change over time. This is not the case. They both have a single value for all time: the infinite list consisting only of 1. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Am Freitag, 28. Dezember 2007 07:49 schrieben Sie: On Thu, 27 Dec 2007 18:14:53 +0200, Wolfgang Jeltsch [EMAIL PROTECTED] wrote: Am Donnerstag, 27. Dezember 2007 15:53 schrieb Cristian Baboi: On Thu, 27 Dec 2007 16:50:10 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Absolutly. Every expression in Haskell denotes a value. Now, we've not agreed what value means, but to me it is a value. :) It is one value, or several ? It is one value with parts that are values themselves. It is one value or a SET of values ? What are the parts ? A set of values is again a value. So is a list of values. This is similar to C++ where a field of an object can again be an object. [1..] is a value of type [Int] and every element can be considered a part of this value. Best wishes, Wolfgang P.S.: Didn’t send this to the list in the first place. I don’t like mailing lists which don’t set the Reply-To: field. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Am Freitag, 28. Dezember 2007 08:12 schrieb Cristian Baboi: On Thu, 27 Dec 2007 17:35:54 +0200, Jonathan Cast [EMAIL PROTECTED] wrote: Only on Von Neuman machines. Haskell implementations are not required to run on Von Neuman machines. That's why the language is called functional. (Imperative languages, by contrast, are just abstractions of the underlying Von Neuman architecture, which is probably the source of your confusion). Can you tell me what is it that make a language imperative ? When I learned about formal grammars and languages, there was no discussion about this. This is because a formal language (set of words) only consideres the syntactic aspect and formal grammars are only about describing formal languages. In contrast, imperative vs. declarative is about semantics. A language is imperative if programs written in this language say how something should be done instead of what should be the outcome. This description is rather informal, of course. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Cristian Baboi wrote: http://en.wikipedia.org/wiki/First-class_object I'll guess that 5,9,12 does not apply to Haskell functions. I think there is a basic semantic difference between what the author of that article meant by the word function and what we mean by that word when we are talking about Haskell. In the article, function means a concrete data object that specifies how to compute something. In Haskell, a function is closer to the mathematical idea of a function. Functions specify relationships between elements of certain types, and then the compiler uses them to create code to do your computation. But there is no obligation for a compiler to create any concrete data structure that corresponds to a function. Often it does in practice, but not always. On the other hand, functions are members of types that are just like any other Haskell type. They are first-class in that sense. Like any type, only certain operations make sense on functions. Strings can be compared to each other for equality and written to a disk, and you can take the logarithm of a float, but none of those operations make sense for functions. In particular, two functions are equal only if they produce the same value for every input, and in general it is impossible for a computer to check that. -Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 12/27/07, Cristian Baboi [EMAIL PROTECTED] wrote: http://en.wikipedia.org/wiki/First-class_object The term was coined by Christopher Strachey in the context of functions as first-class citizens in the mid-1960's.[1] Depending on the language, this can imply: 1. being expressible as an anonymous literal value 2. being storable in variables 3. being storable in data structures 4. having an intrinsic identity (independent of any given name) 5. being comparable for equality with other entities 6. being passable as a parameter to a procedure/function 7. being returnable as the result of a procedure/function 8. being constructable at runtime 9. being printable 10. being readable 11. being transmissible among distributed processes 12. being storable outside running processes I'll guess that 5,9,12 does not apply to Haskell functions. I don't think this is meant as a list of requirements, but as examples of what being first class *can* mean. So yes, in Haskell some of these points don't make much sense. -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Fwd: Re: [Haskell-cafe] Wikipedia on first-class object
--- Forwarded message --- From: Cristian Baboi [EMAIL PROTECTED] To: Yitzchak Gale [EMAIL PROTECTED] Cc: Subject: Re: [Haskell-cafe] Wikipedia on first-class object Date: Thu, 27 Dec 2007 12:21:44 +0200 I think I found the answer to why functions cannot be written to files. This is by design. Haskell must be free. Enabling writing functions to files, might make it ilegal in some countries. :-) On Thu, 27 Dec 2007 11:10:21 +0200, Yitzchak Gale [EMAIL PROTECTED] wrote: Like any type, only certain operations make sense on functions. Strings can be compared to each other for equality and written to a disk, and you can take the logarithm of a float, but none of those operations make sense for functions. In particular, two functions are equal only if they produce the same value for every input, and in general it is impossible for a computer to check that. -Yitz Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re: [Haskell-cafe] Wikipedia on first-class object
Cristian Baboi wrote: I think I found the answer to why functions cannot be written to files. This is by design. Haskell must be free. Enabling writing functions to files, might make it ilegal in some countries. :-) Ha, excellent! I imagine that is what Haskell must have been like before they invented the IO monad. It certainly was safer then. -Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Thinking about files and types, I recalled that in Pascal files must have types. On Thu, 27 Dec 2007 12:40:22 +0200, Yitzchak Gale [EMAIL PROTECTED] wrote: I'm not sure that in Haskell one can say that storing a value of some type to disk is an operation defined on that type. It is. For example: hPutStr :: Handle - String - IO () The result type of this function is IO (), which means an IO action. In this case, the semantics of the action are that, when performed, it writes the bytes into a file. Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Cristian Baboi wrote: Ah! You must have been thinking that function in Haskell are members of DATA types. Or, to put it another way, Haskell make no distinction between data types and function types. Yes. I wrote: Like any type, only certain operations make sense on functions... Yes, but one can store the result of an operation to disk except in the particular case the result happen to be a function. No, you can only store the result of an operation to disk in the particular case that the result type represents a list of bytes. Otherwise, you have to serialize it first... But it is not clear at all how you could define a general serialization method for functions. Isn't that confusing levels of abstractions ? Of course functions are bytes, 'cause they are already stored as bytes in RAM. That is just the point. A function in Haskell is an abstraction, not bytes in RAM. The compiler might implement the same function in several places, with different bytes in each place. Or it might decide to combine it into other functions, and not store any bytes in RAM at all for this function. The function itself represents a way of doing a calculation. It is not an object that can do the calculation. I'm not sure that in Haskell one can say that storing a value of some type to disk is an operation defined on that type. It is. For example: hPutStr :: Handle - String - IO () And this is a property of the type String ? The function hPutStr appears in the definition of the type String ? Ah, you are thinking of operation on a type in the OOP sense. Sorry, I wasn't clear. When I said only certain operations make sense on each type, I just meant that there are only certain things you can do with the type. In Haskell, the things you can do with a type are the functions you can define that mention that type in their signature. -Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Thu, 27 Dec 2007 14:37:51 +0200, Yitzchak Gale [EMAIL PROTECTED] wrote: I wrote: Like any type, only certain operations make sense on functions... Yes, but one can store the result of an operation to disk except in the particular case the result happen to be a function. No, you can only store the result of an operation to disk in the particular case that the result type represents a list of bytes. Otherwise, you have to serialize it first... But it is not clear at all how you could define a general serialization method for functions. Isn't that confusing levels of abstractions ? Of course functions are bytes, 'cause they are already stored as bytes in RAM. That is just the point. A function in Haskell is an abstraction, not bytes in RAM. The compiler might implement the same function in several places, with different bytes in each place. Or it might decide to combine it into other functions, and not store any bytes in RAM at all for this function. The function itself represents a way of doing a calculation. It is not an object that can do the calculation. I think you try to say that the time cannot be stored. Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Thu, 27 Dec 2007 14:37:51 +0200, Yitzchak Gale [EMAIL PROTECTED] wrote: I wrote: Like any type, only certain operations make sense on functions... Yes, but one can store the result of an operation to disk except in the particular case the result happen to be a function. No, you can only store the result of an operation to disk in the particular case that the result type represents a list of bytes. Otherwise, you have to serialize it first... But it is not clear at all how you could define a general serialization method for functions. Isn't that confusing levels of abstractions ? Of course functions are bytes, 'cause they are already stored as bytes in RAM. That is just the point. A function in Haskell is an abstraction, not bytes in RAM. The compiler might IMPLEMENT the same function in several places, with different bytes in each place. Or it might decide to combine it into other functions, and not store any bytes in RAM at all for this function. See ? The function itself represents a way of doing a calculation. It is not an object that can do the calculation. Then trees of functions are ... I'm not sure that in Haskell one can say that storing a value of some type to disk is an operation defined on that type. It is. For example: hPutStr :: Handle - String - IO () And this is a property of the type String ? The function hPutStr appears in the definition of the type String ? Ah, you are thinking of operation on a type in the OOP sense. Sorry, I wasn't clear. When I said only certain operations make sense on each type, I just meant that there are only certain things you can do with the type. In Haskell, the things you can do with a type are the functions you can define that mention that type in their signature. How can one define in the language STORAGE of things ? Storage of numbers for example ? You said that the TYPE of a function forbids me somehow to store it in a file. Now I understand that not the type forbids me, but the lack of a function with apropriate types. Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Thu, 27 Dec 2007 14:02:36 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Comparing functions is certainly possible in Haskell, but there's no standard function that does it. If course, it might not terminate, but the same is true for many other comparable objects in Haskell, e.g., infinite lists (which are isomorphic to Nat-T). The list [1 .. ] is a single value in Haskell ? Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Fwd: Re: [Haskell-cafe] Wikipedia on first-class object
How about x below: let x=(1:x) in x ? Is x a single value in Haskell ? --- Forwarded message --- From: Cristian Baboi [EMAIL PROTECTED] To: Lennart Augustsson [EMAIL PROTECTED] Cc: haskell-cafe@haskell.org haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] Wikipedia on first-class object Date: Thu, 27 Dec 2007 16:08:58 +0200 On Thu, 27 Dec 2007 14:02:36 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Comparing functions is certainly possible in Haskell, but there's no standard function that does it. If course, it might not terminate, but the same is true for many other comparable objects in Haskell, e.g., infinite lists (which are isomorphic to Nat-T). The list [1 .. ] is a single value in Haskell ? Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re: [Haskell-cafe] Wikipedia on first-class object
Absolutly. Every expression in Haskell denotes a value. Now, we've not agreed what value means, but to me it is a value. :) -- Lennart On Dec 27, 2007 3:28 PM, Cristian Baboi [EMAIL PROTECTED] wrote: How about x below: let x=(1:x) in x ? Is x a single value in Haskell ? --- Forwarded message --- From: Cristian Baboi [EMAIL PROTECTED] To: Lennart Augustsson [EMAIL PROTECTED] Cc: haskell-cafe@haskell.org haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] Wikipedia on first-class object Date: Thu, 27 Dec 2007 16:08:58 +0200 On Thu, 27 Dec 2007 14:02:36 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Comparing functions is certainly possible in Haskell, but there's no standard function that does it. If course, it might not terminate, but the same is true for many other comparable objects in Haskell, e.g., infinite lists (which are isomorphic to Nat-T). The list [1 .. ] is a single value in Haskell ? Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 27 Dec 2007, at 4:57 AM, Cristian Baboi wrote: On Thu, 27 Dec 2007 12:40:22 +0200, Yitzchak Gale [EMAIL PROTECTED] wrote: I wrote: On the other hand, functions are members of types that are just like any other Haskell type. They are first-class in that sense. Cristian Baboi wrote: I guess that would apply to any typed language. Perhaps. But for many typed languages, it is not practical to use. There may be problems with type safety, or it may create a program that would be considered hard to understand. For example, in Haskell, you create a list of functions just the same way you create a list of anything else. You can then map a value across the functions, or fold the functions together with the composition operator, etc. These are normal, clear idioms in Haskell that could easily appear in any simple program. That is also true for some other functional programming languages, but it is rare for imperative ones. Sometimes there is a particular style within a language that works something like this. For example, you can use C++ with STL that way in a certain sense. Anyway, that is what I think it means when we say that functions are first-class in Haskell. Ah! You must have been thinking that function in Haskell are members of DATA types. Or, to put it another way, Haskell make no distinction between data types and function types. Like any type, only certain operations make sense on functions. Strings can be compared to each other for equality and written to a disk, and you can take the logarithm of a float, but none of those operations make sense for functions. In particular, two functions are equal only if they produce the same value for every input, and in general it is impossible for a computer to check that. Yes, but one can store the result of an operation to disk except in the particular case the result happen to be a function. No, you can only store the result of an operation to disk in the particular case that the result type represents a list of bytes. Otherwise, you have to serialize it first. Happily, Haskell has some cool tools for easily creating serialization methods. And there are a number methods that are already provided in the libraries for many types and for many uses - the Read and Show classes are just one example. But it is not clear at all how you could define a general serialization method for functions. If you can come up with one, please post it to Hackage. :) Isn't that confusing levels of abstractions ? Of course functions are bytes, 'cause they are already stored as bytes in RAM. Only on Von Neuman machines. Haskell implementations are not required to run on Von Neuman machines. That's why the language is called functional. (Imperative languages, by contrast, are just abstractions of the underlying Von Neuman architecture, which is probably the source of your confusion). jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re: [Haskell-cafe] Wikipedia on first-class object
On Thu, 27 Dec 2007 16:50:10 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Absolutly. Every expression in Haskell denotes a value. Now, we've not agreed what value means, but to me it is a value. :) It is one value, or several ? Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re: [Haskell-cafe] Wikipedia on first-class object
One value. One infinite value. On Dec 27, 2007 3:53 PM, Cristian Baboi [EMAIL PROTECTED] wrote: On Thu, 27 Dec 2007 16:50:10 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Absolutly. Every expression in Haskell denotes a value. Now, we've not agreed what value means, but to me it is a value. :) It is one value, or several ? Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Am Donnerstag, 27. Dezember 2007 16:34 schrieb Cristian Baboi: I'll have to trust you, because I cannot test it. let x=(1:x); y=(1:y) in x==y . I also cannot test this: let x=(1:x); y=1:1:y in x==y In these examples, x and y denote the same value but the result of x == y is _|_ (undefined) in both cases. So (==) is not really equality in Haskell but a kind of weak equality: If x doesn’t equal y, x == y is False, but if x equals y, x == y might be True or undefined. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re: [Haskell-cafe] Wikipedia on first-class object
I'll have to trust you, because I cannot test it. let x=(1:x); y=(1:y) in x==y . I also cannot test this: let x=(1:x); y=1:1:y in x==y On Thu, 27 Dec 2007 17:29:12 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: One value. One infinite value. On Dec 27, 2007 3:53 PM, Cristian Baboi [EMAIL PROTECTED] wrote: On Thu, 27 Dec 2007 16:50:10 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Absolutly. Every expression in Haskell denotes a value. Now, we've not agreed what value means, but to me it is a value. :) It is one value, or several ? Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK part001.htm - is OK http://www.eset.com Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 27 Dec 2007, at 8:53 AM, Cristian Baboi wrote: On Thu, 27 Dec 2007 16:50:10 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Absolutly. Every expression in Haskell denotes a value. Now, we've not agreed what value means, but to me it is a value. :) It is one value, or several ? It is one and the same value, now and for ever, and in every incarnation on every Haskell machine. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 27 Dec 2007, at 8:08 AM, Cristian Baboi wrote: On Thu, 27 Dec 2007 14:02:36 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Comparing functions is certainly possible in Haskell, but there's no standard function that does it. If course, it might not terminate, but the same is true for many other comparable objects in Haskell, e.g., infinite lists (which are isomorphic to Nat-T). The list [1 .. ] is a single value in Haskell ? Yes. Of course. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 27 Dec 2007, at 8:28 AM, Cristian Baboi wrote: How about x below: let x=(1:x) in x ? Is x a single value in Haskell ? (let x=1:x in x) is. x went out of scope a couple of lines back. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 27 Dec 2007, at 9:34 AM, Cristian Baboi wrote: I'll have to trust you, because I cannot test it. let x=(1:x); y=(1:y) in x==y . I also cannot test this: let x=(1:x); y=1:1:y in x==y Correct. You could try proving it. Or you could try proving that these expressions are equal to _|_. Equality is defined on lists because we frequently use finite lists, where it makes sense. Infinite lists are more like functions --- useful in the intermediate stages of computation, but really orthogonal to everything you think you know about computing. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Am Donnerstag, 27. Dezember 2007 16:57 schrieb Cristian Baboi: On Thu, 27 Dec 2007 17:52:19 +0200, Jonathan Cast Which is why Haskell treats IO as a domain specific language. Good to know. I intended to use Haskell for algorithms, but it seems it is not so good at them. Why is I/O needed for algorithms? And the fact that I/O is embedded into Haskell as a kind of a domain specific language doesn’t mean that Haskell is bad at I/O. As Simon Peyton Jones put it: Haskell is the world’s finest imperative programming language. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Am Donnerstag, 27. Dezember 2007 15:53 schrieb Cristian Baboi: On Thu, 27 Dec 2007 16:50:10 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Absolutly. Every expression in Haskell denotes a value. Now, we've not agreed what value means, but to me it is a value. :) It is one value, or several ? It is one value with parts that are values themselves. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Bulat Ziganshin wrote: here T is any type. you said that values of ANY TYPE can be saved to disk, so show us the way ... try to prove that this mean that value of ANY type may be saved to disk Run another program that uses lots of memory, and watch the entire Haskell program's memory be swapped out to disk. Better yet, suspend-to-disk (or hibernate) your computer. Voila -- values of any and all types have been saved to disk! In a limited fashion, of course. Isaac ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Thu, 27 Dec 2007 18:13:57 +0200, Wolfgang Jeltsch [EMAIL PROTECTED] wrote: Am Donnerstag, 27. Dezember 2007 16:57 schrieb Cristian Baboi: On Thu, 27 Dec 2007 17:52:19 +0200, Jonathan Cast Which is why Haskell treats IO as a domain specific language. Good to know. I intended to use Haskell for algorithms, but it seems it is not so good at them. Why is I/O needed for algorithms? And the fact that I/O is embedded into Haskell as a kind of a domain specific language doesn’t mean that Haskell is bad at I/O. As Simon Peyton Jones put it: Haskell is the world’s finest imperative programming language. An algorithm is a finite recipe that allow one to solve a class of problems in a mechanical way. To be able to use the algorithm one must be able to read it. To be able to communicate the algorithm, one must be able to write it. When I mentioned that IO is not needed for pebbles, I was joking. Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Thu, 27 Dec 2007 18:14:53 +0200, Wolfgang Jeltsch [EMAIL PROTECTED] wrote: Am Donnerstag, 27. Dezember 2007 15:53 schrieb Cristian Baboi: On Thu, 27 Dec 2007 16:50:10 +0200, Lennart Augustsson [EMAIL PROTECTED] wrote: Absolutly. Every expression in Haskell denotes a value. Now, we've not agreed what value means, but to me it is a value. :) It is one value, or several ? It is one value with parts that are values themselves. It is one value or a SET of values ? What are the parts ? Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Thu, 27 Dec 2007 18:19:47 +0200, Wolfgang Jeltsch [EMAIL PROTECTED] wrote: Am Donnerstag, 27. Dezember 2007 16:34 schrieb Cristian Baboi: I'll have to trust you, because I cannot test it. let x=(1:x); y=(1:y) in x==y . I also cannot test this: let x=(1:x); y=1:1:y in x==y In these examples, x and y denote the same value but the result of x == y is _|_ (undefined) in both cases. So (==) is not really equality in Haskell but a kind of weak equality: If x doesn’t equal y, x == y is False, but if x equals y, x == y might be True or undefined. Thank you. I can only notice that y always has an even number of 1, which is not the case for x :-) Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Thu, 27 Dec 2007 17:35:54 +0200, Jonathan Cast [EMAIL PROTECTED] wrote: Only on Von Neuman machines. Haskell implementations are not required to run on Von Neuman machines. That's why the language is called functional. (Imperative languages, by contrast, are just abstractions of the underlying Von Neuman architecture, which is probably the source of your confusion). Can you tell me what is it that make a language imperative ? When I learned about formal grammars and languages, there was no discussion about this. Information from NOD32 This message was checked by NOD32 Antivirus System for Linux Mail Servers. part000.txt - is OK http://www.eset.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
