A little F# for you
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Josh Smith wrote:
'head::tail' means "if it exists, remove the first item in the list
Wouldnt that just destructure your input list into 'head' and 'tail' variable? Perhaps the '::' has special meaning? :confused:
xacc.ide
The rule of three: "The first time you notice something that might repeat, don't generalize it. The second time the situation occurs, develop in a similar fashion -- possibly even copy/paste -- but don't generalize yet. On the third time, look to generalize the approach."leppie wrote:
Wouldnt that just destructure your input list into 'head' and 'tail' variable?
When used on the left hand side of a pattern match, yes. When used on the right hand side, it's just a cons operator (i.e. adds an element to the front of a list). So,
blah head::tail -> head::tailleaves the list unchanged. -
Chris Maunder wrote:
That looks like a huge advancement in clarity and code maintainability.
Hahaha. Yeah right. I get the feeling that F# isn't going to become a "mainstream" .NET language anytime soon. It's out there: far, far out there. It has virtues different from clarity and code maintainability. I'm just a newbie so don't quote me, but supposedly using F# as a functional programming language allows you to more easily write code which can be parallelized across multiple processors or cores. I'm interested to see how to do that, because I think that's an important aspect of modern software design.
:josh: My WPF Blog[^] Without a strive for perfection I would be terribly bored.
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Steve Echols wrote:
Whoa!
My sentiments exactly! The hardest part about learning F#, for me, is the fact that it has both new syntax and new concepts (well, new for me anyways). I must say, though, that I haven't had this much geeky fun in a long time! There's nothing better than freeing your mind a little bit, and thinking about things from a totally different perspective. :-D
:josh: My WPF Blog[^] Without a strive for perfection I would be terribly bored.
Josh Smith wrote:
There's nothing better than freeing your mind a little bit,
As long as it does not fall out and get lost in the process :)
Rocky <>< Blog Post: MVC for ASP.NET! Tech Blog Post: Cheap Biofuels and Synthetics coming soon? Tech Sites: SilverlightCity.com ~ TheSilverlightDirectory.com ~ TheWPFDirectory.com
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If it took me almost 7 years to start coding in .net, you can imagine how excited I am about F#...
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
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"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001:laugh:
Rocky <>< Blog Post: MVC for ASP.NET! Tech Blog Post: Cheap Biofuels and Synthetics coming soon? Tech Sites: SilverlightCity.com ~ TheSilverlightDirectory.com ~ TheWPFDirectory.com
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Having studied Miranda for far longer than humanely reasonable, nearly 6 months, the example given just looks like a very syntactically ineffecient list comprehension. List comprehensions are fantastically powerful once you've wrapped your head around how to use them. There is a more fundamental problem here though:- Purely functional and declarative languages set out to tell the computer what result you want but provide no way to specify how the computer is to get the result, or what it should do with it. Purely procedural languages tell the computer exactly what to do but it's very hard for a person to determine from reading one what the expected result might be. Both of these approaches have merit but are only properly leveraged when they are 'pure'. As soon as you mix the concepts together you loose the benefits of both without gaining the advantages of either. The worst aspects of C++ for example are the ones that are partially declarative at run time like, There exists a giblet called thing => giblet thing = new giblet;. These areas are where the opaqueness that causes most problems with learning, correctness and performance come in. As F# appears, like 'managed' C++ to be an attempt to mix these approaches, albeit biased towards the functional I guess it will fail just as spectacularly. What is really needed is a pure functional language that manipulates primitives which themsleves are purely procedural components, a kind of functional COM. stl gets a little way and Boost a little further but both are hamstrung by language limitations. We're not there yet :)
Nothing is exactly what it seems but everything with seems can be unpicked.
Can you reply to any post without at least a few paragraphs that require reading more than once? Are you in anyway related to the Grand Negus?
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If it took me almost 7 years to start coding in .net, you can imagine how excited I am about F#...
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
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"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001 -
Cool - your next task is to learn a) how to apply implicitly recursive functions like
foldandmaprather than explicit recursion, and b) recognise when they can be applied. To use your example, except using Haskell, 'cause that's what I like: Explicit recursion:sum [] = 0 sum (head:tail) = head + (sum tail)Differences from F# - recursion and pattern matching don't need to be explicitly stated. Oh, and if you ask Haskell what the type of
sumis, it'll reply with(Num t) => [t] -> t- basically saying thatsumis now defined for lists of any numeric type...polymorphism at work - uber cool! Implicit recursion:sum = foldl (+) 0A fold combines all elements of a collection using some function - so
sumcombines all elements of a list using the + operator (Haskell lets you use operator as functions if you surround them with brackets) starting with the accumulating value set to zero. Oh - and even though I've not defined any parameters to this sum definition, it does take one -sumis defined as a partial application offoldl, so it's equivalent tosum nums = foldl (+) 0 nums. Oh - and this definition ofsumis defined over all numeric lists as well :-) - the type offoldlis(a -> b -> a) -> a -> [b] -> a-aandbare arbitrary types,(+)has type(Num a) => a -> a -> aand0has type(Num t) => t. Combine those types all together and you get the same as the first definition ofsum! OK - I'm an FP language dweeb, I'll admit it...Well, I read this and I'm still not sure I get it. Aah - wait a second, with my mathematician head on I get it.
Deja View - the feeling that you've seen this post before.
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I've been studying F# a lot recently and find it really mind-bending. Tomas Petricek, a fellow CPian, let me sneak preview his series of F# articles and they are very good. I took one of his examples and modified it a bit. The following code displays "sum = 6", but how that happens is other-worldly...check it out:
#light
let rec sum nums =
match nums with
| head::tail -> head + sum(tail)
| [] -> 0
printf "sum = %i" (sum [1; 2; 3])Weird, eh? F# is coooool. :cool:
:josh: My WPF Blog[^] Without a strive for perfection I would be terribly bored.
Perl made entirely from Regexes and then encrypted in Hex, is still more understandable than that. What's wrong with debug.Print("Sum = 6");
Ninja (the Nerd)
Confused? You will be... -
Well, I read this and I'm still not sure I get it. Aah - wait a second, with my mathematician head on I get it.
Deja View - the feeling that you've seen this post before.
OK - lets do it in C++... Explicit recursion:
template<class ListIter> std::iterator_traits<ListIter>::value_type sum(ListIter begin, ListIter end) { if (begin == end) return 0; // == sum [] = 0 if (begin != end) return (*begin) + sum(begin+1, end); // == sum (head:tail) = head + (sum tail) ... well, kind of }Implicit recursion:
template<class ListIter> std::iterator_traits<ListIter>::value_type sum(ListIter begin, ListIter end) { return std::accumulate(begin, end, 0, std::plus<std::iterator_traits<ListIter>::value_type>()); }We're representing lists using the pair
(ListIter begin, ListIter end)and the set of types for which this compiles is less easy to determine, but that aside it's pretty much the same as the Haskell code, even down to being polymorphic. In C++,std::transform==mapandstd::accumulate==foldl. -
Can you reply to any post without at least a few paragraphs that require reading more than once? Are you in anyway related to the Grand Negus?
Yes.
Nothing is exactly what it seems but everything with seems can be unpicked.
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That looks like a huge advancement in clarity and code maintainability. (Where's the sarcasm icon when I need it)
cheers, Chris Maunder
CodeProject.com : C++ MVP
Really a nice reply!! :laugh: Cheers
You have the thought that modern physics just relay on assumptions, that somehow depends on a smile of a cat, which isn’t there.( Albert Einstein)
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I've been studying F# a lot recently and find it really mind-bending. Tomas Petricek, a fellow CPian, let me sneak preview his series of F# articles and they are very good. I took one of his examples and modified it a bit. The following code displays "sum = 6", but how that happens is other-worldly...check it out:
#light
let rec sum nums =
match nums with
| head::tail -> head + sum(tail)
| [] -> 0
printf "sum = %i" (sum [1; 2; 3])Weird, eh? F# is coooool. :cool:
:josh: My WPF Blog[^] Without a strive for perfection I would be terribly bored.
Superb, just a couple of possible improvements that could be made: 1) Replace all readable characters with further punctuation marks 2) Put a C somewhere in the name of the language and hey presto - mainstream! Rich
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I've been studying F# a lot recently and find it really mind-bending. Tomas Petricek, a fellow CPian, let me sneak preview his series of F# articles and they are very good. I took one of his examples and modified it a bit. The following code displays "sum = 6", but how that happens is other-worldly...check it out:
#light
let rec sum nums =
match nums with
| head::tail -> head + sum(tail)
| [] -> 0
printf "sum = %i" (sum [1; 2; 3])Weird, eh? F# is coooool. :cool:
:josh: My WPF Blog[^] Without a strive for perfection I would be terribly bored.
I just don't get the point of yet another functional language before all those 'mainstream' FPs such as Haskell or Scheme become widely accepted by programmers. They have developed over 10 years and are much more mature than this F# thing, which by the look of this tiny program, is not syntactically attractive at all compared with those mentioned above. And I simply don't like their attitudes of trying to 'go mainstream' by the support of .Net while ignoring the efforts and accomplishments already put and gained in the functional programming area.
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I've been studying F# a lot recently and find it really mind-bending. Tomas Petricek, a fellow CPian, let me sneak preview his series of F# articles and they are very good. I took one of his examples and modified it a bit. The following code displays "sum = 6", but how that happens is other-worldly...check it out:
#light
let rec sum nums =
match nums with
| head::tail -> head + sum(tail)
| [] -> 0
printf "sum = %i" (sum [1; 2; 3])Weird, eh? F# is coooool. :cool:
:josh: My WPF Blog[^] Without a strive for perfection I would be terribly bored.
Josh, There are always people to make up a new language to do something, but no one to modify an existing language to do that too. Some things cannot be accomplished in previous languages, but I believe there is alot that can be done, instead of making up a new language, and then the creators of that language have to come up with terms no one understands because the words used are not used the same way in that language. *taking a breath right now* F# looks like APL, and LISP and Haskell, etc... I agree with some of the newer ideas about iterative approaches, but someone HAS to be smart enough to be able to present it clearly and in a maintainable manner in a language. I think that's a summary of all of the posts. No one can comment on the language because you haven't spelled out what each line is accomplishing. If you did that, then you may be able to move people to look into the language further. To me its just another language that is either so specialized we'll never use it or another one of the languages that proclaims itself to be able to kill all other languages. I still use C alot. Supposed to be killed by C++, which was killed by Java which was killed by C# which only runs on one platform with work being partly done on another platform. Ruby is a web language killer, whereas Python was supposed to be, PHP before that, and Perl. The cynic rests his case.
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Superb, just a couple of possible improvements that could be made: 1) Replace all readable characters with further punctuation marks 2) Put a C somewhere in the name of the language and hey presto - mainstream! Rich
I second that, except make the Space character a functional part of the language. Why relegate the lonely space to nullability? Who played God and said the space was just a holding character? I make a motion that all spaces be removed and that the space become the "If" in the conditional statement. I further motion that W replace the space and a lowly holding character. Sample code: wwww ;=1w)=)+23 wwww#)=2 Could be written to make it pretty wwww ;w=w1w)w=w)w+w23 wwww#w)w=w2 That says if semicolon equals one then right parenthesis equals right parenthesis plus twenty three else right parenthesis equals two. OHHHH the elegance of it all. It is so clear and maintainable.
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More like waking up the next morning and wondering what species is laying next to you.
Software Zen:
delete this; -
It's for problems where you indicate what you want performed on every member of a list (map) or how you aggregate the contents of a list (reduce). In theory, because each of the operations is atomic (independent of the other items), in the case of the map operation, or the result of reducing the whole list is the same as reducing distinct subparts of the list then reducing the results of those suboperations, you can farm out subparts of the list to other cores to execute in parallel. Because it's implicit, the environment can scale the algorithm appropriately to the number of installed cores. Still, it's not much that a parallel foreach couldn't do. It's just we're not used to writing our programs as such discrete blobs of functionality, effectively putting half your program out-of-line. And I'm not sure that many of the programs we regularly use would benefit - your data set would have to be pretty big to overcome the cost of the inter-thread procedure calling required to get another core working on part of the problem. I'm not totally sure the MHz myth is as over as it seemed a few years ago. The 45nm generation with high-k dielectric looks like it may have solved or at least alleviated the leakage problems that caused such trouble with overheating when trying to ramp up the clock speeds. The Core 2 Duo E8500 is supposed to clock at 3.16GHz while keeping a Thermal Design Power of 65W (source[^]).
DoEvents: Generating unexpected recursion since 1991It's impossible to express better the right concept, but let me a bit more. F# is a functional programming language and this is its goal. But unfortunatly I think programmers will wanna take less time to deploy the application but they will take more time to thinking with this logic, more time to undestend after few months, more pc power... You can choose when use this or another language thinking in this.
Dr.Luiji Trust and you'll be trusted.
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I've been studying F# a lot recently and find it really mind-bending. Tomas Petricek, a fellow CPian, let me sneak preview his series of F# articles and they are very good. I took one of his examples and modified it a bit. The following code displays "sum = 6", but how that happens is other-worldly...check it out:
#light
let rec sum nums =
match nums with
| head::tail -> head + sum(tail)
| [] -> 0
printf "sum = %i" (sum [1; 2; 3])Weird, eh? F# is coooool. :cool:
:josh: My WPF Blog[^] Without a strive for perfection I would be terribly bored.
-
I've been studying F# a lot recently and find it really mind-bending. Tomas Petricek, a fellow CPian, let me sneak preview his series of F# articles and they are very good. I took one of his examples and modified it a bit. The following code displays "sum = 6", but how that happens is other-worldly...check it out:
#light
let rec sum nums =
match nums with
| head::tail -> head + sum(tail)
| [] -> 0
printf "sum = %i" (sum [1; 2; 3])Weird, eh? F# is coooool. :cool:
:josh: My WPF Blog[^] Without a strive for perfection I would be terribly bored.
Oh man ... I thought Turbo Pascal was dead! -CB ;)
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Josh Smith wrote:
There's nothing better than freeing your mind a little bit,
As long as it does not fall out and get lost in the process :)
Rocky <>< Blog Post: MVC for ASP.NET! Tech Blog Post: Cheap Biofuels and Synthetics coming soon? Tech Sites: SilverlightCity.com ~ TheSilverlightDirectory.com ~ TheWPFDirectory.com
Josh Smith wrote: There's nothing better than freeing your mind a little bit, Rocky Moore wrote: As long as it does not fall out and get lost in the process As a wiseman(?) once about his mind wandering: "Don't worry, its small and feeble and can't get far." ;P:laugh: