[Haskell-beginners] Doubts about functional programming paradigm

[Thomas Jakway]

Building on that, I think coming to Haskell with a very specific goal in mind (like swap Haskell for Java in my map reduce problem) kind of misses the point.  Haskell may or may not be faster/better suited to map reduce vs Java, but the real reason to use/learn Haskell is elegance and correctness.  The lack of side effects and referential transparency means you're far more likely to prevent bugs.  And there's a pretty substantial learning curve coming from imperative languages so if you need to speed up map reduce on a deadline you will be more productive in the imperative language of your choice (for now).

Dont take this as discouragement, I think Haskell (and FP in general) is very well suited to that kind of problem.  I'm a beginner in Haskell and it's already had a huge impact on how I think about all the code I write, not just the occasional toy Haskell project.

On Dec 11, 2015 1:08 PM, MJ Williams <matthewjwilliams101 at gmail.com> wrote:
>
> A pure functional language enables you to reason about your code, 
> something you can't easily achieve with your average C or Java. And by 
> `reason' I am referring to mathematical proof. Haskell makes it very 
> simple, actually.  Why should you want to reason about your code? 
> Think the hassle you could avoid if you knew what your code really 
> meant and did when executed. 
>
> The absence of side effects is part of another concept in FP, namely, 
> `referential transparency'.  If your function `f' maps a value `x' to 
> a value `y' then `f x' will always equal `y' and no more. In other 
> words, your function `f' won't change anything e.g. assign to 
> variables, or other state changes as well as mapping `x' to `y', and 
> that's an absolute certainty, in theory, at any rate. 
>
> That's a very crude overview of at least part of what functional 
> programming is about.  I'm hoping it'll encourage others on this list 
> with far more in-depth knowledge of the subject matter to come in and 
> fill in the gaps and iron out the ambiguities. 
>
> Matthew 
>
>
> On 11/12/2015, Daniel Bergey <bergey at alum.mit.edu> wrote: 
> > On 2015-12-11 at 10:07, Abhishek Kumar <abhishekkmr18 at gmail.com> wrote: 
> >> I am a beginner in haskell.I have heard a lot about haskell being great 
> >> for 
> >> parallel programming and concurrency but couldn't understand why?Aren't 
> >> iterative algorithms like MapReduce more suitable to run parallely?Also 
> >> how 
> >> immutable data structures add to speed?I'm having trouble understanding 
> >> very philosophy of functional programming, how do we gain by writing 
> >> everything as functions and pure code(without side effects)? 
> >> Any links or references will be a great help. 
> > 
> > Functional languages make it easy to decompose problems in the way that 
> > MapReduce frameworks require.  A few examples (fold is another name for 
> > reduce): 
> > 
> > sum :: [Double] -> Double 
> > sum xs = foldr (+) 0 xs 
> > 
> > sumSquares :: [Double] -> Double 
> > sumSquares xs = foldr (+) 0 (map (**2) xs) 
> > 
> > -- foldMap combines the map & fold steps 
> > -- The Monoid instance for String specifies how to combine 2 Strings 
> > -- Unlike numbers, there's only one consistent option 
> > unlines :: [Text] -> Text 
> > unlines xs = foldMap (`snoc` '\n') xs 
> > 
> > We'd need a few changes[1] to make this parallel and distribute across many 
> > computers, but expressing the part that changes for each new MapReduce 
> > task should stay easy. 
> > 
> > Immutable data by default helps with concurrency.  Speed may or may not be 
> > the goal.  We want to be able to distribute tasks (eg, function calls) 
> > across processor cores, and run them in different order, without 
> > introducing race conditions. 
> > 
> > Simon Marlow's book is great at explaining parallel & concurrent 
> > concepts, and the particular tools for applying them in Haskell: 
> > http://chimera.labs.oreilly.com/books/1230000000929 
> > 
> > bergey 
> > 
> > Footnotes: 
> > [1]  OK, many changes. 
> > 
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> > 
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