<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
Hey guys,<br>
This conversation is really interesting. I am not a haskell expert
(I haven't progressed into monads in haskell yet, and have only
briefly studied the state monad in scala. Studying fp concepts has
changed the way I think about problems that are complicated. I am
not quite there yet, (I still catch myself updating states when I
don't need to) and wondering how the hell to break a problem into
recursive little bits. I now notice that I am less tempted to do
things that would have bugs in complicated data structures , prefer
map to do something to a list, and folds to for loops that update a
``state'' variable, and finally, I can reason about where the weak
points in my code may be. The learning I have achieved do to fp, and
my principals of programming languages class that relied on fp, have
made doing things with code easier because I don't try to do stupid
things like overrun the end of an array with a misplaced loop
counter variable. It is way too easy to learn fold, filter, map, and
list comprehensions, you then have a powerful weapon to use against
those ugly off by one errors. <br>
Also, I learned how people who learned programming in
non-traditional languages might think to approach problems earlier
this year. My stats professor was showing us things in r. She showed
us a complicated set of formula that we needed to do, and then
explained we were calculating something to each element of a list.
She showed a function sapply(vector, function(elem)) that returns a
vector. She said to think about how sapply applies that function to
each vector element, and returns the transformed list. She didn't
approach it as if it were this big bad function that takes a
function, mainly i think because she hadn't learned programming from
people who insist on the idea of c. It also really made sense to the
class who mainly had little to no programming experience, where
explaining a for loop in all it's glory would normally take a couple
of lectures. She is a really solid programmer and really understands
how to use programming to solve real world problems, so I am not
saying that she didn't know enough to have not learned for loops,
just that she immediately realized that the sapply function really
was better for the situation. If we teach people these patterns from
the get go, I think some of the horror of learning functional
programming would be solved because the number of applications that
a generic function can be applied in far outnumbers the number of
cases a for loop or state momad is needed. I would also now argue
that all data structures classes should be taught in functional
programming languages. I never solidly understood trees and could
confidently traverse and change them until I actually got introduced
to pattern matching and folds. I was taught binary search trees, and
red-black trees, and worked with tree like structures, but it was
always hard for me to comprehend how to do things with them. I
learned linked lists in c++ but hated them with a passion because I
had to write forloops that updated a temporary variable and write
while loops that did the same, but often jumped off the end of the
list and then I couldn't go back. The beauty of recursion and lists
is that recursion allows you to backtrack when things go wrong (as
they always will for any real input in a program). The second I
learned about Haskell for the first time, linked list traversing
became second nature to me, even in non-functional (inferier) c++.
The argument that "recursion results in overriding the stack" is
kind of a flawed one since the compiler wizards have figured out
ways to optimize tail recursive functions to do exactly what we
humans are bad at (running recursive functions as if they were
unrolled, with large inputs, and fast). <br>
Thanks,<br>
Derek<br>
<br>
<div class="moz-cite-prefix">On 12/11/2015 11:32 AM, Thomas Jakway
wrote:<br>
</div>
<blockquote
cite="mid:8d5e544f-2ee7-473d-a2bf-5fea3e73fa62@email.android.com"
type="cite">
<pre wrap="">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 <a class="moz-txt-link-rfc2396E" href="mailto:matthewjwilliams101@gmail.com"><matthewjwilliams101@gmail.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">
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 <a class="moz-txt-link-rfc2396E" href="mailto:bergey@alum.mit.edu"><bergey@alum.mit.edu></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">On 2015-12-11 at 10:07, Abhishek Kumar <a class="moz-txt-link-rfc2396E" href="mailto:abhishekkmr18@gmail.com"><abhishekkmr18@gmail.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">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.
</pre>
</blockquote>
<pre wrap="">
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:
<a class="moz-txt-link-freetext" href="http://chimera.labs.oreilly.com/books/1230000000929">http://chimera.labs.oreilly.com/books/1230000000929</a>
bergey
Footnotes:
[1] OK, many changes.
_______________________________________________
Beginners mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Beginners@haskell.org">Beginners@haskell.org</a>
<a class="moz-txt-link-freetext" href="http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners">http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners</a>
</pre>
</blockquote>
<pre wrap="">_______________________________________________
Beginners mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Beginners@haskell.org">Beginners@haskell.org</a>
<a class="moz-txt-link-freetext" href="http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners">http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners</a>
</pre>
</blockquote>
<pre wrap="">_______________________________________________
Beginners mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Beginners@haskell.org">Beginners@haskell.org</a>
<a class="moz-txt-link-freetext" href="http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners">http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners</a>
</pre>
</blockquote>
<br>
<div class="moz-signature">-- <br>
<hr>
<h2 style="text-size:24px;"> Derek Riemer </h2>
<ul>
<li> Department of computer science, third year undergraduate
student. </li>
<li> Proud user of the NVDA screen reader.</li>
<li> Open source enthusiast.</li>
<li> Member of Bridge Cu </li>
<!-- <li> Member of the Council for Inclusion, Leadership, and advocacy. </li> -->
<li> Avid skiier.</li>
</ul>
<p> Websites: <br>
<a href="http://derekriemer.drupalgardens.com">Honors portfolio</a>
<br>
<a href="http://derekriemer.pythonanywhere.com/personal">
Non-proffessional website.</a> <br>
<a href="http://derekriemer.pythonanywhere.com/weather">Awesome
little hand built weather app that rocks!</a> <br>
</p>
<p>
<a href="mailto:derek.riemer@colorado.edu"> email me at
derek.riemer@colorado.edu</a>
<br>
Phone: (303) 906-2194
</p>
</div>
</body>
</html>