Functional Programming 101 with Haskell

http://blog.gja.in/2014/01/functional-programming-101-with-haskell.html

by Who828 • 13 years ago

94 40 13 years ago

blog.gja.in

MaxGabriel• 13 years ago

For a 101, you may want to direct readers to install Haskell Platform as an easy way to get GHCI and all that set up.

tdinkar3• 13 years ago

Thanks for this, I added a link in the bottom.

jamesbritt• 13 years ago

... I added a link in the bottom.

Perhaps helping users get set-up should be the first thing you address.

Also, you start off by saying the examples should work well in ghci but then show examples that are not run in ghci.

I fear your experience is blinding you to the numerous little things that trip up newcomers.

You might also state upfront what you assume the reader already knows. Such as the existence, and use, of ghci.

If you are mentioning ghci at the start then maybe show the examples as run in ghci. Or, if you prefer files, then explain how to run a file from the command line.

carterschonwald• 13 years ago

Also you should make sure that those who hit the cpp problem don't get overwhelmed. I've actually spent some time this week working out a patch that will make the cpp problem tst hit OS X IMPOSSIBLE to have in the future. Did require learning some autoconf thogh :-)

hamburglar3• 13 years ago

As a complete and total haskell noob, I am unable to even get through your syntax examples:

Prelude> sumOfElements [] = 0

<interactive>:12:18: parse error on input `='

tdinkar3• 13 years ago

Start with downloading the hydra.hs file I linked to in the end.

Haskell is not like ruby, it's a bit harder to define functions in the interpreter. It's easier to put them in a .hs file and then :load file.hs

navbaker• 13 years ago

Since this is a 101, you might want to put your Haskell setup URL and any file dependencies/explanations of Haskell's idiosyncrasies at the top of the tutorial. A 101 is aimed at people who don't know anything about the language and assuming knowledge is a good way to ensure folks get frustrated and never come back.

coolsunglasses2• 13 years ago

You're using the REPL, where every operation is basically happening in a do monad.

If you get an error like that where you intend to define something, use let.

like: let sumOfElements [] = 0

gizmo6862• 13 years ago

I believe you mean that every operation is happening in the IO monad, and you input is being interpreted as if it was in a do block.

gizmo6862• 13 years ago

This defiantly falls under Haskell not being noob friendly.

If you are in the REPL, you want to do `let sumOfElements [] = 0`

If you want multiline input, you open with `:{` and close with `:}`. Both of these need to be on their own line. For example:

    Prelude>:{
    Prelude| let sum [] = 0
    Prelude|     sum (x:xs) = x + sum xs
    Prelude|:}

As tdinkar points out, it is often easier to define your functions if a file and load that file from the REPL.

hamburglar3• 13 years ago

aha, i tried using 'let' on the assumption that he was just being brief, but I put a 'let' in front of each of the pattern-matching function signatures, which didn't work. Thanks.

edit: I take your last comment as "when using the REPL, it is easier not to use the REPL." :D

andrus• 13 years ago

Neat, I knew about `:set +m` for enabling multiline input, but not `:{ ... }:`.

freyrs32• 13 years ago

The equivalent chapter in Learn you a Haskell is probably a better place to learn about list processing in Haskell.

http://learnyouahaskell.com/starting-out#an-intro-to-lists

idProQuo2• 13 years ago

Having finally finished my first read of LYAH (It took me months of reading, practicing and taking breaks to let it all sink in), I can only see one way to improve upon it: Make a video series.

I don't know enough about Haskell to pull it off (though I may try if no one's done it in a year or so). However if someone could inject the wacky sensibility* of things like LYAH, Computerphile and CodeSchool.com into a Haskell video tutorial, it would do worlds of good for the community. Better yet, if someone could make an interactive class like CodeSchool or Codecademy, that would be amazing.

* Thought I should mention that the wackiness isn't the only important part, it also needs to be properly paced. That was LYAH's other strong point, they hammer home each concept with multiple examples before moving on.

freyrs32• 13 years ago

A video series or course on LYAH would be an amazing resource. On an aside, there's a bunch of great intermediate level video tutorials working through various projects here:

[1] https://www.youtube.com/user/jekor/videos

laureny• 13 years ago

Having finally finished my first read of LYAH (It took me months of reading, practicing and taking breaks to let it all sink in), I can only see one way to improve upon it: Make a video series.

Why? I can't think of any advantage that a video has over an article when it comes to teaching computer science. An article allows me to read and understand each concept at my own pace and rereading something I didn't quite get is trivial. All these simple things are just tedious with a video.

vasquez2• 13 years ago

I think this 13-part series by Erik Meijer is great: http://channel9.msdn.com/Series/C9-Lectures-Erik-Meijer-Func...

More material here: http://www.haskell.org/haskellwiki/Video_presentations#Intro...

chilldream• 13 years ago

https://www.fpcomplete.com/ is trying to do this

res0nat0r• 13 years ago

I'll chime in and mention that Learn You A Haskell is the best online Haskell tutorial I've found. I've been working through bits of it the last couple of weeks and it is excellent.

Also the artwork is great.

http://learnyouahaskell.com/

asattarmd• 13 years ago

The best intro for functional programming, IMO, is Joel Spolsky's "Can your language do this" (http://www.joelonsoftware.com/items/2006/08/01.html).

copx• 13 years ago

Every newer language can do "this". First class functions and anonymous functions have been a standard feature for a while. Does not mean that say Lua or Ruby are functional programming languages. If you just require the ability to pass around anonymous functions even C++ is a functional programming language these days.

To meaningfully distinguish functional from imperative programming you have to add purity/immutable data to the definition at least.

euph0ria2• 13 years ago

Why is it not n! ?

tdinkar3• 13 years ago

It's actually 9* (1 + 8 * (1 + 7 * (1 + 6 ..... + 1)))

winstonsmith2• 13 years ago

= [9!e] - 1

(because your expression expands to 9 + 9(8) + 9(8)(7) + ... 9! = 9!(1+1/1 + 1/2! + ... 1/8!) = -1 + 9! e - (1/10 + 1/(10 11) + ...))

nbouscal• 13 years ago

There will be n! of the smallest heads, the ones which don't spawn any new heads. Total heads, though, will be 9 + 9 * 8 + 9 * 8 * 7 + ...

euph0ria2• 12 years ago

aargh, of course... thanks!

winstonsmith2• 13 years ago

It's actually [n!e] - 1 where [x] the greatest integer less than or equal to x and e is the base of the natural logarithm. As nbouscal points out, the total number of heads is H=n!(1+1/1!+ 1/(n-1)!). Using the Taylor series for e^x, H = n!e - n!(1/n! + 1/(n+1)! + ...) = n!e - 1 - r, where r = (1/(n+1) + 1/(n+1)(n+2) ...). The remainder term r is easily seen to be less than 1, and H is and integer, so H=[H+r]=[n!e]-1.

coldcode• 13 years ago

Every time I see Haskell I am reminded of programming in Forth for some reason.

codygman2• 13 years ago

Perhaps because of point free style?

Functional Programming 101 with Haskell

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