Friday, December 21, 2007

My Type of Language...

Ok as I stated I'm not a Lisp zealot which language am I advocating?

Haskell!

Am I saying it is perfect? No
Is it going to be the Next Big Language? I wish... but No
Is it a silver bullet? No

Then why?

Some smart dude already said that learning Lisp, even if you never use it would make you a better programmer. I don't disagree with that statement but I'd say that it is an order of magnitude truer with Haskell.

The purity of Haskell forces you to think differently. You can't revert to do thing procedurally at least not easily. In fact, I'd say that by the time you know enough Haskell to code procedurally you will not want to do so anymore!

Ok it's pure... What else? It is lazy... this allows it to be even more declarative than other FP language and it also helps even more to separate what you want to do from HOW you do it.

By the way, bear with me on those characteristics I am pointing out, I'll be revisiting them in future posts.

Finally I'd say it's type system will open your mind forever. Haskell is not the only language using Hindley-Milner type system, static type inference, BUT it has Type Classes which makes this type system much more expressive and feel much less "constraining" than the version of H-M in Ocaml for example. Any languages of the ML family (they all have H-M type system) will grow you a third eye: a new axis to design and encode semantics.

What makes Haskell so special is that its version of H-M, it's purety and its lazyness will make you learn a lots of new tricks and bring you to a deeper understanding of all programming languages not just functionals ones, C++ and Java too.

Once you have learned Haskell I'd say you are in a better position to appreciate PL in generals. In my case I love Haskell but I tend to appreciate Scheme and Common Lisp in a different way now that I know Haskell.

More Haskell ramblings to come in future post but for now I'm finishing this post with my personal recipe to learn Haskell. This is an email I sent to a few friend:

Hello all,
 
I’ve been asked a few times lately about reference or how to learn Haskell. In case it is useful (or of interest) I’m forwarding here the informations I sent to a friend. This is by no means the only way to learn the language but in my experience this recipe is the “smoothest” ride to learn Haskell.
 
 
First a brief explanation why the language is SO different:
 
- There is NO variable, anytime you assign a value it is immutable. (mostly true of ML family languages like Ocaml)
- Purely Functional i.e. there is NO sequencing of operation (outside of Monads)
- Lazy Evaluation, if you call a function with 3 parameters the parameters WILL NOT be evaluated before you enter the function, only if they are used. Laziness allows a LOT of very clever and useful tricks.
- Referential Transparent, if you see a function called with specific arguments then EVERY TIME it is called with the same arguments it will return the SAME value.
 
In C++/Java, you design your Data Structure and you’re interaction between object, sometimes people design dataflow too.
In Haskell you have 2 additional and mostly orthogonal design Axis: Typing and combinators. Typing is a rather big one, in term of expressiveness. The more you’ll learn Haskell and the deeper your understanding of programming language becomes, including those of C++ and Java languages, this is especially true of template and the reason of their limitation. The second “new axis” is combinator, due to FP, currying (you’ll learn the word soon enough ;) ) you end up separating the pattern of processing for ONE instance and pattern of processing over Collection. The result is much more reusable code and a “by-layer” approach. The more a program grows the less code you have to write to add new features and or to modify to refactor, since your palette of combinator and of transformation becomes very complete.
 
 
To “learn” Haskell you need to learn roughly along 4 new “axis” or paradigms. Right now, no single book or paper covers these aspects. They are:
 
1. Functional Programming and mastering recursion in particular (FP)
2. Very strong typing with type inference (Hindley-Milner typing system). Which is used in all the language of the ML family (Ocaml, SML, ML and also in Haskell) always coupled with immutable variable i.e. constant.
3. Learn to type, i.e. to design the Type of what you are building. It is related to point number 2, but whereas point number 2 concerns the usage and implication of strong statically inferred types. This point refers to actually using typing as a mean to store information, logic and semantic in a program.
4. Monads. This is related to 1. (FP) but it is more advanced, and required in Haskell whereas it is optional for other functional language. This is a consequence of the purity of Haskell. Monads are GREAT, the more you know them the more you love them BUT… they are alien to our usual way of thinking.
 
To Learn Haskell efficiently and as easily as possible here’s what I suggest.
Point 1. Learning FP, read the book “The Little Schemer” and do all the exercise as you read. This book will bake basic recursive thinking in your brain and will introduce you to collectors function and how to combine functions together and accumulate functions to build new ones. This part will help to groke Monads (point 4.)
By the way no knowledge at all is assume to read this book. Your mom could!
To do the exercise as you go along I recommend picking PLT-Scheme

Point 2. The easiest way here is to do a simple tutorial in Ocaml or SML. Why? To not be distracted by laziness issues. Jason Hickey's Ocaml tutorial here is the one I began with. It also shows some twist about how recursions and FP work in Ocaml. Note that neither Ocaml nor SML are purely functional and you can actually code procedurally in both and “almost” object in Ocaml. The reason why I like this tutorial is because it is a more traditional format and use both functional and procedural and rather concentrate on typing, type deconstruction etc which all works in Haskell.

Point 3. The best way and by far to learn this is through the book “Haskell School of Expression” the book is VERY good to bring you to use the typing system as a design mean and the way it is written is interesting. You basically build a graphical object manipulation framework! Well written, well pace and easy to understand. It progressively introduces a lot of things. Its Monad introduction is too shallow, when he starts using them toward the end of the book you may have to stop and read a few paper to grasp what is there in order to continue. Once you understand the basics of the Monads, the State Monad exemple he uses is very good to build our understanding (he build a robot using the State Monad).

Point 4. That’s the hard one. Because of the different background we all have people don’t always get stuck at the same spot when understanding them. I consider them relatively easy to learn with “support” i.e. someone to explain the hard part, and VERY HARD to learn by oneself depending on what part you are blocked on. Why? Because most of the information on them is either on research paper or in very simple tutorials (too simple). So if there is something you don’t understand there is NO middle level reading that can help you (if you go by yourself) and the only chose is to resort to read research papers, typically many of them to see them present and attack the subject on differents angles until you find the one that “unlock” you. For exemple, by myself with nobody to answer my questions and just the research papers. It took me over 6 months to “taste” most of the subtilities of some Monads, State Monad in particular. Whereas I can explain the basic of it in less than one hour to anybody starting Haskell… Maybe it’s just me! By the way, a bone here :P Monads are the kings of combination they are themselves combinator!!!

The Point 1 to 3 can very easily be done without any support, through self-learning. Point 4, well… call me ;)

Cheers!

1 comment:

Jocelyn Legault said...

Hello JF.

Glad you took the time to get a new entry in your blog! Gee, I wish you could get a new one every week! ;-)

BTW, I still haven't had the time to get back to TLS since I moved out west. I should be able to get back to it in a few weeks. The next step being lambda functions and the dreaded "... and again, and again...", I might have to call on you to clarify some points.

cheers!

joce.