It also allows cool things such as infinite data structures.
Haskell tutorial series#
That goes well with referential transparency and it allows you to think of programs as a series of transformations on data. That means that unless specifically told otherwise, Haskell won't execute functions and calculate things until it's really forced to show you a result. That's called referential transparency and not only does it allow the compiler to reason about the program's behavior, but it also allows you to easily deduce (and even prove) that a function is correct and then build more complex functions by gluing simple functions together. At first, this seems kind of limiting but it actually has some very nice consequences: if a function is called twice with the same parameters, it's guaranteed to return the same result. The only thing a function can do is calculate something and return it as a result. What are you, some kind of liar? So in purely functional languages, a function has no side-effects. If you say that a is 5, you can't say it's something else later because you just said it was 5. You also can't set a variable to something and then set it to something else later. You express that in the form of functions.
Haskell tutorial plus#
The factorial of a number is the product of all the numbers from 1 to that number, the sum of a list of numbers is the first number plus the sum of all the other numbers, and so on. In purely functional programming you don't tell the computer what to do as such but rather you tell it what stuff is. You have control flow structures for doing some action several times. For instance, you set variable a to 5 and then do some stuff and then set it to something else. While executing them, it can change state. In imperative languages you get things done by giving the computer a sequence of tasks and then it executes them. Haskell is a purely functional programming language. Learning Haskell is much like learning to program for the first time - it's fun! It forces you to think differently, which brings us to the next section … I guess what I'm trying to say is: Haskell is great and if you're interested in programming you should really learn it even if it seems weird at first. But then once it just "clicked" and after getting over that initial hurdle, it was pretty much smooth sailing. I failed to learn Haskell approximately 2 times before finally grasping it because it all just seemed too weird to me and I didn't get it. People there are extremely nice, patient and understanding to newbies. The channel #haskell on the freenode network is a great place to ask questions if you're feeling stuck. Although I bet that even if you don't have any significant programming experience, a smart person such as yourself will be able to follow along and learn Haskell. This tutorial is aimed at people who have experience in imperative programming languages (C, C++, Java, Python …) but haven't programmed in a functional language before (Haskell, ML, OCaml …). So this is an attempt at adding another useful resource for learning Haskell so you have a bigger chance of finding one you like. By going through several resources, I was able put together the pieces and it all just came falling into place. The way I learned it was by reading several different tutorials and articles because each explained something in a different way than the other did.
When I was starting out in Haskell, I didn't learn from just one resource. There are quite a few tutorials on Haskell floating around on the internet.
I decided to write this because I wanted to solidify my own knowledge of Haskell and because I thought I could help people new to Haskell learn it from my perspective. Well, you've come to the right place, but let's talk about this tutorial a bit first. If you're reading this, chances are you want to learn Haskell. *ValueExpressions> H.runTestTT $ H.Welcome to Learn You a Haskell for Great Good! Compiling Main ( GettingStarted.lhs, interpreted )ĬaseValue2 :: Parser ValueExpr -> Parser ValueExpr caseValue2 val = do trace "start case" $ return () void $ keyword "case" trace "read case keyword" $ return () testExp False _ -> True return v Compiling FunctionsAndTypesForParsing ( FunctionsAndTypesForParsing.lhs, interpreted ) Compiling ( Text/Parsec/String/Parsec.hs, interpreted ) Compiling ( Text/Parsec/String/Combinator.hs, interpreted ) Compiling ( Text/Parsec/String/Char.hs, interpreted ) Working v1- use case with the new-style commands. Please file a bug if you cannot replicate a Or the legacy v1-repl alias as new-style projects will become the default in
Please switch to using either the new project style and the new-repl command Warning: The repl command is a part of the legacy v1 style of cabal usage.
Haskell tutorial code#
updated parsing code with improved error message behaviour how parsec combines errors or drops them into the void operator table and the first value expression parser
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