Difference between revisions of "Ja/Haskell入門 5ステップ"
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| − | Haskell is a general purpose, purely functional programming language. |
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| − | This page will help you get started as quickly as possible. |
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| − | |||
| − | __TOC__ |
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| − | |||
| − | == Install Haskell == |
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| − | |||
| − | Haskell, like most other languages, comes in two flavors: batch oriented |
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| − | (''compiler'') and interactive (''interpreter''). An interactive system |
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| − | gives you a command line where you can experiment and evaluate |
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| − | expressions directly, and is probably a good choice to start with. |
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| − | |||
| − | {| class="wikitable" |
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| − | |[http://www.haskell.org/ghc/ GHC] |
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| − | |Compiler and interpreter (GHCi) |
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| − | |Probably the most feature-complete system |
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| − | |- |
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| − | |[http://www.haskell.org/hugs/ Hugs] |
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| − | |Interpreter only |
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| − | |Very portable, and more lightweight than GHC. |
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| − | |} |
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| − | |||
| − | While both GHC and Hugs work on Windows, Hugs has perhaps the best |
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| − | integration on that platform. Nonetheless, GHC is more actively developed and maintained, and the consensus seems to be that it is the generally-recommended environment of choice for newcomers to Haskell as well as old hands. There is also information available on |
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| − | [[Mac OS X|installing Haskell software on Mac OS X]]. |
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| − | |||
| − | == Start Haskell == |
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| − | |||
| − | Open a terminal. If you installed GHC, type '''ghci''' (the name of the executable of the GHC |
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| − | interpreter) at the command prompt. If you installed Hugs, type '''hugs'''. |
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| − | |||
| − | <pre> |
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| − | $ ghci |
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| − | ___ ___ _ |
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| − | / _ \ /\ /\/ __(_) |
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| − | / /_\// /_/ / / | | GHC Interactive, version 6.4, for Haskell 98. |
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| − | / /_\\/ __ / /___| | http://www.haskell.org/ghc/ |
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| − | \____/\/ /_/\____/|_| Type :? for help. |
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| − | |||
| − | Loading package base-1.0 ... linking ... done. |
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| − | Prelude> |
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| − | </pre> |
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| − | |||
| − | And you are presented with a prompt. The Haskell system now attentively |
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| − | awaits your input. |
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| − | |||
| − | == Write your first Haskell program == |
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| − | |||
| − | If you've learned to program another language, your first program |
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| − | probably was "Hello, world!", so let's do that: |
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| − | |||
| − | <haskell> |
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| − | Prelude> "Hello, World!" |
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| − | "Hello, World!" |
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| − | </haskell> |
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| − | |||
| − | The Haskell system evaluated the string, and printed the result. |
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| − | Or we can try a variation to print directly to standard output: |
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| − | |||
| − | <haskell> |
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| − | Prelude> putStrLn "Hello World" |
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| − | Hello World |
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| − | </haskell> |
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| − | |||
| − | Using a Haskell compiler, such as [http://haskell.org/ghc GHC], you can |
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| − | compile the code to a standalone executable. Create a source file |
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| − | '''hello.hs''' containing: |
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| − | |||
| − | <haskell> |
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| − | main = putStrLn "Hello, World!" |
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| − | </haskell> |
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| − | |||
| − | And compile it with: |
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| − | |||
| − | <pre> |
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| − | $ ghc -o hello hello.hs |
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| − | </pre> |
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| − | |||
| − | You can then run the executable ('''./hello''' on Unix systems, '''hello.exe''' on Windows): |
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| − | |||
| − | <pre> |
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| − | $ ./hello |
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| − | Hello, World! |
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| − | </pre> |
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| − | |||
| − | == Haskell the calculator == |
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| − | |||
| − | Let's do something fun. In Haskell, your first true program is the |
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| − | factorial function. So back to the interpreter now and let's define it: |
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| − | |||
| − | <haskell> |
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| − | Prelude> let fac n = if n == 0 then 1 else n * fac (n-1) |
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| − | </haskell> |
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| − | |||
| − | This defines a new function called '''fac''' which computes the |
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| − | factorial of an integer. |
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| − | |||
| − | We can now run '''fac''' on some argument: |
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| − | <haskell> |
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| − | Prelude> fac 42 |
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| − | 1405006117752879898543142606244511569936384000000000 |
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| − | </haskell> |
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| − | |||
| − | '''Congratulations!''' Programming made easy. Note that if you're using |
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| − | Hugs, you'll need to load the definition of '''fac''' from a file, |
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| − | '''fac.hs''', containing: |
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| − | |||
| − | <haskell> |
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| − | fac n = if n == 0 then 1 else n * fac (n-1) |
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| − | </haskell> |
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| − | |||
| − | And run it with Hugs as follows (this also works in GHCi): |
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| − | |||
| − | <haskell> |
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| − | Hugs.Base> :load fac.hs |
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| − | Main> fac 42 |
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| − | 1405006117752879898543142606244511569936384000000000 |
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| − | </haskell> |
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| − | |||
| − | We can of course compile this program, to produce a standalone |
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| − | executable. In the file '''fac.hs''' we can write (and let's use |
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| − | elegant pattern matching syntax just for fun): |
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| − | |||
| − | <haskell> |
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| − | fac 0 = 1 |
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| − | fac n = n * fac (n-1) |
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| − | |||
| − | main = print (fac 42) |
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| − | </haskell> |
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| − | |||
| − | which can then be compiled and run: |
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| − | |||
| − | <pre> |
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| − | $ ghc -o fac fac.hs |
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| − | $ ./fac |
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| − | 1405006117752879898543142606244511569936384000000000 |
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| − | </pre> |
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| − | |||
| − | '''Great!''' |
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| − | |||
| − | ===Write your first parallel Haskell program=== |
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| − | |||
| − | Haskell has good support for parallel and multicore programming. We can write a parallel program by adding `par` to expressions, like so: |
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| − | |||
| − | <haskell> |
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| − | import Control.Parallel |
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| − | |||
| − | main = a `par` b `par` c `pseq` print (a + b + c) |
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| − | where |
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| − | a = ack 3 10 |
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| − | b = fac 42 |
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| − | c = fib 34 |
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| − | |||
| − | fac 0 = 1 |
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| − | fac n = n * fac (n-1) |
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| − | |||
| − | ack 0 n = n+1 |
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| − | ack m 0 = ack (m-1) 1 |
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| − | ack m n = ack (m-1) (ack m (n-1)) |
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| − | |||
| − | fib 0 = 0 |
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| − | fib 1 = 1 |
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| − | fib n = fib (n-1) + fib (n-2) |
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| − | </haskell> |
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| − | |||
| − | Compiling with -threaded and optimizations on: |
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| − | |||
| − | <pre> |
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| − | $ ghc -O2 --make A.hs -threaded |
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| − | [1 of 1] Compiling Main ( A.hs, A.o ) |
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| − | Linking A ... |
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| − | </pre> |
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| − | |||
| − | And now we can run our multicore program. Here across two cores: |
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| − | |||
| − | <pre> |
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| − | $ time ./A +RTS -N2 |
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| − | 1405006117752879898543142606244511569936384005711076 |
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| − | ./A +RTS -N2 2.14s user 0.02s system 149% cpu 1.449 total |
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| − | </pre> |
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| − | |||
| − | Congratulations! You are now programming your multicore! |
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| − | |||
| − | == Where to go from here == |
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| − | |||
| − | There are many good Haskell tutorials and books. Here are some we recommend: |
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| − | |||
| − | '''Tutorials''' |
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| − | * [[Learn_Haskell_in_10_minutes|Haskell in 10 minutes]] |
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| − | * [http://darcs.haskell.org/yaht/yaht.pdf Yet Another Haskell Tutorial] (English) |
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| − | * [http://www.haskell.org/tutorial/ A Gentle Introduction to Haskell] (English, [[Image:GentleFR.pdf|French PDF]]) |
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| − | * [http://learnyouahaskell.com/ Learn You A Haskell For Great Good!] |
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| − | |||
| − | For a complete list of textbooks, references and tutorials: |
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| − | |||
| − | * [[Books and tutorials]] |
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| − | |||
| − | '''Join the community!''' |
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| − | Talk to others in the Haskell community: |
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| − | * [http://haskell.org/mailman/listinfo/haskell-cafe Haskell-Cafe mailing list] |
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| − | * [[IRC channel]] |
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| − | |||
| − | [[Category:Tutorials]] |
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| − | Languages: [[5 adımda Haskell|tur]] [[Cn/Haskell 入门五步走|zh/cn]] [[Tw/Haskell入門的5個步驟|zh/tw]] [[Ja/Haskell入門 5ステップ|ja]] |
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