选题[tech]: 20201209 Program a simple game with Elixir

sources/tech/20201209 Program a simple game with Elixir.md

sources/tech/20201209 Program a simple game with Elixir.md

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+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+[#]: subject: (Program a simple game with Elixir)
+[#]: via: (https://opensource.com/article/20/12/elixir)
+[#]: author: (Moshe Zadka https://opensource.com/users/moshez)
+
+Program a simple game with Elixir
+======
+Learn Elixir by programming a "guess the number" game and comparing the
+language against ones you know.
+![A die with rainbow color background][1]
+
+To you learn a new programming language, it's good to focus on the things most programming languages have in common:
+
+  * Variables
+  * Expressions
+  * Statements
+
+
+
+These concepts are the basis of most programming languages. Because of these similarities, once you know one programming language, you can start figuring another one out by recognizing its differences.
+
+Another good tool for learning a new language is starting with a standard program. This allows you to focus on the language, not the program's logic. We're doing that in this article series using a "guess the number" program, in which the computer picks a number between one and 100 and asks you to guess it. The program loops until you guess the number correctly.
+
+The "guess the number" program exercises several concepts in programming languages:
+
+  * Variables
+  * Input
+  * Output
+  * Conditional evaluation
+  * Loops
+
+
+
+It's a great practical experiment to learn a new programming language.
+
+### Guess the number in Elixir
+
+The [Elixir][2] programming language is a dynamically typed functional language designed for building stable and maintainable applications. It runs on top of the same virtual machine as [Erlang][3] and shares many of its strengths—but with slightly easier syntax.
+
+You can explore Elixir by writing a version of the "guess the number" game.
+
+Here is my implementation:
+
+
+```
+defmodule Guess do
+  def guess() do
+     random = Enum.random(1..100)
+     IO.puts "Guess a number between 1 and 100"
+     Guess.guess_loop(random)
+  end
+  def guess_loop(num) do
+    data = IO.read(:stdio, :line)
+    {guess, _rest} = Integer.parse(data)
+    cond do
+      guess < num ->
+        IO.puts "Too low!"
+        guess_loop(num)
+      guess > num ->
+        IO.puts "Too high!"
+        guess_loop(num)
+      true ->
+        IO.puts "That's right!"
+    end
+  end
+end
+
+Guess.guess()
+```
+
+To assign a value to a variable, list the variable's name followed by the `=` sign. For example, the statement `random = 0` assigns a zero value to the `random` variable.
+
+The script starts by defining a **module**. In Elixir, only modules can have named functions in them.
+
+The next line defines the function that will serve as the entry point, `guess()`, which:
+
+  * Calls the `Enum.random()` function to get a random integer
+  * Prints the game prompt
+  * Calls the function that will serve as the loop
+
+
+
+The rest of the game logic is implemented in the `guess_loop()` function.
+
+The `guess_loop()` function uses [tail recursion][4] to loop. There are several ways to do looping in Elixir, but using tail recursion is a common one. The last thing `guess_loop()` does is call _itself_.
+
+The first line in `guess_loop()` reads the input from the user. The next line uses `parse()` to convert the input to an integer.
+
+The `cond` statement is Elixir's version of a multi-branch statement. Unlike `if/elif` or `if/elsif` in other languages, Elixir does not treat the first nor the last branch in a different way.
+
+This `cond` statement has a three-way branch: The guess can be smaller, bigger, or equal to the random number. The first two options output the inequality's direction and then tail-call `guess_loop()`, looping back to the beginning. The last option outputs `That's right`, and the function finishes.
+
+### Sample output
+
+Now that you've written your Elixir program, you can run it to play the "guess the number" game. Every time you run the program, Elixir will pick a different random number, and you can guess until you find the correct number:
+
+
+```
+$ elixir guess.exs
+Guess a number between 1 and 100
+50
+Too high
+30
+Too high
+20
+Too high
+10
+Too low
+15
+Too high
+13
+Too low
+14
+That's right!
+```
+
+This "guess the number" game is a great introductory program for learning a new programming language because it exercises several common programming concepts in a pretty straightforward way. By implementing this simple game in different programming languages, you can demonstrate some core concepts of the languages and compare their details.
+
+Do you have a favorite programming language? How would you write the "guess the number" game in it? Follow this article series to see examples of other programming languages that might interest you.
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/20/12/elixir
+
+作者：[Moshe Zadka][a]
+选题：[lujun9972][b]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]: https://opensource.com/users/moshez
+[b]: https://github.com/lujun9972
+[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/dice_tabletop_board_gaming_game.jpg?itok=y93eW7HN (A die with rainbow color background)
+[2]: https://elixir-lang.org/
+[3]: https://www.erlang.org/
+[4]: https://en.wikipedia.org/wiki/Tail_call