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c2b87ce007
I removed the broken function comparison example and fixed a code highlighting regexp. R=golang-dev, adg CC=golang-dev https://golang.org/cl/5501078
106 lines
4.3 KiB
XML
106 lines
4.3 KiB
XML
<codewalk title="First-Class Functions in Go">
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<step title="Introduction" src="doc/codewalk/pig.go">
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Go supports first class functions, higher-order functions, user-defined
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function types, function literals, closures, and multiple return values.
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<br/><br/>
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This rich feature set supports a functional programming style in a strongly
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typed language.
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<br/><br/>
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In this codewalk we will look at a simple program that simulates a dice game
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called <a href="http://en.wikipedia.org/wiki/Pig_(dice)">Pig</a> and evaluates
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basic strategies.
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</step>
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<step title="Game overview" src="doc/codewalk/pig.go:/\/\/ A score/,/thisTurn int\n}/">
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Pig is a two-player game played with a 6-sided die. Each turn, you may roll or stay.
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<ul>
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<li> If you roll a 1, you lose all points for your turn and play passes to
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your opponent. Any other roll adds its value to your turn score. </li>
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<li> If you stay, your turn score is added to your total score, and play passes
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to your opponent. </li>
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</ul>
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The first person to reach 100 total points wins.
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<br/><br/>
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The <code>score</code> type stores the scores of the current and opposing
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players, in addition to the points accumulated during the current turn.
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</step>
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<step title="User-defined function types" src="doc/codewalk/pig.go:/\/\/ An action/,/bool\)/">
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In Go, functions can be passed around just like any other value. A function's
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type signature describes the types of its arguments and return values.
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<br/><br/>
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The <code>action</code> type is a function that takes a <code>score</code>
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and returns the resulting <code>score</code> and whether the current turn is
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over.
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<br/><br/>
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If the turn is over, the <code>player</code> and <code>opponent</code> fields
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in the resulting <code>score</code> should be swapped, as it is now the other player's
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turn.
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</step>
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<step title="Multiple return values" src="doc/codewalk/pig.go:/\/\/ roll returns/,/true\n}/">
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Go functions can return multiple values.
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<br/><br/>
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The functions <code>roll</code> and <code>stay</code> each return a pair of
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values. They also match the <code>action</code> type signature. These
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<code>action</code> functions define the rules of Pig.
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</step>
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<step title="Higher-order functions" src="doc/codewalk/pig.go:/\/\/ A strategy/,/action\n/">
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A function can use other functions as arguments and return values.
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<br/><br/>
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A <code>strategy</code> is a function that takes a <code>score</code> as input
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and returns an <code>action</code> to perform. <br/>
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(Remember, an <code>action</code> is itself a function.)
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</step>
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<step title="Function literals and closures" src="doc/codewalk/pig.go:/return func/,/return roll\n\t}/">
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Anonymous functions can be declared in Go, as in this example. Function
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literals are closures: they inherit the scope of the function in which they
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are declared.
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<br/><br/>
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One basic strategy in Pig is to continue rolling until you have accumulated at
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least k points in a turn, and then stay. The argument <code>k</code> is
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enclosed by this function literal, which matches the <code>strategy</code> type
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signature.
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</step>
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<step title="Simulating games" src="doc/codewalk/pig.go:/\/\/ play/,/currentPlayer\n}/">
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We simulate a game of Pig by calling an <code>action</code> to update the
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<code>score</code> until one player reaches 100 points. Each
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<code>action</code> is selected by calling the <code>strategy</code> function
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associated with the current player.
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</step>
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<step title="Simulating a tournament" src="doc/codewalk/pig.go:/\/\/ roundRobin/,/gamesPerStrategy\n}/">
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The <code>roundRobin</code> function simulates a tournament and tallies wins.
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Each strategy plays each other strategy <code>gamesPerSeries</code> times.
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</step>
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<step title="Variadic function declarations" src="doc/codewalk/pig.go:/\/\/ ratioS/,/string {/">
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Variadic functions like <code>ratioString</code> take a variable number of
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arguments. These arguments are available as a slice inside the function.
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</step>
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<step title="Simulation results" src="doc/codewalk/pig.go:/func main/,/\n}/">
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The <code>main</code> function defines 100 basic strategies, simulates a round
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robin tournament, and then prints the win/loss record of each strategy.
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<br/><br/>
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Among these strategies, staying at 25 is best, but the <a
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href="http://www.google.com/search?q=optimal+play+pig">optimal strategy for
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Pig</a> is much more complex.
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</step>
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</codewalk>
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