1 <codewalk title="First-Class Functions in Go"> 2 3 <step title="Introduction" src="doc/codewalk/pig.go"> 4 Go supports first class functions, higher-order functions, user-defined 5 function types, function literals, closures, and multiple return values. 6 <br/><br/> 7 8 This rich feature set supports a functional programming style in a strongly 9 typed language. 10 <br/><br/> 11 12 In this codewalk we will look at a simple program that simulates a dice game 13 called <a href="http://en.wikipedia.org/wiki/Pig_(dice)">Pig</a> and evaluates 14 basic strategies. 15 </step> 16 17 <step title="Game overview" src="doc/codewalk/pig.go:/\/\/ A score/,/thisTurn int\n}/"> 18 Pig is a two-player game played with a 6-sided die. Each turn, you may roll or stay. 19 <ul> 20 <li> If you roll a 1, you lose all points for your turn and play passes to 21 your opponent. Any other roll adds its value to your turn score. </li> 22 <li> If you stay, your turn score is added to your total score, and play passes 23 to your opponent. </li> 24 </ul> 25 26 The first person to reach 100 total points wins. 27 <br/><br/> 28 29 The <code>score</code> type stores the scores of the current and opposing 30 players, in addition to the points accumulated during the current turn. 31 </step> 32 33 <step title="User-defined function types" src="doc/codewalk/pig.go:/\/\/ An action/,/bool\)/"> 34 In Go, functions can be passed around just like any other value. A function's 35 type signature describes the types of its arguments and return values. 36 <br/><br/> 37 38 The <code>action</code> type is a function that takes a <code>score</code> 39 and returns the resulting <code>score</code> and whether the current turn is 40 over. 41 <br/><br/> 42 43 If the turn is over, the <code>player</code> and <code>opponent</code> fields 44 in the resulting <code>score</code> should be swapped, as it is now the other player's 45 turn. 46 </step> 47 48 <step title="Multiple return values" src="doc/codewalk/pig.go:/\/\/ roll returns/,/true\n}/"> 49 Go functions can return multiple values. 50 <br/><br/> 51 52 The functions <code>roll</code> and <code>stay</code> each return a pair of 53 values. They also match the <code>action</code> type signature. These 54 <code>action</code> functions define the rules of Pig. 55 </step> 56 57 <step title="Higher-order functions" src="doc/codewalk/pig.go:/\/\/ A strategy/,/action\n/"> 58 A function can use other functions as arguments and return values. 59 <br/><br/> 60 61 A <code>strategy</code> is a function that takes a <code>score</code> as input 62 and returns an <code>action</code> to perform. <br/> 63 (Remember, an <code>action</code> is itself a function.) 64 </step> 65 66 <step title="Function literals and closures" src="doc/codewalk/pig.go:/return func/,/return roll\n\t}/"> 67 Anonymous functions can be declared in Go, as in this example. Function 68 literals are closures: they inherit the scope of the function in which they 69 are declared. 70 <br/><br/> 71 72 One basic strategy in Pig is to continue rolling until you have accumulated at 73 least k points in a turn, and then stay. The argument <code>k</code> is 74 enclosed by this function literal, which matches the <code>strategy</code> type 75 signature. 76 </step> 77 78 <step title="Simulating games" src="doc/codewalk/pig.go:/\/\/ play/,/currentPlayer\n}/"> 79 We simulate a game of Pig by calling an <code>action</code> to update the 80 <code>score</code> until one player reaches 100 points. Each 81 <code>action</code> is selected by calling the <code>strategy</code> function 82 associated with the current player. 83 </step> 84 85 <step title="Simulating a tournament" src="doc/codewalk/pig.go:/\/\/ roundRobin/,/gamesPerStrategy\n}/"> 86 The <code>roundRobin</code> function simulates a tournament and tallies wins. 87 Each strategy plays each other strategy <code>gamesPerSeries</code> times. 88 </step> 89 90 <step title="Variadic function declarations" src="doc/codewalk/pig.go:/\/\/ ratioS/,/string {/"> 91 Variadic functions like <code>ratioString</code> take a variable number of 92 arguments. These arguments are available as a slice inside the function. 93 </step> 94 95 <step title="Simulation results" src="doc/codewalk/pig.go:/func main/,/\n}/"> 96 The <code>main</code> function defines 100 basic strategies, simulates a round 97 robin tournament, and then prints the win/loss record of each strategy. 98 <br/><br/> 99 100 Among these strategies, staying at 25 is best, but the <a 101 href="http://www.google.com/search?q=optimal+play+pig">optimal strategy for 102 Pig</a> is much more complex. 103 </step> 104 105 </codewalk> 106
