TicTacToe in Go

package main

import (
    "bufio"
    "fmt"
    "math/rand"
    "os"
    "strconv"
)

func main() {
    reader := bufio.NewReader(os.Stdin)

    players := [...]string{"X", "O"}
    moveNumber := 0
    grid := [...]string{"1", "2", "3", "4", "5", "6", "7", "8", "9"}

    showGrid := func() {
        fmt.Printf("%s %s %s\n", grid[0], grid[1], grid[2])
        fmt.Printf("%s %s %s\n", grid[3], grid[4], grid[5])
        fmt.Printf("%s %s %s\n", grid[6], grid[7], grid[8])
    }

    showMenu := func() {
        fmt.Println("Tic Tac Toe")
        fmt.Println("1. Versus")
        fmt.Println("2. Computer Versus")
        fmt.Println("3. Exit")
    }

    gameState := func() string {
        if grid[0] == grid[1] && grid[2] == grid[0] || grid[3] == grid[4] && grid[5] == grid[3] ||
            grid[6] == grid[7] && grid[8] == grid[6] || grid[0] == grid[3] && grid[6] == grid[0] ||
            grid[1] == grid[4] && grid[7] == grid[1] || grid[2] == grid[5] && grid[8] == grid[2] ||
            grid[0] == grid[4] && grid[8] == grid[0] || grid[2] == grid[4] && grid[6] == grid[2] {
            return "win"
        } else if moveNumber == 9 {
            return "draw"
        }
        return "still playing"
    }

    versus := func() {
        for {
            showGrid()

            currentPlayer := players[moveNumber%2]

            line, _, _ := reader.ReadLine()
            choice, err := strconv.ParseInt(string(line), 10, 64)
            wrongRange := choice < 1 || choice > 9

            for ; err != nil || wrongRange; {
                fmt.Println("Wrong input")

                line, _, _ = reader.ReadLine()
                choice, err = strconv.ParseInt(string(line), 10, 64)
                wrongRange = choice < 1 || choice > 9
            }

            grid[choice-1] = currentPlayer

            moveNumber++
            fmt.Println()

            switch gameState() {
            case "win":
                showGrid()
                fmt.Println(currentPlayer + " won")
                return
            case "draw":
                showGrid()
                fmt.Println("It's a draw")
                return
            }
        }
    }

    computer := func() {
        for {
            showGrid()

            currentPlayer := players[moveNumber%2]
            if currentPlayer == "X" {
                line, _, _ := reader.ReadLine()
                choice, err := strconv.ParseInt(string(line), 10, 64)
                wrongRange := choice < 1 || choice > 9

                for ; err != nil || wrongRange; {
                    fmt.Println("Wrong input")

                    line, _, _ = reader.ReadLine()
                    choice, err = strconv.ParseInt(string(line), 10, 64)
                    wrongRange = choice < 1 || choice > 9
                }

                grid[choice-1] = "X"
            } else {
                var choice int
                if grid[0] == grid[1] && grid[2] != "X" && grid[2] != "O" {
                    choice = 2
                } else if grid[1] == grid[2] && grid[0] != "X" && grid[0] != "O" {
                    choice = 0
                } else if grid[0] == grid[2] && grid[1] != "X" && grid[1] != "O" {
                    choice = 1

                } else if grid[3] == grid[4] && grid[5] != "X" && grid[5] != "O" {
                    choice = 5
                } else if grid[4] == grid[5] && grid[3] != "X" && grid[3] != "O" {
                    choice = 3
                } else if grid[3] == grid[5] && grid[4] != "X" && grid[4] != "O" {
                    choice = 4

                } else if grid[6] == grid[7] && grid[8] != "X" && grid[8] != "O" {
                    choice = 8
                } else if grid[7] == grid[8] && grid[6] != "X" && grid[6] != "O" {
                    choice = 6
                } else if grid[6] == grid[8] && grid[7] != "X" && grid[7] != "O" {
                    choice = 7

                } else if grid[0] == grid[3] && grid[6] != "X" && grid[6] != "O" {
                    choice = 6
                } else if grid[3] == grid[6] && grid[0] != "X" && grid[0] != "O" {
                    choice = 0
                } else if grid[0] == grid[6] && grid[3] != "X" && grid[3] != "O" {
                    choice = 3

                } else if grid[1] == grid[4] && grid[7] != "X" && grid[7] != "O" {
                    choice = 7
                } else if grid[4] == grid[7] && grid[1] != "X" && grid[1] != "O" {
                    choice = 1
                } else if grid[1] == grid[7] && grid[4] != "X" && grid[4] != "O" {
                    choice = 4

                } else if grid[2] == grid[5] && grid[8] != "X" && grid[8] != "O" {
                    choice = 8
                } else if grid[5] == grid[8] && grid[2] != "X" && grid[2] != "O" {
                    choice = 2
                } else if grid[2] == grid[8] && grid[5] != "X" && grid[5] != "O" {
                    choice = 5

                } else if grid[0] == grid[4] && grid[8] != "X" && grid[8] != "O" {
                    choice = 8
                } else if grid[4] == grid[8] && grid[0] != "X" && grid[0] != "O" {
                    choice = 0
                } else if grid[0] == grid[8] && grid[4] != "X" && grid[4] != "O" {
                    choice = 4

                } else if grid[2] == grid[4] && grid[6] != "X" && grid[6] != "O" {
                    choice = 6
                } else if grid[4] == grid[6] && grid[2] != "X" && grid[2] != "O" {
                    choice = 2
                } else if grid[2] == grid[6] && grid[4] != "X" && grid[4] != "O" {
                    choice = 4

                } else {
                    choice = rand.Intn(9)
                    for ; grid[choice] == "O" || grid[choice] == "X"; {
                        choice = rand.Intn(9)
                    }
                }

                grid[choice] = "O"
            }

            moveNumber++
            fmt.Println()

            switch gameState() {
            case "win":
                showGrid()
                fmt.Println(currentPlayer + " won")
                return
            case "draw":
                showGrid()
                fmt.Println("It's a draw")
                return
            }
        }

        showGrid()
        fmt.Println(players[(moveNumber-1)%2] + " won")
        fmt.Println()
    }

    for {
        showMenu()

        line, _, _ := reader.ReadLine()
        choice, err := strconv.ParseInt(string(line), 10, 64)
        wrongRange := choice < 1 || choice > 3

        for ; err != nil || wrongRange; {
            fmt.Println("Wrong input")

            line, _, _ = reader.ReadLine()
            choice, err = strconv.ParseInt(string(line), 10, 64)
            wrongRange = choice < 1 || choice > 3
        }

        fmt.Println()

        switch choice {
        case 1:
            versus()
        case 2:
            computer()
        case 3:
            return
        }

        fmt.Println()

        moveNumber = 0
        grid = [...]string{"1", "2", "3", "4", "5", "6", "7", "8", "9"}
    }
}