connect 4 in Go

connect_four.go

package main

import (
	"fmt"
	"math/rand"
	"os"
	"regexp"
	"strconv"
	"strings"
)

const (
	X = "X"
	Y = "Y"
)

var Xwin = regexp.MustCompile(`XXXX`)
var Ywin = regexp.MustCompile(`YYYY`)

type C4 struct {
	board [6][7]string //The most commonly used Connect Four board size is 7 columns × 6 rows
}

func (c4 *C4) pp() { // pretty print board
	for _, r := range c4.board {
		for _, c := range r {
			fmt.Print(c)
		}
		fmt.Println()
	}
}

func (c4 *C4) play(player string) {
	x, y := rand.Intn(6), rand.Intn(7)
	for c4.board[x][y] != "X" && c4.board[x][y] != "Y" {
		x, y = rand.Intn(6), rand.Intn(7)
		c4.board[x][y] = player
	}
}

func (c4 *C4) horizontalWin() bool {
	for i, r := range c4.board {
		rowState := strings.Join(r[0:6], "")
		if Xwin.MatchString(rowState) {
			fmt.Println("X Won at row:", i+1)
			return true
		}
		if Ywin.MatchString(rowState) {
			fmt.Println("Y Won at row:", i+1)
			return true
		}
	}
	return false
}

func main() {
	c4 := new(C4)
	seedVal := 23
	if len(os.Args) > 1 {
		seedVal, _ = strconv.Atoi(os.Args[1])
	}
	rand.Seed(int64(seedVal)) // pass seed as first arg
	fmt.Println("Initialize Board")
	for i := 0; i < 6; i++ {
		for j := 0; j < 7; j++ {
			c4.board[i][j] = "-"
		}
	}
	c4.pp()
	moves := 0
	for !c4.horizontalWin() {
		moves += 1
		c4.play("Y")
		c4.play("X")
		if moves == 10 { // -- how does the board look after 10 moves
			fmt.Println("Moves:", moves)
			c4.pp()
		}
	}
	fmt.Println("Won after Moves:", moves)
	c4.pp()
}