chore: add Lua scripting example

example/lua-scripting/main.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/go-redis/redis/v8"
+)
+
+func main() {
+	ctx := context.Background()
+
+	rdb := redis.NewClient(&redis.Options{
+		Addr: ":6379",
+	})
+	_ = rdb.FlushDB(ctx).Err()
+
+	fmt.Printf("# INCR BY\n")
+	for _, change := range []int{+1, +5, 0} {
+		num, err := incrBy.Run(ctx, rdb, []string{"my_counter"}, change).Int()
+		if err != nil {
+			panic(err)
+		}
+		fmt.Printf("incr by %d: %d\n", change, num)
+	}
+
+	fmt.Printf("\n# SUM\n")
+	sum, err := sum.Run(ctx, rdb, []string{"my_sum"}, 1, 2, 3).Int()
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("sum is: %d\n", sum)
+}
+
+var incrBy = redis.NewScript(`
+local key = KEYS[1]
+local change = ARGV[1]
+
+local value = redis.call("GET", key)
+if not value then
+  value = 0
+end
+
+value = value + change
+redis.call("SET", key, value)
+
+return value
+`)
+
+var sum = redis.NewScript(`
+local key = KEYS[1]
+
+local sum = redis.call("GET", key)
+if not sum then
+  sum = 0
+end
+
+local num_arg = #ARGV
+for i = 1, num_arg do
+  sum = sum + ARGV[i]
+end
+
+redis.call("SET", key, sum)
+
+return sum
+`)