Вот реализация функции факториала на основе цикла "for":

```go
package main

import "fmt"

func factorial(n int) int {
	var factorial = 1

	for i := 1; i <= n; i++ {
		factorial = factorial * i
	}

	return factorial
}

func main() {
	fmt.Println(factorial(5))
}
```
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