For y range en Go

for.go

num := make([]int, 0, tam)
for i, c := range accion {
	if !unicode.IsDigit(c) {
		return nil
	} else if i >= tam {
		return nil
	} else {
		digit := int (c - '0')
		for _, d := range num {
			if digit == d { return nil }
		}
		num = num[0:i+1]
		num[i] = digit
	}
}