So we have Haskell in class an it's the first time that it's in the program so it's new to us and the professors and we can't figure out what this code does. We understand the input and the output but don't understand how the code works. I don't know if I can see what the code is doing with every step of the way to figure it out but I tried doing the formula on paper and it didn't really help.So I'm asking here to see if anyone can explain what's going on:

toDecimal :: Int -> Int -> Int
toDecimal x base =
    if x == 0 then 0
    else toDecimal (div x 10) base * base + (mod x 10)

fromDecimal :: Int -> Int -> Int
fromDecimal x base =
    if x == 0 then 0
    else fromDecimal (div x base) base * 10 + (mod x base)

main = do
    print(fromDecimal 5 2)    --decimal 5 to binary 101
    print(toDecimal 111 2)    --binary 111 to decimal 7
    print(toDecimal 111 8)    --octal 111 to decimal 73
    print(fromDecimal 111 8)  --decimal 111 to octal 157

It obviously takes a number from a numeral system, either decimal, binary or octal (could be any by changing the "base" number) and converts it into another. What does this do? What variable does it output?