To be more specific, there are no statements, everything returns something, including those lines, they just return it ‘up’ (so the if returns it, but the if is not being assigned to anything so it vanishes).

Just to add to the spectrum (i.e. I’m not recommending this) I see Greg’s suggestion as a “cleaned up” version of

a = 20 
b = 10

result = 
  case {a,b} do
    {c,c} -> "equal"
    {c,d} when c > d -> "a"
    {c,d} when c < d -> "b"
  end
reply = {:ok, result}

IO.inspect(reply)

which could also be written as

a = 20 
b = 10

result = 
  case {a,b} do
    _ when a > b -> "a"
    _ when a < b -> "b"
    _ -> "equal"
  end
reply = {:ok, result}

IO.inspect(reply)

leading to the accepted solution

a = 20 
b = 10

result = 
  cond do
    a > b -> "a"
    a < b -> "b"
    true -> "equal"
  end
reply = {:ok, result}

IO.inspect(reply)

And if do always has a “second” value it evaluates to when the condition is false - it will return nil

a = 10 
b = 20

value1 = 
  if a > b do
    "a"  
  end
  
value2 = 
  cond do
    a > b -> "a"
    true -> nil
  end

IO.inspect({value1,value2})

> {nil, nil}

You could use a cond, as shown above, or even different named function heads with pattern matching

def compare(a, a), do: {:ok, “equal”}
def compare(a, b) when a > b, do: {:ok, “a”}
def compare(a, b) when a < b, do: {:ok, “b”}