Convert a string representing a binary number to a base 10 string haskell

Question

I have the string \"1001\" and I want the string \"9\".

The numeric library has the (rather clunky) showIntAtBase, but I haven\'t been able to find the opposite.

Answer 1

From PLEAC:

bin2dec :: String -> Integer
bin2dec = foldr (\c s -> s * 2 + c) 0 . reverse . map c2i
    where c2i c = if c == '0' then 0 else 1