[Haskell-cafe] Re: Function to cast types

22 Mar 2009

      Achim Schneider  wrote:
...
Anonymous Anonymous  wrote:
...
fromIntToString :: Int -> String
intOfString = sum . map (uncurry (*)) . zip (map (10^) [0..]) 
            . map intOfChar . reverse
/me hides under a stone and tries again, this time with the correct
problem:

import Data.List

charOfInt :: Int -> Char
charOfInt c | c >= 0 && c <= 9 = toEnum (c + fromEnum '0')
charOfInt _ = undefined

stringOfInt :: Int -> String
stringOfInt =
    let f (-1) = Nothing
        f n = let (r,c) = n `divMod` 10
              in Just $ if r == 0 then (c, (-1)) else (c, r)
    in map charOfInt . reverse . unfoldr f

That -1 thing is clearly inelegant, but I don't feel like struggling
with off-by-one errors, right now. Negative numbers are left as an
exercise.

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