[Haskell-cafe] Re: Maybe and partial functions

[Neil Mitchell]

Hi

> -- There are no pattern-matching failures here.
> -- The totality is harder to see: all digits are roughly of the same range,
> -- but each recursive call increments base. Eventually, base becomes bigger
> -- than d+9 and so the first alternative will be selected, which is in the
> -- WHNF and so recursion terminates.
> carryPropagate base (C d ds)
>    | carryguess == (d+9) `div` base
>        = C carryguess (C (remainder+nextcarry) fraction)
>    | otherwise
>        = (C (dCorrected `div` base) (C (dCorrected `mod` base) fraction))
>   where carryguess = d `div` base
>         remainder = d `mod` base
>         C nextcarry fraction = carryPropagate (base+1) ds
>         dCorrected = d + nextcarry
>
> e =  map (show.head) $
>      iterate (carryPropagate 2 . map (10*) . tail) $
>      C 2 (rept 1)
>
> en n = "2." ++ concat (take n (tail e))

You still have div and mod, which are partial functions.

Thanks

Neil