[Haskell-cafe] Re: pi

David Benbennick dbenbenn at gmail.com
Wed Oct 10 20:45:57 EDT 2007

On 10/10/07, Dan Weston <westondan at imageworks.com> wrote:
> Actually, it is a constant: piDecimalExpansion :: String.

Where is this constant defined?

> A translation from piDecimalExpansion :: String to pi :: Floating a => a
> is already well defined via read :: Read a => String -> a
> Any definition of pi in the Floating class that differs from (read
> piDecimalExpansion) is erroneous. I propose the above as the default
> definition of pi.

piDecimalExpansion, if defined, would be an infinite length string.
The expression

read $ "0." ++ repeat '1' :: Double

is Bottom.  So even if you had piDecimalExpansion, it isn't clear how
to use that to define pi.

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