PROPOSAL: Restrict the type of (^), (^^), and add genericPower,
lemming at henning-thielemann.de
Sat Nov 17 12:33:23 EST 2007
On Sat, 17 Nov 2007, Cale Gibbard wrote:
> On 17/11/2007, Ian Lynagh <igloo at earth.li> wrote:
> > Hi all,
> > This got a warm reception when I mentioned it in
> > http://www.haskell.org/pipermail/haskell-cafe/2007-June/027557.html
> > so I'm formally proposing it now. It's trac #1902:
> > http://hackage.haskell.org/trac/ghc/ticket/1902
> > Note that this is a divergence from Haskell 98 (but the libraries
> > already have a handful of small divergences, and Haskell' is just around
> > the corner...).
> > In my opinion, (^) has the wrong type. Just as we have, for example,
> > (!!) :: [a] -> Int -> a
> > genericIndex :: (Integral b) => [a] -> b -> a
> > we should also have
> > (^) :: (Num a) => a -> Int -> a
> > genericPower :: (Num a, Integral b) => a -> b -> a
> > (or some other function name). The same goes for (^^) (genericPower').
> > In my experience this would remove 99.9% of all defaulting (mostly where
> > you write things like x^12 and 8^12), which means it's easier to get
> > -Wall clean without having to put :: Int annotations everywhere.
> > The impact to GHC's bootlibs and extralibs is minimal. In most cases we
> > have things like 2^15, where Int is clearly fine, although it happens to
> > be defaulted to Integer currently. In Data.Complex we have 2 cases of
> > e^(2::Int) which can now be beautified. There are several cases where
> > the type is inferred to be Int anyway.
> > There are 3 files where we really do have an Integer, and it does
> > matter. They are all for parsing numbers of the form 18e43, in
> > base/Text/Read/Lex.hs, parsec/Text/ParserCombinators/Parsec/Token.hs and
> > haskell-src/Language/Haskell/Lexer.hs.
> > Initial deadline: 1 Dec 2007.
> > Thanks
> > Ian
> This is a move in the opposite direction from what I'd really like to
> see. The Int type is usually a premature optimisation,
Accepted, but then I prefer fixed type 'Integer' as exponent and some
guarantee, that powers with small constant exponents are converted to
products by the optimizer.
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