PROPOSAL: Restrict the type of (^), (^^), and add genericPower,
genericPower'
Ian Lynagh
igloo at earth.li
Sat Nov 17 09:02:44 EST 2007
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
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