Export functions on Natural in Numeric.Natural

[Zemyla]

That pretty much sums it up.

On Sun, Mar 22, 2020, 17:55 chessai . <chessai1996 at gmail.com> wrote:

> Sure, I don't see why not. I think powModNatural is also safe.
>
> Are your criteria for a function worth re-exporting from Numeric.Natural
> that
>
> 1. The function does not have an overloaded variant defined in base
> (e.g. all the monorphic version of `fromIntegral` in GHC.Natural would
> be excluded) and
> 2. The function is total?
>
> Thanks
>
> On Sun, Mar 22, 2020 at 11:40 AM Zemyla <zemyla at gmail.com> wrote:
> >
> > Functions in GHC.Natural like naturalToWordMaybe and minusNaturalMaybe
> are extremely useful, especially when trying to write provably total
> functions, and I wish they were available in a Safe module like
> Numeric.Natural. I also want a total function that does the following:
> >
> > -- This function turns an Integer n into a pair of
> > -- (fromInteger (abs n), fromInteger (signum n)).
> > integerToNaturalSign :: Integer -> (Natural, Int)
> > #if 0
> > -- This is the reference version, except for the fact that numeric
> literals don't exist yet
> > -- when GHC.Natural is being defined, and fromInteger isn't actually
> total.
> > integerToNaturalSign n = case compare n 0 of
> >   LT -> (fromInteger (negate n), -1)
> >   EQ -> (0, 0)
> >   GT -> (fromInteger n, 1)
> > #elif !defined(MIN_VERSION_integer_gmp)
> > -- This is like the reference version, except using the newtype wrapper
> and MagicHash.
> > integerToNaturalSign n = case compare n (intToInteger# 0#) of
> >   LT -> (Natural (negateInteger n), I# (-1#))
> >   EQ -> (Natural n, I# 0#)
> >   GT -> (Natural n, I# 1#)
> > #else
> > -- We take advantage of the GMP functions and constructors.
> > integerToNaturalSign (Jn# bn) = (bigNatToNatural bn, I# (-1#))
> > integerToNaturalSign (S# i#) = case isTrue# (i# <# 0#) of
> >   True -> (NatS# (int2Word# (negateInt# i#)), I# (-1#))
> >   _    -> (NatS# (int2Word# i#), I# (i# ># 0#))
> > integerToNaturalSign (Jp# bn) = (bigNatToNatural bn, I# 1#)
> > #endif
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>
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