Adding formatters for numeric bases

[Icelandjack]

Currently base-16 is the only formatter supported like in text-format — unless there is some reason not to it's easy to define other bases using showIntAtBase from Numeric (similar to Numeric.Lens):

toBase :: (Show a, Integral a) => a -> a -> String
toBase(numBase) n = showIntAtBase numBase intToDigit n ""

base :: (Show a, Integral a) => a -> Format a
base(numBase) = later (T.fromText . T.pack . toBase(numBase))

I made the following as a simple proof of concept, if you're okay with adding it to the project I'll submit a request:

ghci> format (base(2) % " " % base(8) % " " % base(16)) 255 255 255
"11111111 377 ff"
ghci> format (base'(2) % " " % base'(8) % " " % base'(16)) 255 255 255
"0b11111111 0o377 0xff"

with

base'(2)  = "0b" % base(2)
base'(8)  = "0o" % base(8)
base'(16) = "0x" % base(16)
base'(b)  = base(b)

Then specialized bases would be trivially implemented:

bin  = base(2)
bin' = base'(2)
oct  = base(8)
oct' = base'(8)
hex' = base'(16)

As efficiency is concerned, text-format doesn't export integer but a more efficient version for arbitrary bases or specialized for certain base like hexadecimal can be added later.

I'm not sure about the names of the prime functions, if this looks fine I'll add it.

[Icelandjack]

One issue is that showIntAtBase adds Show and Integral constraints while hex only adds Integral.

[chrisdone]

Thoughts:

• I'd prefer to leave hex as it's a fast implementation.
• These other bases are okay as a general base renderer.
• I don't like primes because it doesn't mean anything.
• Don't know what to call the prefixed ones. Maybe prefixBase, if that doesn't defy the point by being longer.
• bin and oct would be consistent with having hex as these three are after all special bases in computing.
• Not too bothered about the Show constraint, it's unfortunate but we can overcome it if it grates later.

I'll definitely accept the base combinator and bin and oct.

[Icelandjack]

Yes I'll leave hex alone and Show doesn't seem to be an issue.