Re: Proposal: Add hasBitSize to Data.Bits.Bits

On Sun, Jul 29, 2012 at 10:37 AM, Thomas Schilling wrote:

On 29 July 2012 15:37, Thomas DuBuisson wrote:

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Is 'bitSize' a useful function to use monomorphically? It seems a waste and irritating to have it return Maybe if I'm not using Integer.

That is a great point. Most my uses of 'bitSize' are monomorphic and Maybe would just be silly. OTOH, I'd be more than happy to fix up any polymorphic code to include a new BitSize constraint.

To make sure I understand this correctly:

The current problem is that bitSize is a partial function *depending on the type* of its argument (currently it always returns _|_ for Integer, and is total for any other type). That does indeed seem like a Bad Idea.

You propose to:

1. Remove "bitSize" from the Bits class. 2. Add a new class BitSize which only contains the "bitSize" method. Integer would not be an instance of this class.

The downside to this proposal is that the requester (Edward) actually wants a function of type "a -> Maybe Int", so his polymorphic function can handle both infinite bit-types and finite bit-types. With the new class, Edward could write: class BitTraversable i where traverseBits :: <sometype> instance (BitSize i) => BitTraversable i where traverseBits = <something> instance BitTraversable Integer where traverseBits = <something else> Antoine