Am 03.02.2011 17:47, schrieb Aristid Breitkreuz:
I don't see how it follows that there will be lots of repetitions of similar code. Please explain why you think this occurs, and why it is presumably hard to avoid.
Maybe it is no big deal, if you basically use "show" (and even parsing could be done using "show" without many case distinctions). But in "instance Show RequestMethod" of http://hackage.haskell.org/packages/archive/HTTP/4000.1.1/doc/html/src/Netwo... all constructors must be covered and your derived instance is wrong for the "Custom" or "OtherMethod" variant.
In my, possibly naïve, view, you only need to implement methodToByteString once, and methodToString can be implemented as B8.unpack . methodToByteString.
Sure, that's no big deal.
You loose (possibly faster and shorter) pattern matching, but I think it is just as good to use predefined constants and "==" for comparisons.
With my Method type you also get case-insensitivity for free. :-) And it removes the temptation of just writing "PUT" instead of, say, HTTP.methodPut. (You can get non-standard methods with byteStringToMethod, which is a total function.)
Case-insensitive testing is also no big deal. (Write your own equality.) Surely, something like HTTP.methodPut should be used, but (byteStringToMethod "PUT") will also type-check and only give you a run-time error. As an alternative, I've attached my version of request methods just for illustration purposes. The constructor is not exported, therefore you can only create upper-case strings. My methodList is enough to create rqMethodMap or your methodListA. (The data type can be a newtype.) Cheers Christian