On 4 Jan 2009, at 07:11, Thomas DuBuisson wrote:
My proposal would be for each selector name to be a special type of
"phantom" type class (existing in the intermediate language only).
This type class would not be accessible by the programmer and thus
s/he couldn't make a polymorphic function for which specialization
would be needed. In other words - in normal circumstances there is
no need for dictionaries and thus no run-time difference between this
method and using different record names.
Example:
data IPv4Hdr = Hdr4 { src, dst :: IPv4 }
data IPv6Hdr = Hdr6 { src, dst :: IPv6 }
At some intermediate stage you'd see:
class Src h s where
src :: h -> s
class Dst h d where
dst :: h -> d
class Src h s | h -> s
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