What I always do is to write it like this:
equal pair@Pair{} = foo pair == bar pair
The {} syntax ensures that it doesn't matter how complex the Pair constructor is.
Sjoerd
On Jul 18, 2013, at 1:52 PM, harry
All of the proposed solutions seem to rely on pattern matching in the constructor, which isn't always feasible. Here's a slightly better example:
data Pair a = (Num a, Eq a) => Pair {x::a,y::a}
equal :: Pair a -> Bool equal pair = (foo pair) == (bar pair)
foo pair = (x pair) * (y pair)
bar pair = (y pair) + (x pair)
Now imagine that foo and bar are part of a library which I don't control, or that for some other reason I can't just change foo and bar to take only the components of Pair (e.g. it's a complex type with numerous components and subcomponents).
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