On Sat, Nov 30, 2013 at 5:40 PM, Patrick Browne
I am trying to write my own simplified class and instances for equality. I have trouble with the equality equation for the empty list. Even though I can use the [] == [] at the GHCi prompt I cannot use it in my equality test. How can I make my eq test handle empty lists while staying within the context of my current code?.
You can't unless you include an Eq constraint on a, since Eq is what "defines" (==). In your other instance, you use Int and Int has an Eq instance. ghci can do it because of extended defaulting: it uses () for a, and there is an Eq instance for (). But this would not help you in an instance definition. -- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net