2008/10/21 John Dorsey
It looks like
"case e' of { y -> ..."
was introduced solely to give e' a name that can be used in two places, since the nested form may fail to match at each level. It seems to me that without this, you could get code explosion from duplicating the expression e' below; with this you get sharing. ...
-- Match v against a constructor with multiple fields case v of { K { f1 = p1 , f2 = p2 , ... } -> e ; _ -> e' }
-- Same, but introduce y to represent e' without loss of sharing case e' of { y -> case v of { K { f1 = p1 , f2 = p2 , ... } -> e ; _ -> y }}
I hope this helps.
Surely it does. Most tricky part here (for me) is that e' goes in outer scope. It works here like in rule (c) . I got it. Thank you for your help. Regards, Michael