Marcin 'Qrczak' Kowalczyk [EMAIL PROTECTED] said:
The side effect of using data with a strict argument
instead of
newtype is that
f' (C2 x) (C2 y) = C2 (f x y)
unexpectedly becomes strict in both arguments, and we
would have
to write
f' x y = C2 (f (case x of C2 x' -> x')
(case y of C2 y' -> y'))
in the general case where we want to preserve strictness
and don't
want to analyze it ourselves. Newtypes allow to use the
convenient
syntax of pattern matching on the lhs.
---------
Surely you could just write
f' ~(C2 x) ~(C2 y) = C2 (f x y)
which makes the laziness explicit. Since you have to
modify the pattern anyway when changing from a type to a
newtype/datatyp., it would seem that the added documentary
value of the explicit lazy patterns is worth the extra
work....
David Feuer
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