A small doubt

[Saswat Anand]

Hi,
  I think a lazy pattern is "really lazy" if reference to a part of the
pattern does not
cause matching of rest of the pattern.

For example, 
 \ ~((:) a ((:) b [])) -> [a]
should not try to match ((:) b[]) part of the pattern, since 'a' is only
referenced. 

It seems the above pattern should be interpreted as the following patern:
 \ ~((:) ~a ~((:) ~b ~[])) -> [a]


Prelude>  (\ ~((:) a ((:) b [])) -> [a]) [2]
[
Program error: {v1282 [Num_fromInt instNum_v35 2]}

Prelude>  (\ ~((:) ~a ~((:) ~b ~[])) -> [a]) [2]
[2]      

What are the cons in this interpretation?

Cheers,
Saswat