I'm puzzled by the Haskell 98 report, as it doesn't seem to explain
how to desugar top-level pattern declarations, such as
(x,y) = e
In Section 4.4.3 (Function and Pattern Bindings) under Pattern
Bindings it essentially says
``A simple pattern binding has form p = e. The pattern p is matched
"lazily" as an irrefutable pattern, as if there were an implicit ~
in front of it. See the translation in Section 3.12.''
and then goes on the show how to eliminate guards.
In Section 3.12 (Let Expressions) the translation given for
let p = e1 in e0
are
case e1 of ~p -> e0
if no variable in p appears free in e0, and
let p = fix ( \ ~p -> e1) in e0
otherwise.
Both of these translations only work in a expression context and thus
does not work for top level bindings.
It look like the required translation would look a lot like clause (d)
from Figure 3, ie.:
v = e
x1 = case v of p -> x1
...
xn = case v of p -> xn
where v is a new variable and x1,...,xn are the variables bound by p.
Regards,
Tommy
