Wouldn't it be judicious to warn the user whenever a variable appears in
the left hand-side of a (let/pattern-) binding and not used anymore in
the following code, like they do in Prolog (e.g. within the Eclipse
compiler) ? This is one of the source of many (of my) stupid bugs
(especially when modifying pieces of code) and surely a desirable
feature of a correct program. It seems also not
so intricate to check (from my naive user standpoint at least).

Cheers

-- Nicolas