Christian Maeder wrote:
Hi,
I would like haskell to accept the following (currently illegal) expressions as syntactically valid prefix applications:
f = id \ _ -> [] g = id let x = [] in x h = id case [] of [] -> [] i = id do [] j = id if True then [] else []
The rational is that expressions starting with a keyword should extend as far as possible (to the right and over several lines within their layout).
On page 15/16 of the H98 report I think this could be achieved by: exp10 ::= fexp fexp ::= [fexp] keyexp keyexp ::= \ apat ... -> exp | let ... | ... | aexp
(In fact, maybe for haskell' "$" could be changed to a keyword.)
Alternatively the # symbol could be removed from the pool of symbol chars and used to construct syntactic sugar so you could use f = id #$ \_ -> [] to mean exactly f = id (\_ -> []) I think when the idea of $ arose originally people didn't at that time know about the many cases where the use of $ is not semantically equivalent to explict brackets, since this knowledge probably only arose later with the introduction of rank-n polymorphism. (Of course the need for #$ would be fixed with impredicative types as in MLF.) Best regards, Brian.