Couldn't '\' delimit a subexpression, as parentheses do? Would there be any ambiguity in accepting code like State \s -> (s, s) instead of requiring State $ \s -> (s, s), or taking
Looking at the Haskell 98 language definition it seems that a whole class of these expressions are disallowed inside function applications:
exp10 -> \ apat1 ... apatn -> exp | let decls in exp | if exp then exp else exp | case exp of { alts } | do { stmts } | fexp
This means that none of the following are legal Haskell declarations, even though they are unambiguous:
a = State \s -> (s, s) b = map let f x = x + 1 in f c = return if a then b else c d = catch do x <- getLine return x
It can be argued that this is mostly obfuscation, and that it can sometimes be confusing, especially with let and do, but it saves on the amount of parentheses or $s. What was the original reasoning for disallowing these more complex expressions as the rightmost argument in an fexp? Or was this simply not considered? Twan