On 09 March 2006 14:40, Simon Marlow wrote:
On 09 March 2006 14:33, Ian Lynagh wrote:
On Wed, Mar 08, 2006 at 10:27:48PM +0100, Doaitse Swierstra wrote:
It is with some hesitation that I want to bring up another point, in which Haskell' could be an improvement above Haskell: the offside rule.
This is something I would have brought up too, except I don't think I'll have time to look into it properly in the advertised timescale.
I conjecture that with a suitable set of bracketing keywords and symbols (if/then, let/in, [/], ...) the "parse error => close implicit block" rule could be dropped without significantly altering the set of acceptable programs (just rejecting programs that people really oughtn't be writing anyway (IMNSHO), like Lennart's examples).
I once conjectured this too, and I even went so far as to measure how many times the parse-error rule was actually used, as opposed to simple bracketting, in all the code I could get my hands on. Conclusion: it was a handful of times in several 10000 LOC, mostly for things like '(case x of p -> e, 42)'.
But ISTR I later discovered a reason that counting brackets wouldn't work so well, but for now it escapes me. I'll try to dig it up.
I remember now: the problem is that 'let' does not always have a matching 'in', e.g. when it is used in 'do', pattern guards or list comprehensions. So you can't consistently treat let/in as brackets. I don't know a way around this. Cheers, Simon