On 3/19/06, Manuel M T Chakravarty <[EMAIL PROTECTED]> wrote: > Loosely related to Ticket #76 (Bang Patterns) is the question of whether > we want the language to include strict tuples. It is related to bang > patterns, because its sole motivation is to simplify enforcing > strictness for some computations. Its about empowering the programmer > to choose between laziness and strictness where they deem that necessary > without forcing them to completely re-arrange sub-expressions (as seq > does). > > So what are strict tupples? If a lazy pair is defined in pseudo code as > > data (a, b) = (a, b) > > a strict pair would be defined as > > data (!a, b!) = ( !a, !b ) > > Ie, a strict tuple is enclosed by bang parenthesis (! ... !). The use > of the ! on the rhs are just the already standard strict data type > fields. >
Maybe I've missed something here. But is there really any reasonable usage cases for something like: f !(a,b) = a + b in the current bang patterns proposal? I mean, would anyone really ever want an explicitly strict (i.e. using extra syntax) tuple with lazy elements? Couldn't the syntax for strict tuples be just what I wrote above (instead of adding weird-looking exclamation parenthesis). I'm pretty sure that most programmers who would write "f !(a,b) = ..." would expect the tuple's elements to be forced (they wouldn't expect it to do nothing, at least).. In fact !(x:xs) should mean (intuitively to me, at least) "force x, and xs", meaning that the element x is forced, and the list xs is forced (but not the elements of the xs). Couldn't this be generalised? A pattern match on any constructor with a bang in front of it will force all the parts of the constructor (with seq)? So: f !xs = b -- gives f xs = xs `seq` b, like the current proposal f !(x:xs) = b -- gives f (x:xs) = x `seq` xs `seq` b, unlike the current proposal? The latter would then be equal to f (!x:xs) = b right? Just slightly more convenient in some cases... f (A !b (C !c !d) !e !f !g) = y would be equivalent to: f !(A b !(C c d) e f g) = y Instead of the latter meaning doing nothing... /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862 _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://haskell.org/mailman/listinfo/haskell-prime
