2008/10/2 John Dorsey <[EMAIL PROTECTED]>: > All, > > I'm bundling responses to save paper. > > [EMAIL PROTECTED] wrote: >> I hope it has a Monad instance. > > Naturally! > >> But more to the point: Can it send email? > > Can you give an example of a use case? Do the Haskell-98 standard > tuples have a correspondence feature? I wasn't able to find one with > Hoogle. > > Simon Brenner wrote: >> You could always use this one-tuple instead and get Functor, Monad and >> MonadFix for free: > > As Luke pointed out, that one seems to be too strict. It may simplify > the strict implementation, though. The initial release did have Monad > and Functor instances... I'll look into MonadFix (thanks!). > > Luke Palmer wrote: >> Hmm, it looks like you forgot to write a Traversable instance. > > Oops... I included the instance statement but retained the default, > mutually recursive methods. Too bad GHC didn't warn me. (Pesky > halting problem.) Your change is in 0.1.1 -- thanks! > > Benjamin L.Russell wrote: >> Wonderful! I'm intrigued.... > > Thank you. > >> What is the syntax for the singleton tuple? [...] What is your >> solution? > > Haskell has no such syntax, of course. '(x)' is no good due to > ambiguity with parens' usual associative use. '(x,)' has been > discussed, I think. It's ugly; it's inconsistent with other tuples, > which don't share its final comma; it looks a bit like a tuple section, > which could cause confusion. > > My solution was to use a normal Algebraic Data Type: > data OneTuple a = OneTuple a > > I think the need for singleton tuples is rare enough that the > syntactic inconsistency is tolerable. > > Jon Fairbairn suggests using unicode 0x27e8 and 0x27e0 in place of > parentheses for tuples. I like the idea, especially as an alternate > syntax for the same tuple types, permitting the singleton. > > minh thu writes: >> I thought to this idea in another way : parenthesis could be used for >> s-expressions and [unicode 0x27e8 and 0x27e0] could be used for >> regular grouping. This would allow to switch in the same code between >> infix and s-expr (e.g. enabling SXML)... > > I don't think I fully understand your proposal, although it sounds > interesting. >
(It's not related to your tuple) Here is an example, quite contrived: With angle bracket: f a b c d = a + (+ b ⟨c + d⟩) -- the + before the b is in prefix position is equivalent to Normal Haskell: f a b c d = a + (b + (c + d)) With angle brackets, parenthesis mean "this is an s-expr" and angle brackets mean "this is an standard (infix) expression". In the s-expr, there is no precedence rules while they are kept in the top level or in angle brackets. Hope it's clearer, Thu
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