Re: [Haskell-cafe] Re: Automatic fixity allocation for symbolic operators
On Mon, 16 Oct 2006, Jón Fairbairn [EMAIL PROTECTED] wrote: I made a more concrete proposal later and Phil Wadler tidied it up. I think It even got as far as a draft of the language, [...] Do you know where this proposal/draft can be found? -- /NAD ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Automatic fixity allocation for symbolic operators
Nils Anders Danielsson [EMAIL PROTECTED] writes: On Mon, 16 Oct 2006, Jón Fairbairn [EMAIL PROTECTED] wrote: I made a more concrete proposal later and Phil Wadler tidied it up. I think It even got as far as a draft of the language, [...] Do you know where this proposal/draft can be found? On the fplangc mailing list. Thomas Johnsson has the archive, but as it was a closed mailing list I don't know if it's OK to publish the URL. -- Jón Fairbairn [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Automatic fixity allocation for symbolic operators
Nicolas Frisby wrote: What if operator precedences were specified as a partial order instead of using numbers? Henning Thielemann wrote: dict.leo.org says: great minds think alike Funny, I thought of this too. It seems very natural. You would probably want an implicit taking of transitive closure, to reduce the needed number of declarations. However, to consistently parse an expression, the precedence relation does not need to be transitive (right? one only needs to compare the precedence of adjacent operators), so you could even allow cycles in the precedence graph :s - not sure if that would ever be useful. Perhaps Brian's original idea of systematically determining unspecified operator precedences could be recast in this system. Consider (woefully under contemplated) precedence specifiers such as: precInherit * - @*@ precAll ?+? ?*? Regarding precAll: I'm not a regular expressions/glob for semantics fan, but you get the idea. I'm not convinced that it would be helpful to attach some special meaning to the layout of the operator symbol. -- Mr. Pelican Shit may be Willy. ^ /e\ --- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Automatic fixity allocation for symbolic operators
Nicolas Frisby [EMAIL PROTECTED] writes: What if operator precedences were specified as a partial order instead of using numbers? I suggested something that did that to fplangc back in 1987... Thu, 19 Nov 87 17:49:50 GMT in fact! Simon PJ later forwarded a message from Stef Joosten to similar effect... I made a more concrete proposal later and Phil Wadler tidied it up. I think It even got as far as a draft of the language, but I think it was decided that it was just too difficult (both for human and computer) to parse. -- Jón Fairbairn [EMAIL PROTECTED] http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2006-09-13) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Automatic fixity allocation for symbolic operators
Good evening, Bulat Ziganshin wrote: but when you want to have user-defined operators, that will mean that you need either to define precedences to all other operators (including those from other libs), or sometimes user programs will not compile because they used combination of operators with undefined precedence good for making good headache :) Why is that? A library would indeed only declare the relative precedence of its operators with respect to operators that 1) it knows of; and 2) are related (or general) enough so that there is a reasonable choice of precedence. I think it is even good to force the user to declare any other, more uncommon, precedences; better than the current situation, where the relative precedence of operators from unrelated libraries is fixed pretty much arbitrarily, as an artefact of the imposed total order. Regards, Arie -- Mr. Pelican Shit may be Willy. ^ /e\ --- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Automatic fixity allocation for symbolic operators
I would imagine (reading into Jon Fairbairn's note) that the difficulty is in combining it with the traditional handling of precedences in parsing systems, as Bulat was describing. AFAIK, which is not much on this topic, the notion of precedence in traditional LR spewers is strictly tied to numeric precedences that are known pretty much a priori. Since mapping all the way to numbers seems like overkill to resolve such infix ambiguities, I'd expect such an adjustment to parser generators wouldn't be horrific--it may even be more natural on the implementation side. Nick On 10/16/06, Arie Peterson [EMAIL PROTECTED] wrote: Good evening, Bulat Ziganshin wrote: but when you want to have user-defined operators, that will mean that you need either to define precedences to all other operators (including those from other libs), or sometimes user programs will not compile because they used combination of operators with undefined precedence good for making good headache :) Why is that? A library would indeed only declare the relative precedence of its operators with respect to operators that 1) it knows of; and 2) are related (or general) enough so that there is a reasonable choice of precedence. I think it is even good to force the user to declare any other, more uncommon, precedences; better than the current situation, where the relative precedence of operators from unrelated libraries is fixed pretty much arbitrarily, as an artefact of the imposed total order. Regards, Arie -- Mr. Pelican Shit may be Willy. ^ /e\ --- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
