Re: [Haskell-cafe] referential transparency? (for fixity of local operators)
wren ng thornton wren at freegeek.org writes: As for whether the default should be infix 9 instead of infixl 9 ... that was exactly the point of my message. - J. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] referential transparency? (for fixity of local operators)
On 12-10-06 05:18 AM, Johannes Waldmann wrote: wren ng thornton wren at freegeek.org writes: As for whether the default should be infix 9 instead of infixl 9 ... that was exactly the point of my message. - J. Perhaps, half of the people want infixl, another half of the people want infixr, and so at the end the middle ground of neither l nor r is taken. Perhaps, political decision is about saying no to both the left and the right? :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] referential transparency? (for fixity of local operators)
I was really surprised at the following: *Main 1 + 2 * 3 7 *Main ( \ (+) (*) - 1 + 2 * 3 ) (+) (*) 9 because I was somehow assuming that either a) the Prelude fixities of the operators are kept b) or they are undefined, so the parser rejects. but the Haskell standard says Any operator lacking a fixity declaration is assumed to be infixl 9. This really should be infix 9? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] referential transparency? (for fixity of local operators)
* Johannes Waldmann waldm...@imn.htwk-leipzig.de [2012-10-05 11:11:48+] I was really surprised at the following: *Main 1 + 2 * 3 7 *Main ( \ (+) (*) - 1 + 2 * 3 ) (+) (*) 9 because I was somehow assuming that either a) the Prelude fixities of the operators are kept b) or they are undefined, so the parser rejects. but the Haskell standard says Any operator lacking a fixity declaration is assumed to be infixl 9. This really should be infix 9? This behaviour is really handy when you use functions as operators (using backticks notation). They typically lack infix annotations, but having to put parentheses would be very annoying. Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] referential transparency? (for fixity of local operators)
Compile with -Wall and the flaw becomes obvious: interactive:2:5: Warning: This binding for `+' shadows the existing binding imported from `Prelude' (and originally defined in `GHC.Num') interactive:2:9: Warning: This binding for `*' shadows the existing binding imported from `Prelude' (and originally defined in `GHC.Num') interactive:2:16: Warning: Defaulting the following constraint(s) to type `Integer' (Num a0) arising from the literal `1' In the first argument of `(+)', namely `1' In the first argument of `(*)', namely `1 + 2' In the expression: 1 + 2 * 3 interactive:2:16: Warning: Defaulting the following constraint(s) to type `Integer' (Num a0) arising from the literal `1' at interactive:2:16 (Show a0) arising from a use of `print' at interactive:2:1-34 In the first argument of `(+)', namely `1' In the first argument of `(*)', namely `1 + 2' In the expression: 1 + 2 * 3 Shadowing is bad, and tends (as in this case) to be confusing. - Clark On Fri, Oct 5, 2012 at 7:22 AM, Roman Cheplyaka r...@ro-che.info wrote: * Johannes Waldmann waldm...@imn.htwk-leipzig.de [2012-10-05 11:11:48+] I was really surprised at the following: *Main 1 + 2 * 3 7 *Main ( \ (+) (*) - 1 + 2 * 3 ) (+) (*) 9 because I was somehow assuming that either a) the Prelude fixities of the operators are kept b) or they are undefined, so the parser rejects. but the Haskell standard says Any operator lacking a fixity declaration is assumed to be infixl 9. This really should be infix 9? This behaviour is really handy when you use functions as operators (using backticks notation). They typically lack infix annotations, but having to put parentheses would be very annoying. Roman ___ 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
Re: [Haskell-cafe] referential transparency? (for fixity of local operators)
On 10/5/12 7:11 AM, Johannes Waldmann wrote: I was really surprised at the following: *Main 1 + 2 * 3 7 *Main ( \ (+) (*) - 1 + 2 * 3 ) (+) (*) 9 because I was somehow assuming that either a) the Prelude fixities of the operators are kept After dealing with how Coq handles infix operators, I'm profoundly glad that Haskell doesn't do this. The fixity of an operator is a property of the operator itself, not of the notation used to display the operator. There's no reason for my (+) operator to have the same fixity as your (+) operator, regardless of whether we happen to use the same notation or not. b) or they are undefined, so the parser rejects. but the Haskell standard says Any operator lacking a fixity declaration is assumed to be infixl 9. This really should be infix 9? Yep, default fixity. As Roman Cheplyaka mentioned, this is especially helpful for ad hoc uses of backticks. (For non-adhoc uses, it's best to give an explicit fixity just like for other infix operators.) As for whether the default should be infix 9 instead of infixl 9, I dunno... -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
