[racket-dev] #true and #false
[Re-sending; an earlier post of this message seems to be delayed.] What if the default printing format for true and false values in Racket changed from `#t' and `#f' to `#true' and `#false'? The forms `#t', `#T', `#true', `#f', `#F', and `#false' would all be accepted as inputs forms. We could conceivably limit the change to `print' output and not change `write' or `display' output, but let's say for now that the proposal is to change the default for all output modes in Racket. Of course, there would be a parameter to pick the traditional format in any case, and we won't change the printer used for R5RS or R6RS. This proposal originates with the need to fix a problem in the HtDP teaching languages. The HtDP teaching languages currently use `true' and `false' for true and false, and the HtDP languages are configured to print booleans as `true' and `false'. That doesn't work with quoted lists. For example, '(true false) is a list of symbols, not a list of booleans. Using `#t' and `#f' in the teaching languages would avoid the problem, but those forms seem awfully terse. We'd like to try `#true' and `#false', instead. Then, to keep the HtDP and full Racket languages in sync as much as possible, we would like to add `#true' and `#false' to Racket. Along the same lines, consistent printing would be ideal. I'd like to switch to `#true' and `#false' because I often fail to look carefully enough to distinguish `#t' and `#f'. Just this morning, I tried out my prototype reader change in the REPL: Welcome to Racket v5.0.1.7. #true #t #false #t That looked right to me. Of course, new cases in the reader test suite immediately flagged the bug, but I was amused that testing in a REPL didn't make me see the problem in the first place. _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] #true and #false
Sounds great to me, fwiw. Robby On Fri, Oct 8, 2010 at 8:12 PM, Matthew Flatt mfl...@cs.utah.edu wrote: [Re-sending; an earlier post of this message seems to be delayed.] What if the default printing format for true and false values in Racket changed from `#t' and `#f' to `#true' and `#false'? The forms `#t', `#T', `#true', `#f', `#F', and `#false' would all be accepted as inputs forms. We could conceivably limit the change to `print' output and not change `write' or `display' output, but let's say for now that the proposal is to change the default for all output modes in Racket. Of course, there would be a parameter to pick the traditional format in any case, and we won't change the printer used for R5RS or R6RS. This proposal originates with the need to fix a problem in the HtDP teaching languages. The HtDP teaching languages currently use `true' and `false' for true and false, and the HtDP languages are configured to print booleans as `true' and `false'. That doesn't work with quoted lists. For example, '(true false) is a list of symbols, not a list of booleans. Using `#t' and `#f' in the teaching languages would avoid the problem, but those forms seem awfully terse. We'd like to try `#true' and `#false', instead. Then, to keep the HtDP and full Racket languages in sync as much as possible, we would like to add `#true' and `#false' to Racket. Along the same lines, consistent printing would be ideal. I'd like to switch to `#true' and `#false' because I often fail to look carefully enough to distinguish `#t' and `#f'. Just this morning, I tried out my prototype reader change in the REPL: Welcome to Racket v5.0.1.7. #true #t #false #t That looked right to me. Of course, new cases in the reader test suite immediately flagged the bug, but I was amused that testing in a REPL didn't make me see the problem in the first place. _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] #true and #false
Two hours ago, Matthew Flatt wrote: [Re-sending; an earlier post of this message seems to be delayed.] What if the default printing format for true and false values in Racket changed from `#t' and `#f' to `#true' and `#false'? The forms `#t', `#T', `#true', `#f', `#F', and `#false' would all be accepted as inputs forms. We could conceivably limit the change to `print' output and not change `write' or `display' output, but let's say for now that the proposal is to change the default for all output modes in Racket. [...] I'd prefer it if at least `write' keeps it as #t. IMO `write' as a quick way to serialize some data to a file in a way that is also readable is a very big win, and having a single character (in addition to the obligatory # syntax marker) used for booleans makes it fine in most cases, even up to pretty big files. I can see how making it much longer will encourage using some bad home-cooked serializations to avoid the extra size -- and that would be bad. (As for `print' -- seems fine to use the long forms, and I don't have any opinion on `display' (maybe in the name of just show some roughly readable stuff it should use the long forms too).) This proposal originates with the need to fix a problem in the HtDP teaching languages. The HtDP teaching languages currently use `true' and `false' for true and false, and the HtDP languages are configured to print booleans as `true' and `false'. That doesn't work with quoted lists. For example, '(true false) is a list of symbols, not a list of booleans. BTW, wasn't the whole sophisticated quoted printout part of a solution to this, so that those true/false would not print out as quoted? -- ((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay: http://barzilay.org/ Maze is Life! _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] #true and #false
At Fri, 08 Oct 2010 23:10:05 -0400, David Van Horn wrote: On 10/8/10 9:12 PM, Matthew Flatt wrote: This proposal originates with the need to fix a problem in the HtDP teaching languages. The HtDP teaching languages currently use `true' and `false' for true and false, and the HtDP languages are configured to print booleans as `true' and `false'. That doesn't work with quoted lists. For example, '(true false) is a list of symbols, not a list of booleans. What about '(empty)? Seems like the same issue. Yes, so we are also looking at how to move away from `empty'. The answer isn't `#empty' --- at least not without breaking the correspondence between an expression E and `eval' of a `quote'd E. For example, we would want `#empty' by itself to mean the empty list, and quoting `#empty' should also mean the empty list, but `eval'ing the empty list should be an empty application, not the empty list. Maybe we have to use '() for the empty list, even in the teaching languages. _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] #true and #false
Two minutes ago, Matthew Flatt wrote: At Fri, 8 Oct 2010 23:11:21 -0400, Eli Barzilay wrote: BTW, wasn't the whole sophisticated quoted printout part of a solution to this, so that those true/false would not print out as quoted? It's an expression issue, not a printing issue. We tell students that `true' and `false' are literals, and we later tell them that `quote' can be used to form lists of literals, and so they try to write the above. Ah, OK. (Just to mention the other kind of course -- in my class I explicitly make a point about the difference between the common `true'/`false' keywords and racket's identifiers literals. I think that most students still miss that point, and get confused over the quoted identifiers and using them in a `let'.) In any case, this seems to me like it weakens the case for the longer names being used globally rather than only in the teaching languages. (But I'm still not objecting, except for the same `write' point I made.) -- ((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay: http://barzilay.org/ Maze is Life! _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
