Re: [Haskell-cafe] Layout rule (was Re: PrefixMap: code review request)
On 28/02/06, Brian Hulley <[EMAIL PROTECTED]> wrote: > > Why? Surely typing one tab is better than having to hit the spacebar 4 (or > 8) times? > > I'm really puzled here. I've been using tabs to indent my C++ code for at > least 10 years and don't see the problem. The only problem would be if > someone mixed tabs with spaces. Since it has to be either tabs only or > spaces only I'd choose tabs only to save keystrokes. I suppose though it is > always going to be a matter of personal taste... > It's easy to configure most editors (vim and emacs included of course) to treat multiple spaces as if they were tabs, but to only save spaces into your file. This is what I do, as it ensures that the way that the code looks to me in my editor is exactly what it looks like to the compiler. Quite often, if it looks better, I will align things past a tab stop with a few extra spaces (which only has to be done once, if your editor will start the next line at the same indentation as the previous). - Cale ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Layout rule (was Re: PrefixMap: code review request)
Am Mittwoch, 1. März 2006 11:57 schrieb Benjamin Franksen: > TAB characters in program text should be forbidden by law. As well as > editors that by default insert a tab char instead of spaces. > As founding member of the church of "The only good Tabbing involves Michaela", I wholeheartedly agree. Cheers, Daniel -- "In My Egotistical Opinion, most people's C programs should be indented six feet downward and covered with dirt." -- Blair P. Houghton ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Layout rule (was Re: PrefixMap: code review request)
On Wednesday 01 March 2006 02:36, Brian Hulley wrote: > Ben Rudiak-Gould wrote: > > Brian Hulley wrote: > >> Here is my proposed layout rule: > >> > >> 1) All layout keywords (where, of, let, do) must either be > >> followed by a single element of the corresponding block type, and > >> explicit block introduced by '{', or a layout block whose first > >> line starts on the *next* line > > > > I wouldn't have much trouble adapting to that. > > > >> and whose indentation is accomplished *only* by tabs > > > > You can't be serious. This would cause far more problems than the > > current rule. > > Why? Surely typing one tab is better than having to hit the spacebar > 4 (or 8) times? What kind of editor are you using? Notepad? I am used to hitting TAB key and get the correct number of spaces, according to how I configured my editor (NEdit) for the current language mode. TAB characters in program text should be forbidden by law. As well as editors that by default insert a tab char instead of spaces. Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Layout rule (was Re: PrefixMap: code review request)
On Wed, 2006-03-01 at 01:36 +, Brian Hulley wrote: > Currently all the ASCII editors I know of only do keyword highlighting, or > occasional ("wait a second while I'm updating the buffer") identifier > highlighting. hIDE and Visual Haskell use the ghc lexer and get near-instantaneous syntax highlighting. Because they use a proper lexer they get fully accurate highlighting, not your ordinary "fairly close" regex-based highlighting. They also only re-lex the bits needed. They keep the lexer state for the start of each line and when a line changes, start re-lexing from the beginning of that line and keep going until the lexer ends up in the same state as a previously saved state on a line. I may be wrong but I think there is an optimisation to not lex beyond the end of the current screen until it is scrolled. This means that even when someone types "{-"m you never have to re-lex & re-highlight more than a screen full. > What I'm trying to get however is complete grammatical > highlighting and type checking that is instantaneous as the user types code, > so this means that the highlighter/type checker needs a complete AST (with > 'gap' nodes to represent spans of incomplete/bad syntax) to work from. With hIDE and Visual Haskell we have found it sufficient to do a complete parse rather than do it incrementally. We wait for a second or so after the user has stopped typing (since highlighting errors as you're actually typing would just be annoying) and then run the ghc front end. This is sufficiently fast (except perhaps on very large modules). > However it is way too expensive to re-parse the whole of a big buffer after > every keypress (I tried it with a parser written in C++ to parse a variant > of ML and even with the optimized build and as many algorithmic > optimizations as I could think of it was just far too slow, and I wasn't > even trying to highlight duplicate identifiers or do type inference) It may be possible to do some more caching to speed things up without going to a full incremental parser. For example the editor could maintain a buffer of lexed symbols and have a traditional parser use that. It may also be possible to just re-parse parts of the file. > Thus to get a fast responsive editing environment which needs to maintain a > parse of the whole buffer to provide effective grammatical highlighting and > not just trivial keyword highlighting it seems (to me) to be essential to be > able to limit the effect of any keystroke especially when the user is just > typing text from left to right but where there may be more stuff after the > cursor eg if the user has gone back to editing a function at the top of a > file. Things like {- would mean that all the parse trees for everything > after it would have to be discarded. Also, flashing of highlighting on this > scale could be very annoying for a user, so I'd rather just delete this > particular possibility of the user getting annoyed when using my software > :-) thus my hopeless attempts to convince everyone that {- is bad news all > round :-))) As I mentioned, it is possible to limit the effect of a {- to a screen full of re-lexing. I grant you that it's likely to do worse things to your incremental parser. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Layout rule (was Re: PrefixMap: code review request)
BH> > Why? Surely typing one tab is better than having to hit the spacebar 4 (or 8) BH> > times? PC> Not when it prevents me from ever exhibiting the slightest shred of style PC> in my code. I use that control for readability purposes in my code. > [snip] BH> I'm really puzled here. I've been using tabs to indent my C++ code for at BH> least 10 years and don't see the problem. At least two reasons: 1. C++ doesn't care about any whitespace (except to separate tokens). Haskell cares about leading whitespace (which it is clear you are thinking a lot about...) but 2. as Philippa mentioned, Haskell programmers care a ton about inter-line, inter-word layout/alignment, for example, lining up = signs and arguments to functions in pattern matches, etc. C++ does not invite this style of declarative programming so it is not surprising that it wasn't an issue: aside from the indentation, I rarely type fancy whitespace inside a giving line of C++ code to align elements with those on a preceding line. In Haskell, this unofficial layout "style" doesn't affect the machine-parsing of the code, but rather the human-parsing of the code. (In fact, it's one of my favorite things about Haskell.) If you want to see what can be accomplished with variable width fonts and complex layouts (not just beginning of lines but rather inter-line, inter-word alignment) you should checkout lhs2TeX. They accomplish all their magic with spaces. BH> The only problem would be if BH> someone mixed tabs with spaces. Since it has to be either tabs only or BH> spaces only I'd choose tabs only to save keystrokes. BTW, tab doesn't type the tab character (at least in emacs and I think vim) but instead moves the left edge of the current line by adding or deleted spaces (or trying to ident the right amount). This usually means you don't have to type 4 or 8 spaces. (And anyway, I would just hold the key down if I had to type more than one spacebar, etc.) > [snip] > For example on Windows Trebuchet MS is a very nice font, also Verdana, both > of which are not monospaced. But yes I agree it's not a major issue and I > just see the option of being able to use them as a nice side-effect. Very few programmers I know would go to variable width fonts just to use some Microsoft font to edit code... (BTW I like Trebuchet and Verdana too.) To each his/her own! Cheers, Jared. -- http://www.updike.org/~jared/ reverse ")-:" ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Layout rule (was Re: PrefixMap: code review request)
On Wed, 1 Mar 2006, Brian Hulley wrote: > Ben Rudiak-Gould wrote: > > Brian Hulley wrote: > > > Here is my proposed layout rule: > > > > > > and whose indentation is accomplished *only* by tabs > > > > You can't be serious. This would cause far more problems than the > > current rule. > > Why? Surely typing one tab is better than having to hit the spacebar 4 (or 8) > times? > Not when it prevents me from ever exhibiting the slightest shred of style in my code. I use that control for readability purposes in my code. -- [EMAIL PROTECTED] "My religion says so" explains your beliefs. But it doesn't explain why I should hold them as well, let alone be restricted by them. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Layout rule (was Re: PrefixMap: code review request)
Ben Rudiak-Gould wrote: Brian Hulley wrote: Here is my proposed layout rule: 1) All layout keywords (where, of, let, do) must either be followed by a single element of the corresponding block type, and explicit block introduced by '{', or a layout block whose first line starts on the *next* line I wouldn't have much trouble adapting to that. and whose indentation is accomplished *only* by tabs You can't be serious. This would cause far more problems than the current rule. Why? Surely typing one tab is better than having to hit the spacebar 4 (or 8) times? I would also make it that explicit braces are not allowed to switch off the layout rule (ie they can be used within a layout), I don't understand. What does "used within a layout" mean? I meant that {;} would be used just like any other construct that has to respect the layout rule so you could write let a = let { b = 6; z = 77; h = 99; p = 100} in b+z+h + p etc but not: let a = let { b = 6; z = 77; h = 99; -- this binding would be part of the outermost 'let' p = 100} in b+z+h + p multiline strings would not be permitted, They aren't now, except with \ escapes. A stray " will be caught on the same line unless the line happens to end with \ and the next line happens to begin with \, which is exceedingly unusual. and multiline comments would not be permitted (pragmas could easily be used just by using --#) But --# doesn't introduce a comment. And this would make UNPACK pragmas rather inconvenient to use. -- # but I hadn't thought about UNPACK... The motivation in both points is to make it easy for an editor to determine which lines need to be re-parsed based on the number of leading tabs alone. 1) When you see a ';' you could immediately tell which block it belongs to by looking backwards till the next '{' I guess that might be helpful, but it doesn't seem easier than looking left to the beginning of the current line and then up to the first less-indented line. There was an example posted on another thread where someone had got into confusion by using ; after a let binding in a do construct with an explicit brace after the 'do' but not after the 'let' (sorry I can't find it again). Also the current layout rule uses the notion of an implicit opening brace which is a to be regarded as a real opening brace as far as ';' in concerned but an unreal non-existent opening brace as far as '}' is concerned. Thus I think it is a real mix-up. 2) Variable width fonts can be used, They can be used now, if you adhere to a certain style, but not everyone likes that style. I wrote in C++ with a variable width font and tabs at one time, but eventually went back to fixed width. One reason was that I couldn't use comment layout conventions that tend (in my experience) to improve readability more than monospacing hurts it. Another reason was that glyph widths appropriate to natural languages didn't work all that well for source code. Spaces are much more important in source code than in natural language, for example. A proportional font designed for source code would be nice, but I haven't found one yet. Stroustrup used a mixture of proportional and monospaced glyphs in _The C++ Programming Language_ and it worked well. or different font faces to represent different sorts of identifier eg class names, tycons, value constructors, operators like `seq` as opposed to seq etc Lots of editors do this with monospaced fonts; I think it's orthogonal to the layout issue. For example on Windows Trebuchet MS is a very nice font, also Verdana, both of which are not monospaced. But yes I agree it's not a major issue and I just see the option of being able to use them as a nice side-effect. 3) Using only tabs ensures that vertical alignment goes to the same position on the screen regardless of the font and tabs could even have different widths just like in a wordprocessor Requiring tabs is a really bad idea. Just forget it. Seriously. I'm really puzled here. I've been using tabs to indent my C++ code for at least 10 years and don't see the problem. The only problem would be if someone mixed tabs with spaces. Since it has to be either tabs only or spaces only I'd choose tabs only to save keystrokes. I suppose though it is always going to be a matter of personal taste... 4) Any keypress has a localised effect on the parse tree of the buffer as a whole ( { " no longer kill everything which follows and there would be no {- ) I don't understand why this is an advantage. If you have an editor that highlights comments in green, then large sections of the program will flash green while you type a {- -} comment, which might be annoying, but it also means you'll never forget to close the comment, so the practical benefit of forbidding {- -}, as opposed to simply not typing it yourse
[Haskell-cafe] Layout rule (was Re: PrefixMap: code review request)
Brian Hulley wrote: Here is my proposed layout rule: 1) All layout keywords (where, of, let, do) must either be followed by a single element of the corresponding block type, and explicit block introduced by '{', or a layout block whose first line starts on the *next* line I wouldn't have much trouble adapting to that. and whose indentation is accomplished *only* by tabs You can't be serious. This would cause far more problems than the current rule. I would also make it that explicit braces are not allowed to switch off the layout rule (ie they can be used within a layout), I don't understand. What does "used within a layout" mean? multiline strings would not be permitted, They aren't now, except with \ escapes. A stray " will be caught on the same line unless the line happens to end with \ and the next line happens to begin with \, which is exceedingly unusual. and multiline comments would not be permitted (pragmas could easily be used just by using --#) But --# doesn't introduce a comment. And this would make UNPACK pragmas rather inconvenient to use. 1) When you see a ';' you could immediately tell which block it belongs to by looking backwards till the next '{' I guess that might be helpful, but it doesn't seem easier than looking left to the beginning of the current line and then up to the first less-indented line. 2) Variable width fonts can be used, They can be used now, if you adhere to a certain style, but not everyone likes that style. I wrote in C++ with a variable width font and tabs at one time, but eventually went back to fixed width. One reason was that I couldn't use comment layout conventions that tend (in my experience) to improve readability more than monospacing hurts it. Another reason was that glyph widths appropriate to natural languages didn't work all that well for source code. Spaces are much more important in source code than in natural language, for example. A proportional font designed for source code would be nice, but I haven't found one yet. Stroustrup used a mixture of proportional and monospaced glyphs in _The C++ Programming Language_ and it worked well. or different font faces to represent different sorts of identifier eg class names, tycons, value constructors, operators like `seq` as opposed to seq etc Lots of editors do this with monospaced fonts; I think it's orthogonal to the layout issue. 3) Using only tabs ensures that vertical alignment goes to the same position on the screen regardless of the font and tabs could even have different widths just like in a wordprocessor Requiring tabs is a really bad idea. Just forget it. Seriously. 4) Any keypress has a localised effect on the parse tree of the buffer as a whole ( { " no longer kill everything which follows and there would be no {- ) I don't understand why this is an advantage. If you have an editor that highlights comments in green, then large sections of the program will flash green while you type a {- -} comment, which might be annoying, but it also means you'll never forget to close the comment, so the practical benefit of forbidding {- -}, as opposed to simply not typing it yourself, seems nil. 5) It paves the way for a much more immersive editing environment, but I can't say more about this at the moment because I haven't finished writing it yet and it will be a commercial product :-))) I guess everything has been leading up to this, but my reaction is that it renders the whole debate irrelevant. The only reason layout exists in the first place is to make source code look good in ordinary text editors. If you have a high-level source code editor that manipulates the AST, then you don't need layout, or tabs, or any of that silly ASCII stuff. The only time you need to worry about layout is when interoperating with implementations that use the concrete syntax, and then there's nothing to stop you from exporting in any style you like. And when importing, there's no reason to place restrictions on Haskell's layout rule, because the visual layout you display in the editor need have no connection to the layout of the imported file. Using my self-imposed layout rule I'm currently editing all my Haskell code in a standard text editor using tabs set to 4 spaces and a variable width font and have no problems. Which is the best argument for keeping the current rule! If it were changed as you propose, then someday Hugh Briley would come along and complain that Haskell's layout syntax squandered screen space---but he *wouldn't* be able to program in his preferred style, because it would no longer be allowed. Religious freedom is a good thing. {- Ben -} ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe