<div dir="ltr"><div class="gmail_default" style="font-family:monospace,monospace">Have you considered laying it out somewhat differently?</div><div class="gmail_default" style="font-family:monospace,monospace"> ( if ... then</div><div class="gmail_default" style="font-family:monospace,monospace"> else if ... then</div><div class="gmail_default" style="font-family:monospace,monospace"> else if ... then</div><div class="gmail_default" style="font-family:monospace,monospace"> else</div><div class="gmail_default" style="font-family:monospace,monospace"> )</div><div class="gmail_default" style="font-family:monospace,monospace">It's *really* not a good idea to put semicolons at the end of lines</div><div class="gmail_default" style="font-family:monospace,monospace">as they are far too easy to confuse with commas.</div><div class="gmail_default" style="font-family:monospace,monospace"> </div></div> <div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, 22 Jul 2019 at 18:16, Julian Fondren <<a href="mailto:jfondren@minimaltype.com">jfondren@minimaltype.com</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hello, Please consider the following. I realize that daytype/1 would be better as just a bunch of disjunctions, but I'm using the example to show off different ways to format Mercury code: :- type days ---> sunday ; monday ; tuesday ; wednesday ; thursday ; friday ; saturday. :- func daytype(days) = string. daytype(D) = R :- ( D = wednesday -> R = "humpday" ; (D = sunday; D = saturday) -> R = "weekend" ; R = "workday" ). if/then/else seems to be the recommended style, but, I find it impossible to format in a pleasing way. Here are some attempts, and my problems with them: % this feels like the natural way. % but this is a level of indentation too many. % it looks OK here but not next to (A;B;C;D). daytype(D) = R :- ( if D = wednesday then R = "humpday" else if (D = sunday; D = saturday) then R = "weekend" else R = "workday" ). vs. % Mercury stdlib seems to have settled on this style. % the initial 'if' looks unbalanced vs. the rest of the code. daytype(D) = R :- ( if D = wednesday then R = "humpday" else if (D = sunday; D = saturday) then R = "weekend" else R = "workday" ). % trying to fix the previous version. % new problem: inconsistent indentation. daytype(D) = R :- ( if D = wednesday then R = "humpday" else if (D = sunday; D = saturday) then R = "weekend" else R = "workday" ). % trying to fix the inconsistency. % new old problem: this is a level of indentation too many. daytype(D) = R :- ( if D = wednesday then R = "humpday" else if (D = sunday; D = saturday) then R = "weekend" else R = "workday" ). Even if horizontal formatting is generally discouraged as a maintenance hassle, Mercury styling uses it a lot (and somewhat more conveniently than normal since it's aligned to tab stops), and it just looks really, really nice, for code that's not going to change a lot. daytype(D) = ( D = wednesday -> "humpday"; (D = sunday; D = saturday) -> "weekend"; "workday" ). With if/then: % This is somehow intolerable. With punctuation it looks like math % you'd write freehand on paper. Maybe that's why I like that % version. daytype(D) = ( if D = wednesday then "humpday" else if (D = sunday; D = saturday) then "weekend" else "workday" ). *Syntax* issues with languages, I'd normally disregard as trivial, but I don't think *formatting* is trivial. Formatting is so important that 1. languages like Python, Haskell, Nim, make it meaningful. 2. languages like Go (gofmt), Ada (gnatpp), Elm, make it automatic. You don't format your code; a code prettifier does. 3. JavaScript speakers like Douglas Crockford pretend that automatic semicolon insertion is a scaaaary, spooooky nondeterministic process that you can't trust with your code, in order to persuade devs to always use semicolons even though JS doesn't actually need them, because there are exactly *two* minor formatting problems that come up if you avoid semicolons as a rule. 4. ReasonML and Elixir are successful and popular 'languages' that are just skins over existing languages that are somewhat more annoying (Erlang string literals produce list(char) and to avoid that you write uglier <<"blah">> binary literals; OCaml has a toplevel/non-toplevel syntax distinction that people so routinely fail to understand that you'll see unnecessary ;; double semicolons all the time in newbie OCaml code). Maybe this is untrue, but my assumption for a while was that if/then/else was added to Mercury in the first place because people learning Mercury complained about formatting problems with the Prolog-style conditionals. This is odd as the new syntax retains any problem you'd have with the old syntax, but, even if people are aggravated by something, this doesn't mean they *recognize* what specifically they find aggravating. Maybe the formatting aggravation was always mis-explained as "words are easier to read than punctuation": 1. other languages use words rather than punctuation (true, but irrelevant) 2. other languages don't need to parenthesize their conditionals to mark where the conditionals end Maybe the water's long under the bridge, but an 'end' token instantly fixes the syntax in my view. daytype(D) = R :- if D = wednesday then R = "humpday" else if (D = sunday; D = saturday) then R = "weekend" else R = "workday" end. ... Well, having said all that, I've already realized that the unbalanced-if is what the stdlib is going with, so I'll try that and see if it eventually stops bothering me. I do think that the tutorial should reflect this style if that's what's recommended. Right now the tutorial has fib(N, X) :- ( if N =< 2 then X = 1 else fib(N - 1, A), fib(N - 2, B), X = A + B ). which is just... 1. an indention too many 2. the N =< 2 column isn't on a (4spc) tab stop. If fixed to lie on a tab stop (for writing/editing convenience), it's excessively indented and looks ugly. 3. that final 'else' looks bad and every other way to reformat it looks much, much worse. And then later, a four-space indentation, followed by a three-space indentation for if/then/else keywords, followed by a two-space indentation for the body of the conditional: main(!IO) :_ io.read_line_as_string(Result, !IO), ( if Result = ok(String), string.to_int(string.strip(String), N) then io.format("fib(%d) = %d\n", [i(N), i(fib(N))], !IO) main(!IO) else io.format("I didn't expect that...\n", [], !IO) ). I actually like Mercury's syntax, and how the language looks overall. I was even happy to discover that the omnipresent parentheses are really just mathematical parentheses for grouping, and that this is valid (if inadvisable): daytype(D) = R :- (D = sunday; D = saturday), R = "weekend"; (D = monday; D = tuesday; D = thursday; D = friday), R = "workday"; D = wednesday, R = "humpday". But I don't think anyone could read the tutorial, and try to recreate the examples as they're shown, and come to any other conclusion than that Mercury conditionals are very annoying to format. While reproducing the second example, in vim, I used visual block mode to delete a single space, rather than actually recreate that 3-space indent. _______________________________________________ users mailing list <a href="mailto:users@lists.mercurylang.org" target="_blank">users@lists.mercurylang.org</a> <a href="https://lists.mercurylang.org/listinfo/users" rel="noreferrer" target="_blank">https://lists.mercurylang.org/listinfo/users</a> </blockquote></div>