Question: should the expression (10 -23) throw syntax error?

[SomMeri]

Full code:

test-works {
  something: (10 -23); 
}

Error:

SyntaxError: expected ')' got '-' in c:\...\test.less on line 2, column 18:
1 test-works {
2   something: (10 -23);
3 }

It is probably related to this: #952

Tested on 1.4.0-b1 with windows node.js.

[jonschlinkert]

Interesting, it doesn't throw an error if you add a space on both side of the minus sign:

test-works {
  something: (10 - 23); 
}

but I confirmed that it does throw an error as you've written it

[lukeapage]

yes, it is interpreted as 10 and -23, two values in a space separated list, inside brackets.

At the moment the interpretation of brackets happens after parsing in less.js

[lukeapage]

.. therefore to fix it we would have to allow (12 (0 - 1)) to be valid or do something more complicated. I don't think it is a hardship to ask the user to clarify what they mean.

[matthew-dean]

But in parentheses, doesn't that force attempt of math?

[matthew-dean]

That is, is there a a valid value that has parentheses as the value (that isn't clearly a media block or a url or a registered LESS function) that wouldn't be math? If not, seems like we can assume math? Or is that a naive assumption?

[lukeapage]

yes it attempts maths on maths objects... e.g. the parser parses 1 + 3 and if in parenthesis then at evaluation time, that is converted into 4.. but at parse time this is parsed as two values.. the parser doesn't know about strict maths and whether two values should be added together.

So, the structure of the two trees is different... Parenthesis -> Value and Parenthesis -> Operation. Either the parser would have to be aware of context and treat it different, or at evaluation time Value would have to say "am I in parenthesis" and convert itself to an operation.

Making the parser aware of parenthesis and maths is probably the better solutuion, but a hell of a lot of effort for some less that is confusing and has never been parsed in the past.

[SomMeri]

Thank you for all explanations. I was writing blog post about less, run into this and got confused. I will put it into "quirks" chapter and leave it at that.

[SomMeri]

Hm, I tried to play around the idea somewhat more. Altrough I do not know how exactly less.js works, this task seems to be even more complicated.

Less lazy load variables and lazy evaluates expressions. So, if the solution would keep using lazy rules, the variable 1 -2 would have double meaning:

@list-or-expression: 1 -2;

#use {
  as-list: extract(@list-or-expression, 1); // compiles into "as-list: 1;"
  as-number: (@list-or-expression + 1);  // compiles into "as-number: 0;"
}

Ratio vs division works the same way, but they are closer to each other then list and expression:

@ratio-or-expression: 2/1;
#use {
  as-ratio: @ratio-or-expression; // compiles into "as-ratio: 2/1;"
  as-expression: (@ratio-or-expression + 1);  // compiles into "as-expression: 3;"
}

Bleh.

[lukeapage]

hrmm list-or-expression is pretty strange. That should probably err...?

[SomMeri]

Yes, this will currently err as-number: (@list-or-expression + 1); currently. It was meant as "what would it do if 1 -2 would be parsed also as an expression".

[lukeapage]

I think it is not worth fixing and we should keep it as a syntax error. It looks like it should be valid because in other languages space is not a separator converting it to a list.

Reading the mdn documentation on calc

https://developer.mozilla.org/en-US/docs/CSS/calc

In CSS calc(12px -1px) is invalid.. so given the complications, not supporting it in less either is IMO reasonable

[SomMeri]

I will close it then.