url Compile

[YYQH]

.IE6Background(@url: none) when (isstring(@url)){
    background-image: url('@{url}');
    _background-image: none;
    _filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src="@{url}",enabled=true,sizingMethod="crop");
}
.banner-des-bg4ie6{
    .IE6Background('../img/ui.png');
}

after Compile, I find the same url param ,but output two result

.banner .banner-img .banner-descript .banner-des-bg4ie6 {
  background-image: url('../lib/img/ui.png');
  _background-image: none;
  _filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src="../img/ui.png", enabled=true, sizingMethod="crop");
  margin: 0 -168px;
}

[seven-phases-max]

See --relative-urls.
So (assuming you're compiling with --relative-urls on) this is expected behaviour.
I.e. depending on you needs (providing you can't use url() for Microsoft.AlphaImageLoader), you either need to turn the option off or alternatively escape url identifier so Less won't process it, e.g.:

background-image: ~'url(@{url})';

Also please use backticks to format your code.

[YYQH]

In a function,the param usually is the same. so, I hope you could normalize parameter，also you could give up a function that can deal url when compile the file。thanks

[seven-phases-max]

so, I hope you could normalize parameter

The parameter is the same. The difference is in url('@{url}') and src="@{url}" statements: the first one is url but the second one is just a string hence the result (yet again see --relative-urls).

[YYQH]

thanks!
by the way，Less is very useful tools for writing CSS,but,one style part need one function, but when i need use one function do more things, I need write more function ,like the function overloading, for example:
.animation(@name, @duration: 500ms, @fn: ease, @delay:0, @count: 1, @direction: normal) when (iskeyword(@name)){
// ...
}
.animate(@name, @duration) when (@name = maskradi){
.animation(@name, @duration, ease-in-out);
// ...
}
.animate(@name, @duration, @width) when (@name = maskwipe){
.animation(@name, @duration, ease-in-out);
// ...
}
.animate(@name, @duration: 400ms, @top: 100px) when(@name = vertialjump){
.animation(@name, @duration);
// ...
}
so ,in future , Less could support more useful conditional statements in function, like 'if else'

[seven-phases-max]

Please use backticks to format your code. (I formatted you first post as an example but I won't be doing this for further posts).

As for you question, sorry, the issue tracker is not a forum. So for a generic Less "How-To" question please use SO. And for another issues/feature-requests search/create a dedicated ticket.

Either way, regarding the else functionality: first of all you can put conditional mixins into the main animation mixin. Beside there're plenty of features that cover all the multi-conditional use-cases just fine (logical expressions, pattern-matching, CSS guards, default() function etc. etc. etc. See corresponding examples in the docs)... Additionally see these SO Q&A queries: 1, 2 etc. for more practical guards usage examples.

[seven-phases-max]

Closing as expected behaviour.