Support more "isdatatype" functions

[Justineo]

We've got already quite a few such functions like iscolor, isstring, etc.

I think it's good to add more such kind of functions such as islength, isangle, istime, isposition, isresolution or even something like iscolorstop. This should make writing guardian expressions easier if we want to "overload" mixins.

[lukeapage]

We have

isunit(15px, px) // true

[Justineo]

isdatatype is quite different here. For example, islength equals a bunch of isunit checks and will greatly simplify the type check.

And some isdatatype functions can process more complex arguments such as:

isposition(top left) // true
iscolorstop(red 80%) //true

[lukeapage]

I can see how this would be useful writing library code

[Justineo]

As Less 1.7.0 started to support using ruleset as mixin parameters, I think isruleset should be a necessary type check function now.

[lukeapage]

Fair point.

[seven-phases-max]

Could we have one generic function, e.g. is(value, type-identifier), instead of writing a dedicated one every time?

[seven-phases-max]

Speaking of "composite" CSS types (as opposed to native Less types like ruleset) and functions like isposition or iscolorstop. I don't think it's a good idea to have this in the core, simply because the number of such "composite" types is literally infinite. How about isbackground(radial-gradient(5em circle at top left, yellow, blue), url(a.png) bottom left no-repeat, hsl(12, 34%, 56%) url("metal.jpg") top center / 100% auto no-repeat); // true? :)

I guess the plugins and/or #538 is the solution in this case.

[matthew-dean]

Could we have one generic function, e.g. is(value, type-identifier), instead of writing a dedicated one every time?

+1 Seems easier to maintain and document.

[stale]

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