There is more than one physics lib for Haxe and they are separate to the language, the canvas referenced may well be the canvas in the HTML5 compile target or are you mentioning the display list. You don't even have to use that if you target c++, neko or haxe because of another lib; waxe.

Haxe is a language and you can browse the libs available for its compile targets at http://lib.haxe.org/.

If you want to find out more about a framework that uses Haxe and is oriented towards mobile gaming (but not only towards that) checkout HaxeNME.

If you want a nice mature game engine lib built for Haxe try awe6 in the search at http://lib.haxe.org.

Haxe isn't lacking in the game engine department, thing is you can use Haxe with externals for node.js, a lib like noxe that extends haxe to node or simply use whatever javascript lib you feel like and output js. Or use the pure data lib to interact with mobile. Haxe isn't restricted to gaming. It's just one of the things the language allows for.

What you are asking is akin to asking what English is lacking to become a poem. HaXe is a language, not an engine.

First, haXe describes itself as a programming language.

Second, I don't see a mention of a physics engine builtin to haXe anywhere on the features page,

http://haxe.org/doc/features

where are you seeing that?

You're correct. I saw this earlier, but apparently it's not included in Haxe core:

http://haxe.org/com/libs/physaxe

Arguably the best 2d physics engine, http://deltaluca.me.uk/ is made with HaXe.

Better than Box2D..? (C++, various ports)

Yeah, played with both.