While it's not as full as OCR, there's an app called DeTeXify that will do almost exactly what you describe.

Android app link here: https://play.google.com/store/apps/details?id=coolcherrytree...

The stuff we do under-the-hood would make this relatively simple to implement. We already have a custom, intermediate, math expression language which we use to hold scanned data. One would only need to write a converter from this language to latex instead of the visual typesetting that we display on-screen

I'm betting that interpreting your math handwriting would be quite a bit harder than interpreting printed text. That said, I'd love to have that feature, too.