The post is a pretty childish rant. One of the great facets of mathematical writing (and not learning, unfortunately) is that you can explicitly define your own

The post is a pretty childish rant. One of the great facets of mathematical writing (and not learning, unfortunately) is that you can explicitly define your own notation, and then use said notation whenever you want. The author even notes this in his final paragraph, but doesn't seem to see it as an advantage of mathematical writing. Prior to modern notation, mathematics was written out in english in full. What we have now is significantly better than what existed before modern mathematical shorthand. Also, the expectation is an operator and not a 'function' (in the sense that it does not take values in one of the canonical scalar fields e.g. R, C). The notation makes perfect sense in this setting. For example, the expression E[x^2] should be interpreted as E acting on the function x -> x^2 and not on a number x.