The post is really talking about choosing the best kind of composition to solve problems in (purity was a by-product of being mathmatical). You guys are arguin

The post is really talking about choosing the best kind of composition to solve problems in (purity was a by-product of being mathmatical). You guys are arguing over the monadic io that he dismisses in the first couple couple paragraphs. All he really cares about is achieving program composition.