You are confusing algorithms (Operational Semantics) with definitions (Denotational Semantics). One of the key difference between mathematics and computing is that mathematics is far less concerned with constructing results, and far more concerned with reasoning about the properties of objects. Mathematics sits at a level of abstraction unsuited to physical hardware.

In Haskell, this is evident in the complex and difficult to reason about graph-reduction engine that lays hidden in the runtime. Denotional semantics => Haskell Math yay. Operational Semantics => Haskell's downfall in real-world programmers.