He's contrasting it to languages that are closely based on a mathematical ideal, such as Haskell (pure functional programming, category theory, etc.) or Prolog

He's contrasting it to languages that are closely based on a mathematical ideal, such as Haskell (pure functional programming, category theory, etc.) or Prolog (Horn clauses and logic), minimalistic Scheme/Lisps (lambda calculus) or, to a lesser extent, SQL (relational theory, albeit a far from perfect implementation).