Additionally lambda calculus, general recursive functions, combinatorial logic, Turing machines, and a number of other systems are equivalently powerful[0] and

Additionally lambda calculus, general recursive functions, combinatorial logic, Turing machines, and a number of other systems are equivalently powerful[0] and so any computable function can be expressed in any of the systems. So it's fine to refer either to purely functional algorithms or purely state-machine algorithms since they are equivalent statements. [0] https://en.m.wikipedia.org/wiki/Church%E2%80%93Turing_thesis https://en.m.wikipedia.org/wiki/Church%E2%80%93Turing_thesis