  I present a formal connection between algebraic effects and game semantics,
two important lines of work in programming languages semantics with
applications in compositional software verification.
  Specifically, the algebraic signature enumerating the possible side-effects
of a computation can be read as a game, and strategies for this game constitute
the free algebra for the signature in a category of complete partial orders
(cpos). Hence, strategies provide a convenient model of computations with
uninterpreted side-effects. In particular, the operational flavor of game
semantics carries over to the algebraic context, in the form of the coincidence
between the initial algebras and the terminal coalgebras of cpo endofunctors.
  Conversely, the algebraic point of view sheds new light on the strategy
constructions underlying game semantics. Strategy models can be reformulated as
ideal completions of partial strategy trees (free dcpos on the term algebra).
Extending the framework to multi-sorted signatures would make this construction
available for a large class of games.
