Recent investigations of lax algebras—in generalization of Barr’s relational algebras—make an essential use of lax extensions of monad functors on Set to the category Rel(V) of sets and V-relations (where V is a unital quantale). For a given monad there may be many such lax extensions, and different constructions appear in the literature. The aim of this article is to shed a unifying light on t...

Monads are a technique widely used in functional programming languages to address many different problems. This paper presents extensions, a functional-logic programming technique that constitutes an alternative to monads in several situations. Extensions permit the definition of easily reusable functions in the same way as monads, but are based on simpler concepts taken from logic programming,...

monoid can be defined. Monoidal categories are ubiquitous: cartesian categories (in particular, the category of sets), free word-category over any category, endofunctors category over any category, category of R-modules over a commutative ring R, etc. The abstract monoids definable in the monoidal category incarnate in the usual monoids, triples (or monads), R-algebras, etc. 2 Given a monoidal ...

An algebraic characterization of monads which are abstract partial map classi$ers is provided, without the assumption that the categories of total maps possess products. By an abstract partial map classi$er we mean a monad whose Kleisli category is a full subcategory of a partial map category wherein the induced comonad classi$es partial maps in the usual sense. A construction of the correspond...

Monads serve the abstract encapsulation of side effects in semantics and functional programming. Various monad-based specification languages have been introduced in order to express requirements on generic side-effecting programs. A basic role is played here by global evaluation logic, concerned with formulae which may be thought of as being universally quantified over the state space; this for...

We develop an algebraic underpinning of backtracking monad transformers in the general setting of monoidal categories. As our main technical device, we introduce Eilenberg–Moore monoids, which combine monoids with algebras for strong monads. We show that Eilenberg–Moore monoids coincide with algebras for the list monad transformer (‘done right’) known from Haskell libraries. From this, we obtai...

We revisit the connection between three notions of computation: Moggi’s monads, Hughes’s arrows and McBride and Paterson’s idioms (also called applicative functors). We show that idioms are equivalent to arrows that satisfy the type isomorphism A;B ' 1 ; (A→ B) and that monads are equivalent to arrows that satisfy the type isomorphism A; B ' A → (1 ; B). Further, idioms embed into arrows and ar...

We consider three monads on Top, the category of topological spaces, which formalize aspects probability and possibility in categorical terms. The first one is Hoare hyperspace monad H, assigns to every space its closed subsets equipped with lower Vietoris topology. second V continuous valuations, also known as extended probabilistic powerdomain. construct both a unified way terms double dualiz...