Relating Idioms, Arrows and Monads from Monoidal Adjunctions

Idioms are Oblivious, Arrows are Meticulous, Monads are Promiscuous

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...

Generalising monads to arrows

Strong Functors and Monoidal Monads

In [4] we proved that a commutative monad on a symmetric monoidal closed category carries the structure of a symmetric monoidal monad ([4], Theorem 3.2). We here prove the converse, so that, taken together, we have: there is a 1-1 correspondence between commutative monads and symmetric monoidal monads (Theorem 2.3 below). The main computational work needed consists in constructing an equivalenc...

Monads and Adjunctions for Global Exceptions

In this paper, we look at two categorical accounts of computational effects (strong monad as a model of the monadic metalanguage, adjunction as a model of call-bypush-value with stacks), and we adapt them to incorporate global exceptions. In each case, we extend the calculus with a construct, due to Benton and Kennedy, that fuses exception handling with sequencing. This immediately gives us an ...

Arrows, like Monads, are Monoids

Monads are by now well-established as programming construct in functional languages. Recently, the notion of “Arrow” was introduced by Hughes as an extension, not with one, but with two type parameters. At first, these Arrows may look somewhat arbitrary. Here we show that they are categorically fairly civilised, by showing that they correspond to monoids in suitable subcategories of bifunctors ...