cat/monoid

Monoid type {minimal implementation - mempty and mappend}.
Default implementation for the mconcat function (defined in terms of mempty and mappend).

Types

Monoid

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A monoid is a set with a binary operation or a a single object category with a set of morphisms that follow the rules of composition.

class Monoid m where
  mempty  :: m
  mappend :: m -> m -> m

Laws:

mappend mempty x = x
mappend x mempty = x
mappend x (mappend y z) = mappend (mappend x y) z
mconcat = foldr mappend mempty

Examples

let int_sum_monoid = Monoid(mempty: 0, mappend: fn(x: Int, y: Int) { x + y })
int_sum_monoid
|> mconcat([2, 3, int_sum_monoid.mempty, 4])
|> int_sum_monoid.mappend(10)
// -> 19
let bool_and_monoid = Monoid(mempty: True, mappend: bool.and)
True
|> bool_and_monoid.mappend(False)
|> bool_and_monoid.mappend(bool_and_monoid.mempty)
// -> False

pub type Monoid(m) {
  Monoid(mempty: m, mappend: fn(m, m) -> m)
}

Constructors

Monoid(mempty: m, mappend: fn(m, m) -> m)

Values

mconcat

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pub fn mconcat(mono: Monoid(m), monoid_list: List(m)) -> m

Fold a list of monoids using mappend.

Examples

int_prod_monoid
|> mconcat([2, 3, int_prod_monoid.mempty, 4, int_prod_monoid.mempty])
|> int_prod_monoid.mappend(10)
// -> 240