Fantasy Land // based on the specs described here https://github.com/fantasyland/fantasy-land

fantasyland.js

// Setoid

a.equals(a) === true // reflexivity
a.equals(b) === b.equals(a) // summetry
a.equals(b) && b.equals(c) == q.equals(c) // transitivity

// Ord
// must also implement the Setoid

a.lte(b) || b.lte(a) === true // totality
a.lte(b) && a.lte(a) == a.equals(b) // antisymmetry
a.lte(b) && b.lte(c) == a.lte(c) // transitivity

// Semigroupoid

a.compose(b).compose(c) === a.compose(b.compose(c)) // associativity

// Category
// must also implement the Semigroupoid

a.compose(C.id()) === a // right identity
C.id().compose(a) === a // left identity

// Semigroup

a.concat(b).concat(c) === a.concat(b.concat(c)) // associativity

// Monoid
// must also implement the Semigroup

m.concat(M.empty()) === m // right identity
M.empty().concat(m) === m // left identity

// Group
// must also implement the Monoid

g.concat(g.invert()) == G.empty() // right inverse
g.invert().concat(g) == G.empty() // left inverse

// Filterable

v.filter(x => p(x) && q(x)) == v.filter(p).filter(q) // distributivity
v.filter(x => true) = v // identity
v.filter(x => false) == w.filter(x => false) // annihilation

// Functor

u.map(a => a) == u // identity
u.map(x => f(g(x))) == u.map(g).map(f) // composition

// Contravariant

u.contramap(a => a) == u // identity
u.contramap(x => f(g(x))) == u.contramap(f).contramap(g) // composition