Sketched out idea for extending protocols with additional protocol constraints

protocol-extension.js

const Eq = protocol(['a', 'b'], {
  eq: ['a', 'b'],
  neq: ['a', 'b']
})

const Ord = protocol(Eq('a', 'b'), ['a', 'b'], {
  gt: ['a', 'b'],
  lt: ['a', 'b']
})

Ord([String, String], {
  gt (a, b) { return a > b }
  lt (a, b) { return a < b }
}) // => ERROR: No implementation for extended protocol defined for [String, String]

// Multiple constraints, no genfuns, Applicative and Chain implementations directly in Monad
const Monad = protocol([Applicative, Chain], [], {
  // fantasy-land does not define any methods on Monad -- just the inheritance constraints
})

Applicative(Parser, {
  of() { ... }
})
Monad(Parser, {}) // => Error
Chain(Parser, {
  chain() { ... }
})
Monad(Parser, {})
Protocol.hasImpl(Monad, Parser) // true