med ∩ ml

Notes on Simple Made Easy

These are my notes on the talks “Simple Made Easy” by Rich Hickey.

Simplicity is a prerequisite for reliability - Dijkstra


  • One role.
  • One task.
  • One concept.
  • One dimension.
  • Lack of interleaving. (Does not mean there’s only one thing)


  • “Near”. To our understanding, skill/set or capabilities.
  • Easy is relative.

We can only make reliable those things we can understand.

We can only consider a few things at a time. If a piece is intertwined with another we already have to keep both in mind. It’s combinatorial.

Complexity undermines understanding.

Ignoring complexity slows you in the long haul.

The simple route is slower at the beginning because it requires thought.

Benefits of simplicity:

  • Ease of understanding.
  • Ease of change
  • Ease of debugging
  • Flexibility
    • Policy
    • Location

Complect = interleave, entwine, braid.

Compose = place together.

Modularity != simplicity. Partition and stratification (modularity) != simplicity.

Modularity = simplicity; when we limit what those modules are allowed to think about.

Programming, when stripped of all its circumstantial irrelevancies, boils down to no more and no less than very effective thinking so as to avoid unmastered complexity, to very vigorous separation of your many different concerns - Dijkstra

Simplicity is the ultimate sophistication - Da Vinci

Simple made easy

  • Chose simple constructs over complexity-generating constructs.
    • It’s the artifacts, not the authoring.
  • Create abstractions with simplicity as a basis.
  • Simplify the problem space before you start.
  • Simplicity often means making more things, not fewer.

The simplicity toolkit

Construct Get via
Values final, persistent collections…
Functions stateless methods
Namespace language support
Data Maps, arrays, sets, JSON…
Polymorphism a la carte Protocols, type classes
Set functions Libraries
Queues Libraries
Declarative manipulation SQL, Prolog
Rules Libraries, Prolog
Consistency Transactions, values…