Building Composable Abstractions
- 1. Building Composable Abstractions: How to design software to stand the test of time. Eric Normand
- 2. How do we structure functional programs?
- 3. Why focus on abstractions? What is the process? Can we see an example? Conclusions
- 4. For the video and transcript of this presentation, click here: https://lispcast.com/oscon-building-composable-abstractions/
- 6. Aristotelian Physics (excerpt) Ideal speed Natural place Natural motion Unnatural motion
- 8. Newton’s Laws of Motion 1. Inertia 2. Acceleration 3. Action-reaction
- 10. –Eric Normand @ericnormand “Choice of abstraction matters. There is no way to refactor Aristotle into Newton.”
- 11. Process objectives • Consistently produces Newtonian abstractions • Anyone can do • Fosters collaboration
- 12. Inspired by Conal Elliott’s Denotational Design
- 14. Canvas
- 20. The Steps 1. Physical metaphor 2. Metaphor exploration 3. Model construction 4. Implementation
- 21. –Every experienced programmer, ever “Don’t just start writing code. Think about the problem first.”
- 22. 1. Physical metaphor 2. Metaphor exploration 3. Model construction 4. Implementation
- 23. Properties of a Good Metaphor Answers most questions Shared experience
- 25. –Eric Normand @ericnormand “Good metaphors contain answers to important questions. Different metaphors might have different answers to the same questions.”
- 27. –Eric Normand @ericnormand “I’ve never met a good abstraction I couldn’t turn into a good metaphor.”
- 28. • Our physical intuition is rich. • Contain answers to questions. • Keep you grounded while abstracting. • Discussable. Physical metaphor summary
- 29. 1. Physical metaphor 2. Metaphor exploration 3. Model construction 4. Implementation
- 30. –Every programming teacher ever “Focus first on the interface, not the implementation.”
- 31. • Cutouts have a color • Cutouts have a shape • Overlay order • Rotation and translation are independent • Rotation is additive • Translation is additive Notes about the interface
- 32. Cutouts have a shape • Cutout • Shape shapeOf(c)
- 33. Cutouts have a color • Cutout • Shape • Color colorOf(c )
- 34. Construct cutouts • Cutout • Shape • Color • Construct rect(color, w, h) circle(color, r)
- 35. Overlay order • Cutout • Shape • Color • Overlay overlay(a, b) ≠ overlay(b, a) What does overlay return? A cutout? Cutouts need a shape and color.
- 36. –Eric Normand @ericnormand “Avoid corner cases while you can. Each corner case is a branch. Branches multiply when you compose them.”
- 37. Overlay order (2) • Cutout • Color • Shape • Collage • Overlay overlay(collage, cutout) overlay(overlay(col, a), b) ≠ overlay(overlay(col, b), a)
- 38. Rotation and translation independence • Cutout • Color • Shape • Collage • Overlay • Translate • Rotate translate(rotate(a, r), x, y) = rotate(translate(a, x, y), r)
- 39. Rotation is additive • Cutout • Color • Shape • Collage • Overlay • Translate • Rotate rotate(rotate(a, r1), r2) = rotate(a, r1 + r2)
- 40. Translation is additive • Cutout • Color • Shape • Collage • Overlay • Translate • Rotate translate(translate(a, x1, y1), x2, y2) = translate(a, x1 + x2, y1 + y2) too many concepts
- 41. –Eric Normand @ericnormand “Composition is usually the hardest kind of operation to implement. We should develop those first because they will constrain our design choices.”
- 42. Overlay order (3) • Cutout • Overlay overlay(a, b) overlay(a, b) ≠ overlay(b, a)
- 43. Rotation and translation independence • Cutout • Overlay • Translate • Rotate translate(rotate(a, r), x, y) = rotate(translate(a, x, y), r)
- 44. Rotation is additive • Cutout • Overlay • Translate • Rotate rotate(rotate(a, r1), r2) = rotate(a, r1 + r2)
- 45. Translation is additive • Cutout • Overlay • Translate • Rotate translate(translate(a, x1, y1), x2, y2) = translate(a, x1 + x2, y1 + y2)
- 46. Construct colors color(r, g, b) • Cutout • Overlay • Translate • Rotate • Color
- 47. Construct cutouts rect(color, w, h) circle(color, r) • Cutout • Overlay • Translate • Rotate • Color
- 48. We forgot to draw • Cutout • Overlay • Translate • Rotate • Color • Draw draw(cutout)
- 49. Step 2 Summary • Sketch out operations and relationships between operations. • Focus on composition first. • No corner cases.
- 50. 1. Physical metaphor 2. Metaphor exploration 3. Model construction 4. Implementation
- 51. We need representations • Cutout • Overlay • Translate • Rotate • Color • Draw Number String Object Array Function …
- 52. –Eric Normand @ericnormand “Choose constructs that have the properties you’re looking for.”
- 54. Functions outpu t inputs (things that change) variables in environment (things that don’t change)
- 55. Colorconstructor function things that don’t change nothing that changes
- 56. –Eric Normand @ericnormand “If you really want to see how an abstraction composes, represent it as a function.”
- 57. Rectangles translation and rotation can change color and shape do not change call color function cutout is a function
- 58. Circles
- 59. Translation cutout is a function call cutout with new translation
- 60. Rotation cutout is a function call cutout with new rotation
- 61. Overlay
- 62. draw!
- 65. Overlay
- 66. –Eric Normand @ericnormand “Revisit your physical metaphor. It contains the answers.”
- 69. Step 3 Summary • Choose existing constructs that have properties. • Revisit the metaphor if there are problems.
- 70. 1. Physical metaphor 2. Metaphor exploration 3. Meaning construction 4. Implementation
- 71. –Well-meaning OOP programmers everywhere “Just use a class.”
- 72. Conclusions
- 73. Process objectives • Consistently produces Newtonian abstractions • Anyone can do • Fosters collaboration
- 74. Corollaries • Know your domain (metaphor) • Know your language (meaning)
- 75. Is your system Aristotelian or Newtonian?
- 76. Eric Normand Follow Eric on: Eric Normand @EricNormand eric@lispcast.comlispcast.com