030: Debugging in Elm

• Rubber ducking
• Lay out your assumptions explicitly
• Veritasium video The Most Common Cognitive Bias

Elm Debugging techniques

• Debug.todo
• Frame then fill in
• Annotation let bindings
• Using nonsense names as a step
• Elm review rule to check for nonsense name

Hardcoded values vs debug.todo

• Todos don't allow you to get feedback by running your code
• TDD
• Fake it till you make it
• Simplest thing that could possibly work
• Joël Quenneville's article Classical Reasoning and Debugging
• Debugging is like pruning a tree

Breaks

• Take a walk. Step away from the keyboard when you're grinding on a problem
• sscce.org (Short, Self Contained, Correct (Compilable), Example)
• Create a smaller reproduction of the problem
• Reduce the variables, you reduce the noise and get more useful feedback
• Reasoning by analogy from Joël's post
• Elm debug log browser extension
• node --inspect
• elm-test-rs

Debug.log in unit tests

• Test.only for running just one test or describe
• Put Debug.logs in each path of an if or case expression
• Use the browser elm debugger to inspect the model
• Scaling Elm Application episode
• Narrow down your search space with Elm types
• Parse, Don't Validate episode
• Tiny steps help you prune the tree
• Exploratory Testing
• Wrap early, unwrap late