@ConradIrwin

One line of ruby!

def repl
  loop{ puts eval $stdin.readline }
end

12,000 lines of ruby!

require 'pry'
binding.pry

REPL-driven development

• Don't write code first.
• Don't write tests first.
• Use the REPL first.

P(bug)

• When you write code: ~0.8
• Github production: ~0.000000008*

* Github exception-% this week is 0.0008%, assume 1000 method-calls per request.

100,000,000 times better?

• Run the code → 1000 times better?
• Read the code → 100 times better?
• Understand the code → 1000 times?

100,000,000 times better?

• Run the code → takes seconds?
• Read the code → takes minutes?
• Understand the code → takes days?

Pry

• Easy to run the code!
• Easy to read the code!
• Helps to understand the code...*

* Though I usually git clone if I need this.

DEMO

Recap

• ls shows methods.
• $ (show-source) shows code.
• ? (show-doc) shows documentation.

Downsides of REPL

• Doesn't keep a record.
• You have to re-test lots.
• Hard to test large apps.

Solution: Tests

Tests help

• When code-base is large.
• With API design.
• Document assumptions.

Downsides of Tests?

• Slow to write.
• Slow to run.
• Go out of date.

Pry can help!

• gem install pry-plus
• require 'pry-rescue/minitest'
• require 'pry-rescue/rspec'

DEMO

Recap

• try-again
• break
• step / next
• play
• edit

Even with testing

• Bugs slip through.
• Become harder to catch.
• Require longer to debug.

• Catches exceptions in production.
• Captures data to help you debug.
• Notifies you intelligently.

Fixing bugs

• Reproduce locally.
• Find problem.
• Fix it.

DEMO

Recap

• binding.pry
• cd
• up / down
• whereami
• help

Use a REPL

• Saves time
• Improves quality
• More fun!

Use Pry!

• Featureful
• Robust
• Friendly

@ConradIrwin