Functional Programming

WebPPL looks like JavaScript, but in practice it should be treated as a functional fraction of JavaScript.

Contents

• Functional programming basics
  • WebPPL is a functional subset of JavaScript
  • What “functional programming” means here
  • A useful mental model
  • Key terms (short definitions)
  • Why this matters in probabilistic programming
  • Common pitfalls (and the FP-friendly alternative)
  • Executable micro-example: closures
  • Where to go next
• Cache (memoization)
  • What cache does
  • Why this matters for functional programming
  • When cache is safe: pure/deterministic computations
  • Example: caching an expensive deterministic computation
  • When cache is a modeling tool: one latent value per key
  • Good modeling example: a stable latent trait per individual
  • When cache is dangerous: you accidentally remove independence
  • Bad example: you wanted a fresh coin flip every time
  • A simple rule of thumb
  • See also
  • Executable example