Growing a DSL for financial calculations
summary
Rabobank mortgage calculations move from opaque Java BigDecimal code into a small internal Scala DSL with full compile‑time checks, custom Amount and Percentage types, a Quantity type class to make multiplication safe, and a Period/Per design that enforces amount per month vs amount per year. The team replaces confusing literals (that stray 1200) with typed constructs, reuses existing Java tests to validate correctness, and business analysts begin reading and even committing DSL rules; code is open sourced.
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chapters (13)
- 0:00Intro
- 0:54Rabobank
- 3:49Java code
- 8:50Scala code
- 11:07Multiplication
- 11:33Type classes
- 14:08Implicit multiplication
- 14:35Monthly and yearly amounts
- 16:45Infix notation
- 18:53Summary
- 19:14The code
- 24:44New project
- 26:04Questions
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