From Arrays to Lists
JavaScript calls them arrays. Ruby calls them arrays. But in Elo, we decided to call them Lists. Why? Because “array” implies fixed-size, indexed access. Elo’s collections are more like functional lists: you map over them, filter them, reduce them.
Similarly, what JavaScript calls objects became Tuples in Elo. Not because they’re immutable (they’re not), but because the term better reflects their use as structured records with named fields.
The rename rippled through everything: documentation, error messages, type names, stdlib functions.
Grammar Restrictions
Day four also locked down the grammar. Capital letters now have meaning:
- Uppercase names: Reserved for Types and Selectors (
String,Date<iso8601>) - Lowercase names: For everything else (variables, functions)
This isn’t just style—it’s enforced by the parser. Writing let Date = 5 in Date is now a syntax error. The restriction makes code self-documenting: you can tell at a glance whether something is a type or a value.
The Underscore Convention
Every Elo program now implicitly receives its input as _. This simple convention enables powerful patterns:
let user = { name: null } in user.name | 'Anonymous'
The input is always there, waiting to be accessed. No need to declare parameters for the common case.
Lambda Sugar
Writing fn(x ~> x * 2) is fine, but for single-parameter lambdas, (x ~> x * 2) is cleaner. Day four added this syntactic sugar—a small change that makes functional code more pleasant to write and read.
Good vocabulary reduces cognitive load. Good grammar prevents mistakes. Both make the language more approachable.