boxlang-functional-programminglisted

# BoxLang Functional Programming ## Overview BoxLang treats functions as first-class values. Functions can be stored in variables, passed as arguments, returned from other functions, and used in functional pipelines. BoxLang supports closures, lambdas, and arrow functions with a clean, expressive syntax. ## Closures vs Lambdas — Critical Distinction **This distinction matters for correctness:** | Syntax | Name | Scope Capture | Use When | |--------|------|---------------|----------| | `(args) => expr` | Closure | ✅ Yes — captures surrounding scope | Accesses outer variables or calls external functions/BIFs | | `(args) -> expr` | Lambda | ❌ No — only uses its own args | Purely deterministic; only works with passed arguments | | `function(...) {}` | UDF/Closure | ✅ Yes — when assigned to a variable/returned | Named or complex multi-line function bodies | ```boxlang var multiplier = 10 // ✅ Closure (=>) — captures 'multiplier' from outer scope var scale = ( n ) => n * multiplier scale( 5 ) // 50 // ✅ Lambda (->) — does NOT capture, only uses its own arguments var double = ( n ) -> n * 2 double( 5 ) // 10 // ❌ WRONG — lambda trying to access outer 'multiplier' will fail var scale = ( n ) -> n * multiplier // Error! multiplier not in lambda scope ``` **Rule of thumb:** If the function body references any variable from the surrounding scope or calls external functions/BIFs (like `now()`, `writeLog()`, etc.), use `=>` (closure). If it only processes its own arguments,