Lambda Expressions

Lambdas are anonymous functions used as arguments to higher-order standard library functions such as Map, Where, Reduce, Find, All, Any, SortBy, and Each.

Syntax

x => x * 2                          # Single parameter
(x, y) => x + y                     # Multiple parameters
(acc, item) => acc + item.price      # Used with Reduce

Parentheses around the parameter list are optional for single-parameter lambdas. They are required for multiple parameters.

Single-Expression Body

The body of a lambda is a single expression - not a block of statements. The value of the expression is implicitly returned.

# Valid - single expression
var doubled = Map(Data.numbers, x => x * 2)

# NOT valid - blocks are not supported in lambdas
# var doubled = Map(Data.numbers, x => { var result = x * 2; return result })

Closures

Lambdas capture variables from the enclosing scope:

var threshold = 100
var big = Where(Data.items, x => x > threshold)    # Captures 'threshold'

Common Patterns

# Transform
var doubled = Map(Data.numbers, x => x * 2)
var upper = Map(Data.names, n => ToUpper(n))

# Filter
var adults = Where(Data.users, u => u.age >= 18)
var evens = Where(Data.numbers, x => x % 2 == 0)

# Aggregate
var total = Reduce(Data.items, (sum, item) => sum + item.price, 0)

# Search
var first = Find(Data.items, x => x.status == "pending")

# Check
var anyExpired = Any(Data.items, x => x.expired)
var allValid = All(Data.items, x => x.price > 0)

# Sort by computed key
var byPrice = SortBy(Data.items, x => x.price)

Lambda vs Query Functions

For simple single-field comparisons, prefer the query functions (WhereByField, FindByField, etc.) - they are more concise. For complex conditions involving multiple fields or computed values, use lambdas.

# Simple field comparison - prefer query
var active = WhereByField(Data.users, "active", "==", true)

# Complex condition - prefer lambda
var eligible = Where(Data.users, u => u.age >= 18 and u.active and u.balance > 0)