Variables & Expressions

Alpha (v0.1). Breaking changes expected.

Variables

Variables are immutable by default. Once bound, they can’t be reassigned — but you can shadow them:

name = "Keel"
name = "Keel v2"    # shadows the previous binding — original value is gone

Agent state fields are the exception — they’re mutable via self.:

agent Counter {
  state { count: int = 0 }

  task increment() {
    self.count = self.count + 1   # mutable state
  }
}

Type annotations

Type annotations are optional — the compiler infers types. But you can add them:

x = 42              # inferred as int
y: int = 42         # explicit annotation
z: float = 3.14     # explicit

Arithmetic

x = 2 + 3 * 4       # 14 (standard precedence)
y = 10 / 3           # 3 (integer division)
z = 10.0 / 3.0       # 3.333... (float division)
r = 17 % 5           # 2 (modulo)

Comparison

5 > 3                # true
"abc" == "abc"       # true
x != none            # true if x is not none

Boolean logic

true and false       # false
true or false        # true
not true             # false

if x > 0 and x < 100 {
  notify user "in range"
}

Null coalescing

The ?? operator provides a default when the left side is none:

name = user_input ?? "anonymous"
port = env.PORT.to_int() ?? 3000
result = classify text as Mood ?? neutral

Pipeline operator

Chain operations with |>:

email |> triage |> respond |> log

# Equivalent to:
log(respond(triage(email)))

# With extra arguments:
email |> triage |> respond(tone: "friendly") |> log("email_responses")

Field access

email.subject                  # field access
email?.subject                 # null-safe — returns none if email is none
email!.subject                 # null assertion — throws if email is none

env.API_KEY                    # environment variable
self.count                     # agent state field

Struct and list literals

# Struct (map)
person = {name: "Alice", age: 30, active: true}

# List
items = [1, 2, 3, 4, 5]

# Nested
records = [
  {name: "Alice", score: 95},
  {name: "Bob", score: 87}
]