Logic and expressions¶

Numeric expressions and conditions are separate types. ty rejects using score > 0 as a movement distance or score + 1 as an if_then condition.

from itchy import control
from itchy.control import if_
from itchy import move


control.repeat_until(score >= 3, score.add(1))

decision = (
    if_(score.equals(3))
    .then_([move.x(score * 4), score.add(1)])
    .else_([score.reset()])
)

Branch bodies accept ordinary lists, nested lists, or individual commands. if_(...).then_(...) is a complete command without an else branch; if_(...) alone is an incomplete builder and ty rejects it in a script. The older if_then and if_else functions remain available.

Numeric reporters¶

Num is a numeric expression. +, -, *, and / build arithmetic reporters, including reflected operations such as 10 - score. go_to, move_x, set, and add accept numeric literals or expressions. repeat accepts a numeric literal or reporter count.

Comparisons <, >, <=, and >= generate conditions. Use .equals(value) for Scratch equality. Python == is object equality and does not generate a Scratch comparison.

Boolean composition¶

from itchy import control, sensing
from itchy.control import if_
if_(sensing.key_down(Key.SPACE) & (health > 0)).then_(award_points(1))

Use &, |, and ~ for AND, OR, and NOT. Parenthesize comparisons when composing them. Python and, or, not, if, and while evaluate at build time; conditions raise an error if coerced to a Python boolean. Avoid Python chained comparisons such as 0 < score < 10; write (score > 0) & (score < 10).

operators.random_number(low, high) generates a random numeric reporter evaluated at runtime. control.wait(seconds) yields for wall-clock time. These are not deterministic under the current headless tick adapter.

sensing.key_down(Key.RIGHT) generates a key-state reporter. sensing.touching(sprite) generates renderer-based collision sensing. A sprite name string, _edge_, or _mouse_ is also accepted; ordinary sprite names are checked during compilation.

Control sequences¶

Builder	Scratch behavior
`if_(condition).then_(steps).else_(other_steps)`	Select a branch using the fluent API
`if_(condition).then_(steps)`	Run a single conditional branch
`control.if_then(condition, *steps)`	Run the body when true
`control.if_else(condition, then=steps, otherwise=steps)`	Select a branch
`control.repeat(count, *steps)`	Repeat a literal or reporter number of times
`control.repeat_until(condition, *steps)`	Repeat while the condition is false
`control.forever(*steps)`	Keep repeating until stopped

Order initialization with messages¶

Green-flag scripts run concurrently. Reset shared state before announcing that a round is ready:

from itchy import events
from itchy import move

ready = Message("ready")

events.on_start(move.to(0, 0), score.reset(), events.broadcast(ready))
events.on_message(ready, prepare_coin, watch_for_player)

Declare ready in Game.messages. events.broadcast(ready, wait=True) waits for receiver scripts to complete; do not wait for a receiver that contains a forever loop.