While And Until

While

• The while statement repeats a block of code while a condition is true.

Example

while boolean (
   command
   command
)

Syntax

while condition (
    commands
)

• condition: The condition that determines whether to continue executing the block of commands.

• commands: The commands to be executed within the loop.

Example

while distance_to_object < 10 (
    robot "moveForward" 10
    robot "turnLeft" 10

    robot "get_data"
    distance_to_object = robot."sensor1"
)

In this example, the robot will keep moving forward and turning left as long as there is an obstacle ahead.

Until

• The until statement repeats a block of code until a condition is true.

Example

until boolean (
   command
   command
)

Syntax

until condition (
  commands
)

• condition: The condition that determines whether to stop executing the block of commands.

• commands: The commands to be executed within the loop.

Example

until isGoalReached (
  // do things to get to goal
)

In this example, the robot will keep moving forward until the goal is reached.

Use Cases

1. User Input Validation with while

// Ask for user input until a valid value is entered
userInput = null
while userInput != null (
  userInput = "hello".ask()
  // keep asking until the user answers
)

This example demonstrates how the while statement can be used to repeatedly prompt the user for input until a valid value is entered.

1. Waiting for External Event with until

// Wait until a sensor detects an object
objectDetected = false
until objectDetected (
  robot "get_data"
  objectDetected = robot.detected
)

Here, the until statement is used to wait until a sensor detects an object before proceeding with the next set of commands.

Incrementing Loop Counters

When using counters in loops, note that the ++ operator cannot be used as a standalone statement. Instead, use assignment operators like += or full assignment:

i = 0
while i < 5 (
  log i
  i += 1      // Valid: increment with assignment operator
)

// Alternative
i = 0
while i < 5 (
  log i
  i = i + 1   // Also valid: explicit assignment
)

// NOT valid:
// i++         // SyntaxError: Cannot use '+' here