关于ask turtles中let变量作用域及并行执行逻辑的技术问询

Great question—let’s break this down clearly since NetLogo’s turtle execution model can be easy to misinterpret!

Absolutely, any variable you define with let inside an ask turtles block is unique to each individual turtle. Think of it like each turtle gets its own temporary scratchpad: when the block runs, every turtle creates its own instance of the let variable, uses it for its own execution of the block, and then discards it once it’s done.

For example, if you run this code:

ask turtles [
  let my-distance distance patch 0 0
  show (word "I'm " my-distance " units from the origin!")
]

Each turtle will calculate its own distance to the center patch, store that value in its own my-distance variable, and print a unique message. None of the turtles can access or modify another’s my-distance variable—they’re completely isolated.

NetLogo’s ask turtles uses what’s called logical parallelism, not true simultaneous execution. Here’s the key breakdown:

• The entire code block is run per turtle, but NetLogo cycles through each turtle one at a time to execute the full block. It just does this so quickly that it feels like all turtles are acting at once.
• Turtles do not execute individual lines of the block in parallel. Instead, each turtle runs the entire sequence of instructions in the block before the next turtle starts.
• A critical detail: NetLogo buffers all state changes (like moving, changing color, or updating variables) during the ask block. None of these changes are visible to other turtles until the entire ask block finishes executing. This prevents race conditions where one turtle’s mid-block action affects another’s execution.

For example, if you write:

ask turtles [
  fd 5
  set color blue
]

Turtle 0 will first move forward 5 steps, then turn blue. Then Turtle 1 does the same, then Turtle 2, and so on. You won’t have a mix of some turtles moving while others change color—each completes the full block before the next starts. And until all turtles finish, you won’t see any of their movements or color updates on the screen.

内容的提问来源于stack exchange，提问作者pablo