ifelse-value is a primitive that allows us to quickly and concisely check a number of conditions and pick a value accordingly. This primitive helps us not write many consecutive if or ifelse statements.

For example, if we wanted to check which of the four quadrants of the world a given turtle is in, our first option is to write a code as follows:

to-report where-am-i
  if xcor > 0 and ycor > 0 [
        report "upper-right"
  ]
  if xcor < 0 and ycor > 0 [
        report "upper-left"
  ]
  if xcor < 0 and ycor < 0 [
        report "lower-left"
  ]
  if xcor > 0 and ycor < 0 [
        report "lower-right"
  ]
end

However, this many if statements make it hard to read the code. Instead, we can use the ifelse-value primitive as follows to make a much more concise code:

to-report where-am-i
  report (ifelse-value
        xcor > 0 and ycor > 0 ["upper-right"]
        xcor < 0 and ycor > 0 ["upper-left"]
        xcor < 0 and ycor < 0 ["lower-left"]
        ["lower-right"] ; if none of the conditions are true
  )
end

Things to keep in mind when using ifelse-value:

• You should wrap the whole ifelse-value within parentheses ().
• You can provide a last set of commands within brackets but without any preceding condition(s). This last set of commands will be treated like an else statement, specifying what will happen if none of the conditions are true. You can also omit this final condition.

In the model example below, we have six dice shapes. Every time we click the roll-all button, each turtle picks a random number between 1 to 6. Then, we use the ifelse-value primitive to pick the correct turtle shape to represent the corresponding die value.