The problem is that the function has multiple statements ⍺←2 and ⍵*÷⍺ but what you’ve put into the notebook document is just a single statement ⍺←2 ⍵*÷⍺ =. You can separate statements with ⋄ as in root ← {⍺←2 ⋄ ⍵*÷⍺} or use `]dinput to indicate that this notebook block defines a multiline function:
]dinput
root ← {
⍺←2
⍵*÷⍺
}
Similarly, for the function with a guard, write root ← {⍺=0:0 ⋄ ⍵*÷⍺} or
]dinput
root ← {
⍺=0:0
⍵*÷⍺
}
We’ll look into making this automated in the future, so you can omit ]dinput.