Dear all,
I am struggling with the translation of the following APL dyad to J:
∊ 0 {(⊢,(⍺+1)∇⊣)/⌽⍺,1↓⍵} y
which is the expression to yield a depth vector from a tree in record
format (drawn from Dr. Hsu's thesis). Demo:
t ← '∘'
ast ← t (t t) (t (t t) t) (t (t t t) (t t t) t)
∊ 0 {(⊢,(⍺+1)∇⊣)/⌽⍺,1↓⍵} ast
0 1 2 1 2 3 2 1 2 3 3 2 3 3 2
In particular, I don't understand the control flow and termination
condition for the recursion. Dr. Hsu says that this uses tree reduction
with no base case.
An attempt at a partial litteral translation as:
dv =. {{ (];(>:x) dv [)/\ |.x;}.y }}
results in an infinite loop. What am I missing? Is there some kind of
implicit termination condition in the ∇ primitive?
Thanks,
Raoul
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