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## 2020-08-19

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```
(defn pascal [n]
(take n (iterate #(mapv (fn [[x y]] (+ x y)) (partition 2 1 (cons 0 (into % [0])))) [1])))
```

For a given row, if you prepend and append 0 and then break into (overlapping) pairs, then add each pair, you get the next rows.

😮 1

So you can have an infinite sequence of Pascal's triangle rows and you just take as many rows as you want.

You could safely use `(concat [0] % [0])`

instead of `(cons 0 (into % [0]))`

if you find that clearer -- `mapv`

is eager so you won't get a stack overflow from a lazy computation.

❤️ 1

also concat ~~is more forgiving about~~ **doesn't have subtle bug possibilities via** seq / vector conj location