First we define a function for computing the L₁ distance between two vectors:
let L1 [n] (xs: [n]f64) (ys: [n]f64) : f64 = map2 (-) xs ys |> map f64.abs |> f64.sum
We use the forward pipe operator in the definition above.
To compute the pairwise L₁ distances between all rows in a matrix, we
map over the rows twice, then compute the distances between two rows:
let pairwise_L1 [n][m] (xss: [n][m]f64) : [n][n]f64 = map (\a -> map (\b -> L1 a b) xss) xss
This pattern is very similar to matrix multiplication.