| The library report defines
|
| -- Diagonal of a square matrix
| diag :: (Ix a) => Array (a,a) b -> Array a b
| diag x = ixmap (l,u) (\i->(i,i)) x
| where ((l,l'),(u,u')) | l == l' && u == u' = bounds x
And that is indeed a stupid definition. It's like saying
x = if x>2 then 1 else 10
(the guard is really just an 'if'.) So of course l, u etc are all
bottom.
The guard needs to be on diag itself
diag x | l==l' && u==u' = ixmap ...as before
where
((l,l'),(u,u')) = bounds x
thanks for pointing this out
| I am also curious why, for example,
|
| row :: (Ix a, Ix b) => a -> Array (a,b) c -> Array b c
| row i x = ixmap (l',u') (\j->(i,j)) x where ((l,l'),(u,u'))
| = bounds x
|
| isn't written as
|
| row :: (Ix a, Ix b) => a -> Array (a,b) c -> Array b c
| row i x = ixmap (l,u) (\j->(i,j)) x where ((_,l),(_,u)) = bounds x
| ~~~ ~~~ ~~~
you can write it either way
S
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