1° With left argument longer than one, the scalar is properly
extended to a higher rank one-element array, but then it's not
dropped correctly unless all axes are non-zero.
⊢X← 1 0↓2
2
⍴X
1 1
The X here should be an empty array (0 1⍴0) but is (1 1⍴2).
2° When left argument has one non-zero element and right is
a non-zero scalar, the returned result is a weird value that
looks like the correct one (0⍴0), but is distinct, and isn't
transferable.
8⎕CR Y← 1↓1
┌⊖┐
│0│
└─┘
⍬≡Y ⍝ should be true
0
(11⎕CR⍬)≡(11⎕CR Y)
1
Y ≡ 12⎕CR 11⎕CR Y
0
3° This might not be an error, but I find it surprising:
3 ≡ ''↓3 ⍝ this is correct
1
''↓⍳3 ⍝ this is an extension (length error by ISO)
2 3
''↓⍳3 3
LENGTH ERROR
''↓⍳3 3
^ ^
By my reading of ISO, when left argument is empty, the right
must be a scalar (or it will be a length error) which is
returned unchanged. In Dyalog it's extended such that any
value is returned unchanged, in GNU APL ⍬↓X ←→ 1↓X for
non-scalar X. Is this intended and correct? (Is that what
APL2 does?)
-k
