In Dyalog this is part of a consistent extension whereby you're allowed to use a "short left argument" to Take and Drop (and Squad). For example 3↑mat returns the first 3 rows of mat, and 3↓mat removes the first 3 rows.
https://help.dyalog.com/13.0/index.html?page=html%2Frelnotes13.0%2Fv13.0%20takedropindex.htm Jay. On Fri, 24 Apr 2020 at 23:03, Kacper Gutowski <mwgam...@gmail.com> wrote: > 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?) > >
