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B. Wilson
B. Wilson
06:25
@Adám Here's an interesting approach to system-wide APL input: github.com/secwang/espanso-apl-keyboard
 
3 hours later…
Johannes Hoff
Johannes Hoff
09:38
Thanks, Paul. Enclosing was what I needed. I still need to build up my intuition for strings not being strings :)
B. Wilson
B. Wilson
10:29
'foo' 'bar' 'foo' 'baz'∊⊂'foo'
@JohannesHoff Careful about the semantics of ⍷. It looks for places where the entire argument on the left occurs as a subarray within the right argument.
My example above gets what (I believe) you want, but at first blush it does seem to be using ∊ backwards. The key is that ∊ returns true/false for every item on the left, which gives us what we want when the right argument is a single item.
But since strings in APL are character vectors and not single items, we need the ⊂.
Johannes Hoff
Johannes Hoff
10:50
Hm. That does indeed work, but in this case has an equivalent expression with ⍷. Not sure I see which one is "right"

'foo' 'bar' 'foo' 'baz'∊⊂'foo'
┌→──────┐
│1 0 1 0│
└~──────┘
(⊂'foo')⍷'foo' 'bar' 'foo' 'baz'
┌→──────┐
│1 0 1 0│
└~──────┘
B. Wilson
B. Wilson
11:01
Specializing to strings, you can think of ⍷ as looking for substrings: 
      ⍸'foo'⍷'foo bar foo baz'
0 8
So the 0th and 8th positions mark where 'foo' begins in the right hand side.
However, if your left argument is just a single character, then it's sort of an edge case where the string start and end are the same.
The same applies if you generalize from strings to vectors of strings, like in your example with ⍷.
Since ⍷ is a "substring search" it's more of a heavyweight option.
Generally, if you're just looking for items matching other items, then you'll want to reach for ∊, ⍳ and the like.
Johannes Hoff
Johannes Hoff
Thanks! I'll use ∊ now, then
 
6 hours later…
Adám
Adám
17:04
@B.Wilson Ah, right, I remember that, but I don't remember why we didn't just go with that. Will take it up with Rich.
@JohannesHoff It may be easier to understand≡¨ as in (⊂'foo')≡¨'foo' 'bar' 'foo' 'baz' or 'foo' 'bar' 'foo' 'baz'≡¨⊂'foo' (they are equivalent).

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