The particular question asks to find all palindrome numbers between 900 and 1000.
new_set ← (900 + ⍳100)
901, 902, 903, 904, ..., 999, 1000
⍕¨(new_set ∘.× new_set)
{⍵≡⌽⍵} ⍕¨(new_set ∘.× new_set)
The first line creates the new set of numbers.
The second line multiplies all numbers in new_set by every other number including itself. Creates a sort of outer product multiplication table, then converts the numbers into strings.
Last line attempts to find all palindromes, but fails and returns 0..
Any and all help is appreciated!
⍕¨(new_set ∘.× new_set) has shape 100 100, and Match (≡) compares entire arrays, so your final dfn there is comparing a 100 by 100 array against the Reverse (⌽) of the whole array.
What it looks like you're wanting is to reverse individual strings. Trying to copy your style, we get something like this:
{(⊃⍵)≡⌽⊃⍵}¨ ⊂∘⍕¨ (new_set ∘.× new_set)
Notice the double usage of Each (¨) and needing to Enclose (⊂) the strings just for the second Each and then immediately Disclose (⊃) in the dfn. This should probably feel dirty.
We can do better.
First, why not merge the two Each iterations?
{(⊃⍵)≡⌽⊃⍵}∘⊂∘⍕¨ (new_set ∘.× new_set)
But, in fact, Outer Product (∘.×) is already operating on exactly the items we want, so it make sense to just do everything there:
new_set ∘.{(⊢≡⌽)⍕⍺×⍵} new_set
N.B. Instead of repeating new_set on the left and right, it's probably more idiomatic to use Commute (⍨). I'll also throw in another spelling of (⊢≡⌽), just for fun:
∘.{≡∘⌽⍨⍕⍺×⍵}⍨ new_set
Turning this binary mask into the actual set of palindromes is pretty straightforward, so I'll not spoil that fun.