apl: primes sieve (2=+⌿0=A∘.|A)/A←⍳N + apl-compress (+11 tests, 280/280)

lib/apl/tests/programs/primes.apl

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+⍝ Sieve of Eratosthenes — the classic APL one-liner
+⍝   primes ← (2=+⌿0=A∘.|A)/A←⍳N
+⍝
+⍝ Read right-to-left:
+⍝   A ← ⍳N        : A is 1..N
+⍝   A∘.|A         : outer-product residue table — M[i,j] = A[j] mod A[i]
+⍝   0=...         : boolean — true where A[i] divides A[j]
+⍝   +⌿...         : column sums — count of divisors per A[j]
+⍝   2=...         : true for numbers with exactly 2 divisors (1 and self) → primes
+⍝   .../A         : compress — select A[j] where mask[j] is true
+⍝
+⍝ Examples:
+⍝   primes 10  →  2 3 5 7
+⍝   primes 30  →  2 3 5 7 11 13 17 19 23 29
+
+primes ← {(2=+⌿0=⍵∘.|⍵)/⍵←⍳⍵}