RGS's solution for Problem 2, Phase 2 of 2020 APL competition (see https://mathspp.com/blog/2020-apl-competition for my thoughts on it)

P2Phase2_2020.dyalog

Steps ← {
    (⎕IO ⎕ML ⎕WX) ← 0 1 3
    ⍝ Utility function to generate ranges of numbers.
    ⍝ Dyadic function expecting a number on the left (mode) and a 2-element number vector (s f) on the right (steps start and end points).  
    ⍝  - if ⍺ is negative, return vector with |⌊⍺ equally-sized steps from s to f.
    ⍝  - if ⍺ is positive, ⍺ represents the step size.
    ⍝  - if ⍺ is 0, return s
    ⍝ Returns a vector of numbers between s and f.
    ⍺ ← 1
    (s f) ← ⍵
    r ← f-s
    ⍝⍺<0:⍵ ∇⍨(f-s)÷|⌊⍺  ⍝ clever but fails the ¯4 Steps 42 42 test case
    ⍺<0: s + (⎕IO-⍨⍳st+1) × (r) ÷ st←|⌊⍺
    ⍺=0: s
    ⍺>0: f ,⍨ s+(×r)×⍺×⎕IO -⍨ ⍳⌈|r÷⍺
}