assert ← {⍺←'assertion failure' ⋄ 0∊⍵:⍺ ⎕signal 8 ⋄ shy←0}

   assert 4 = 2+2

   assert 0 = 1+*○0j1 

   assert 'up' ≡ 'down'
assertion failure
   assert'up'≡'down'
  ∧