typeof-lhs := λ(: lhs AST). (: (
   (let r TAny)
   (match lhs (
      ()
      ( (App( (Lit( ':_s _ )) (App( _ (AType tt) )) )) (
         (set r tt)
      ))
      ( (App( ps (App( (Lit( ':_s _ )) (App( _ (AType tt) )) )) )) (
         (set r (t3( 'Cons_s (typeof-lhs ps) tt )))
      ))
      ( ASTNil (
         (set r (t1 'Nil_s))
      ))
      ( _ (exit-error( 'Unknown\sLHS_s lhs )))
   ))
   r
) Type);