string = """
<% y = ["a", "b", "c"] %>
<%= with list when is_list(list) <- y do %>
  list
<% else _ -> nil %>
<% end %>
"""

result = EEx.eval_string(string, [], engine: EEx.Engine)
IO.inspect(result)

# ** (SyntaxError) nofile:4: syntax error before: else
#   lib/eex/compiler.ex:45: EEx.Compiler.generate_buffer/4
#   lib/eex/compiler.ex:54: EEx.Compiler.generate_buffer/4
#   lib/eex.ex:197: EEx.eval_string/3
#   foo.exs:9: (file)