Better error message for lambda validation

[mslinn]

I want to verify that the provided answer is within the range of allowable string lengths (min..max). This was my first attempt:

value = @prompt.ask(msg, value: value) do |q|
  q.required true
  q.validate ->(v) { return v.length >= min && v.length <= max }
end

When the input is not within the range of min characters to max characters in length, the error message is: The answer is invalid (must match #<Proc:0x00007f395836e410 /jekyll-new_post/lib/jekyll/new_post.rb:131 (lambda)>). That is a horrible error message.

Next, I tried to write the following, but found I was unable to access the current answer while preparing q.messages[:valid?]:

value = @prompt.ask(msg, value: value) do |q|
  q.required true
  q.messages[:valid?] = check_length(min, max, ????) # Is there some way to pass the current answer to `check_length`?
  q.validate ->(v) { return v.length >= min && v.length <= max }
end

def check_length(min, max, string)
  length = string.length
  if length < min
    "#{min - length} characters too short, please edit"
  elsif length > max
    "#{length - max} characters too long, please edit"
  else
    "#{length} characters, excellent!"
  end
end

Is there some way to use q.messages[:valid] so that a better error message can be provided? If not, is there a way to invoke q.validate to avoid the horrible message shown?