```ruby
require 'smartdown/model/flow'
require 'smartdown/parser/node_interpreter'
require 'smartdown/parser/snippet_pre_parser'

module Smartdown
  module Parser
    class ParseError < StandardError
      attr_reader :filename, :parse_error

      def initialize(filename, parse_error)
        @filename = filename
        @parse_error = parse_error
      end

      def to_s(full = true)
        "Parse error in '#{filename}':\n\n" + @parse_error.cause.ascii_tree
      end
    end

    class FlowInterpreter
      attr_reader :flow_input

      def initialize(flow_input)
        @flow_input = pre_parse(flow_input)
      end

      def interpret
        Smartdown::Model::Flow.new(coversheet.name, [coversheet] + questions + outcomes)
      end

    private
      def coversheet
        interpret_node(flow_input.coversheet)
      end

      def questions
        flow_input.questions.map { |question_data| interpret_node(question_data) }
      end

      def outcomes
        flow_input.outcomes.map { |outcome_data| interpret_node(outcome_data) }
      end

      def interpret_node(input_data)
        Smartdown::Parser::NodeInterpreter.new(input_data.name, input_data.read).interpret
      rescue Parslet::ParseFailed => error
        raise ParseError.new(input_data.to_s, error)
      end

      def pre_parse(flow_input)
        SnippetPreParser.parse(flow_input)
      end
    end
  end
end
```

Use input data filename rather for ParseError message
user
```ruby
require 'smartdown/model/flow'
require 'smartdown/parser/node_interpreter'
require 'smartdown/parser/snippet_pre_parser'

module Smartdown
  module Parser
    class ParseError < StandardError
      attr_reader :filename, :parse_error

      def initialize(filename, parse_error)
        @filename = filename
        @parse_error = parse_error
      end

      def to_s(full = true)
        "Parse error in '#{filename}':\n\n" + @parse_error.cause.ascii_tree
      end
    end

    class FlowInterpreter
      attr_reader :flow_input

      def initialize(flow_input)
        @flow_input = pre_parse(flow_input)
      end

      def interpret
        Smartdown::Model::Flow.new(coversheet.name, [coversheet] + questions + outcomes)
      end

    private
      def coversheet
        interpret_node(flow_input.coversheet)
      end

      def questions
        flow_input.questions.map { |question_data| interpret_node(question_data) }
      end

      def outcomes
        flow_input.outcomes.map { |outcome_data| interpret_node(outcome_data) }
      end

      def interpret_node(input_data)
        Smartdown::Parser::NodeInterpreter.new(input_data.name, input_data.read).interpret
      rescue Parslet::ParseFailed => error
        raise ParseError.new(input_data.name, error)
      end

      def pre_parse(flow_input)
        SnippetPreParser.parse(flow_input)
      end
    end
  end
end
```
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