Double Recursion in Ruby

Question

I am trying to parse a nested array of Symbols into HTML my input is:

[[:html,
  [:head, [:title, "Hello World"]],
  [:body, [:h1, "Hello World"], [:p, "This is your parser"]]]]

My intended Output is:

<html>
  <head>
    <title>Hello World</title>
  </head>
  <body>
    <h1> Hello World </h1>
    <p> This is your parser</p>
  </body>
</html>

My Method is:

def to_html(data)
 if( data.is_a?(Array))

   open_map = data.map do |item|
    if( item.is_a?(Array))
      to_html(item)
    else
      if( item.is_a?(Symbol))
        "<"+ item.to_s + ">"
      else
        item.to_s
      end
    end
  end

  close_map = data.map do |item|
    if( item.is_a?(Array))
      to_html(item)
    else
      if( item.is_a?(Symbol))
        "</"+ item.to_s + ">"
      end
    end
  end
      open_map.join(' ')   + close_map.join(' ')
  else
    data.to_s
  end
end

This basically works except that it recurses too much in that I think the two recursive calls to to_html results in double output

ie:

<html> 
 <head>
   <title> Hello World
   </title>
 </head> 
   <title> Hello World
  </title>
<body>
. . . .

and so on

I think I need to nest the recursions or else filter the results

How can I fix this?

I think your input have one extra layer of []

Fabricator
– Fabricator

2014-07-29 22:16:21 +00:00
Commented Jul 29, 2014 at 22:16 — Fabricator
– Fabricator, Commented Jul 29, 2014 at 22:16

Fabricator · Accepted Answer · 2014-07-30 00:45:30Z

2

If you assume the first element of each array is the tag name, then it can be simplified to:

def to_html(data)
  if (data.is_a?(Array))
    tag = data[0]
    children = data[1..-1]
    return "<#{tag}>" + children.map {|x| to_html(x)}.join(' ') + "</#{tag}>"
  else
    return data
  end
end

print to_html([:html,
               [:head, [:title, "Hello World"]],
               [:body, [:h1, "Hello World"], [:p, "This is your parser"]]])

prints

<html><head><title>Hello World</title></head> <body><h1>Hello World</h1> <p>This is your parser</p></body></html>

edited Jul 30, 2014 at 0:45

answered Jul 29, 2014 at 22:17

Fabricator

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3 Comments

tbrooke Over a year ago

The Array is a tree of nested arrays of symbols so it has has to recurse into each array and convert the item to a string the surround the item with < >

Fabricator Over a year ago

@tbrooke, it does recursively print each tag (see updated answer with output). However, the input does not have the outer array as your sample input.

tbrooke Over a year ago

You are correct the extra layer came from the output of a parser that feed this function - I pulled it out and this works fine Thank You

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