Serialize to JSON through a visitor

[kddnewton]

For posterity - most of this was generated through a script and then checked. The gist of the script is below:

#!/usr/bin/env ruby
# frozen_string_literal: true

require "bundler/setup"
require "syntax_tree"

program = SyntaxTree.parse(SyntaxTree.read(File.expand_path("../lib/syntax_tree/node.rb", __dir__)))
program => {
  statements: {
    body: [
      *,
      SyntaxTree::ModuleDeclaration[bodystmt: {
        statements: {
          body: [
            *,
            SyntaxTree::ClassDeclaration[
              constant: { constant: { value: ^(ARGV.first) } },
              bodystmt: { statements: { body: } }
            ],
            *
          ]
        }
      }]
    ]
  }
}

body => [*, SyntaxTree::Def[name: { value: "accept" }, bodystmt: { statements: { body: [SyntaxTree::Call[message: { value: visit_method_name }]] } }], *]
body => [*, SyntaxTree::Def[name: { value: "to_json"}, bodystmt: { statements: { body: [SyntaxTree::Call[receiver: SyntaxTree::HashLiteral => hash_literal]] } }] => method, *]

output = StringIO.new
output.puts("def #{visit_method_name}(node) {")

hash_literal.assocs.each do |assoc|
  output.print("#{assoc.key.value} ")

  case assoc.value
  in SyntaxTree::SymbolLiteral
    output.print(":#{assoc.value.value.value}")
  in SyntaxTree::VCall[value: { value: "location" }]
    output.print("visit_location(node.location)")
  in SyntaxTree::VCall[value: { value: "comments" }]
    output.print("visit_all(node.comments)")
  in SyntaxTree::VCall[value: { value: }]
    output.print("visit(node.#{value})")
  end

  output.puts(",")
end

output.puts("} end")
puts SyntaxTree.format(output.string)