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JSON parser with pattern matching
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| require "json" | |
| struct = { "a" => 1, "b" => 2, "c" => [1, 2, 3], "d" => [{ "e" => 3 }, nil, false, true, [], {}] } | |
| source = JSON.dump(struct) | |
| tokens = [] | |
| index = 0 | |
| until source.empty? | |
| tokens << | |
| case source.strip | |
| when /\A[\{\}\[\],:]/ then $&.to_sym | |
| when /\A(\d+)/ then $1.to_i | |
| when /\A"([^"]*?)"/ then $1 | |
| when /\A(true|false)/ then $1 == "true" | |
| when /\Anull/ then nil | |
| else raise | |
| end | |
| source = $' | |
| end | |
| def parse_array(tokens) | |
| result = [] | |
| loop do | |
| item, tokens = parse_item(tokens) | |
| result << item | |
| case tokens | |
| in [:"]", *rest] then return result, rest | |
| in [:",", *rest] then tokens = rest | |
| end | |
| end | |
| end | |
| def parse_object(tokens) | |
| result = {} | |
| loop do | |
| tokens => [String => key, :":", *tokens] | |
| value, tokens = parse_item(tokens) | |
| result[key] = value | |
| case tokens | |
| in [:"}", *rest] then return result, rest | |
| in [:",", *rest] then tokens = rest | |
| end | |
| end | |
| end | |
| def parse_item(tokens) | |
| case tokens | |
| in [:"[", :"]", *rest] then [[], rest] | |
| in [:"[", *rest] then parse_array(rest) | |
| in [:"{", :"}", *rest] then [{}, rest] | |
| in [:"{", *rest] then parse_object(rest) | |
| in [FalseClass | Integer | NilClass | String | TrueClass => value, *rest] | |
| [value, rest] | |
| end | |
| end | |
| def parse(tokens) | |
| parse_item(tokens) => [value, []] | |
| value | |
| end | |
| p struct | |
| p parse(tokens) |
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