Class: Theta::Parser

Inherits:
Object
  • Object
show all
Defined in:
lib/theta/parser.rb

Overview

parses strings into arrays of items understandable by the interpreter

Instance Method Summary collapse

Instance Method Details

#atom(token) ⇒ Object

returns appropriate numeric object if a number, otherwise returns a symbol



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# File 'lib/theta/parser.rb', line 115

def atom(token)
  if token.start_with?("\"")
    return token.gsub("\"", "")
  end
  token.gsub!(/\n\t/, "")
  begin
    return Integer(token)
  rescue ArgumentError
    begin
      return Float(token)
    rescue ArgumentError
      return token.to_sym
    end
  end
end

#parse(string) ⇒ Object

returns the scheme interpretation of the string



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# File 'lib/theta/parser.rb', line 6

def parse(string)
  return read_from(tokenize(string))
end

#read_from(tokens) ⇒ Object

reads an expression from an array of tokens (created by tokenize)



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# File 'lib/theta/parser.rb', line 71

def read_from(tokens)
  if tokens.length == 0
    raise SyntaxError, "unexpected EOF while reading"
  end
  tokens.delete_if { |item| item.strip == "" || item == []}
  tmp, expression = restructure tokens
  return expression
end

#restructure(token_array, offset = 0) ⇒ Object 



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# File 'lib/theta/parser.rb', line 80

def restructure(token_array, offset = 0)
  statement = []
  while offset < token_array.length
    if token_array[offset] == "("
      offset, tmp_array = restructure(token_array, offset + 1)
      statement << tmp_array
    elsif token_array[offset] == ")"
      break
    else
      statement << atom(token_array[offset])
    end
    offset += 1
  end
  return offset, statement
end

#to_string(expression) ⇒ Object

convert an expression back to a readable string



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# File 'lib/theta/parser.rb', line 132

def to_string(expression)
  if expression.is_a? Array
    expression.map { |exp| to_string(exp) }
    return "(" + expression.join(" ") + ")"
  else
    return expression.to_s
  end
end

#tokenize(string) ⇒ Object

converts a string into an array of tokens



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# File 'lib/theta/parser.rb', line 11

def tokenize(string)
  tokens = []
  found_string = false
  temp = ""
  # loop through each character passed

  string.each_char do |char|
    # if we're currently in a string and we hit the quote,

    # it's the end of the string.

    # move the string into the token array

    if found_string
      if char == "\""
        found_string = false
        temp << char
        if not temp.empty?
          tokens << temp
        end
        temp = ""
      # otherwise add the character to the temporary variable

      else
        temp << char
      end
    else
      # if we hit parentheses, add whatever's in temp as a token

      # then add the parentheses as a token

      if char == "(" || char == ")"
        if not temp.empty?
          tokens << temp
          temp = ""
        end
        tokens << char
        next
      # if we hit a quote, we're beginning a string

      # flip the found_string flag and begin adding to the temp variable

      elsif char == "\""
        found_string = true
        temp << char
      # space signals the end of a token, push the temp variable on the token queue

      elsif char == " "
        if not temp.empty?
          tokens << temp
        end
        temp = ""
      # ignore tabs or newlines, unless there's something in temp

      # push that onto tokens

      elsif char == "\t" || char == "\n"
        if not temp.empty?            
          tokens << temp
        end
        temp = ""
      # add the character to temp to build a token

      else
        temp << char
      end
    end
  end
  return tokens
end