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