Class: BfRb::Interpreter

Inherits:
Object
  • Object
show all
Defined in:
lib/bfrb/interpreter.rb

Overview

interprets brainfuck code

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Interpreter

initialize the interpreter



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# File 'lib/bfrb/interpreter.rb', line 11

def initialize
	@memory = Memory.new
	initialize_environment
	@input_stream = $stdin
	@output_stream = $stdout
end

Instance Attribute Details

#input_stream ⇒ Object

Returns the value of attribute input_stream.



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# File 'lib/bfrb/interpreter.rb', line 8

def input_stream
  @input_stream
end

#memory_counter ⇒ Object (readonly)

Returns the value of attribute memory_counter.



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# File 'lib/bfrb/interpreter.rb', line 7

def memory_counter
  @memory_counter
end

#output_stream ⇒ Object

Returns the value of attribute output_stream.



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# File 'lib/bfrb/interpreter.rb', line 8

def output_stream
  @output_stream
end

#program_counter ⇒ Object (readonly)

Returns the value of attribute program_counter.



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# File 'lib/bfrb/interpreter.rb', line 7

def program_counter
  @program_counter
end

Instance Method Details

#check_for_matching_braces ⇒ Object

checks the code to be run to make sure all braces match



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# File 'lib/bfrb/interpreter.rb', line 38

def check_for_matching_braces
	brace_counter = 0
	@code.each_char do |char|
		if char == "["
			brace_counter += 1
		elsif char == "]"
			brace_counter -= 1
			if brace_counter < 0
				@output_stream.puts "Unmatched ]"
				return false
			end
		end
	end
	if brace_counter > 0
		@output_stream.puts "Unmatched ["
		return false
	end
	return true
end

#current_memory ⇒ Object

returns the value in the current memory cell



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# File 'lib/bfrb/interpreter.rb', line 123

def current_memory
	return @memory.get(@memory_counter)
end

#evaluate_code ⇒ Object

evaluate each instruction in the current code



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# File 'lib/bfrb/interpreter.rb', line 59

def evaluate_code
	while ((0 <= @program_counter) and (@program_counter < @code.length))
		evaluate_instruction(@code[@program_counter])
	end
end

#evaluate_instruction(instruction) ⇒ Object

evaluate an individual instruction



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# File 'lib/bfrb/interpreter.rb', line 66

def evaluate_instruction(instruction)
	case instruction
	# shift right in memory
	when ">"
		@memory_counter += 1
	# shift left in memory, unless we're at the beginning
	when "<"
		if @memory_counter > 1
			@memory_counter -= 1
		else
			@memory_counter = 0
		end
	# increment value in memory
	when "+"
		@memory.set(@memory_counter, current_memory + 1)
	# decrement value in memory
	when "-"
		unless current_memory == 0
			@memory.set(@memory_counter, current_memory - 1)
		end
	# print value in memory
	when "."
		@output_stream.print current_memory.chr
	# input a character into memory
	when ","
		@output_stream.puts
		input = @input_stream.gets.getbyte(0)
		if input == 24
			throw :quit
		end
		@memory.set(@memory_counter, input)
	# jump to the closing bracket if memory is 0
	when "["
		if current_memory != 0
			@loop_stack.push @program_counter
		else
			bracket_counter = 1
			while ((bracket_counter != 0) and (@program_counter < @code.length - 1))
				@program_counter += 1
				if @code[@program_counter] == "["
					bracket_counter += 1
				elsif @code[@program_counter] == "]"
					bracket_counter -= 1
				end
			end
		end
	# return to the opening bracket if memory is not zero
	when "]"
		matching_bracket = @loop_stack.pop
		if current_memory != 0
			@program_counter = matching_bracket - 1
		end
	end
	@program_counter += 1
end

#initialize_environment ⇒ Object

cleans the memory and initializes member variables



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# File 'lib/bfrb/interpreter.rb', line 19

def initialize_environment
	@memory.clear
	@program_counter = 0
	@memory_counter = 0
	@code = ""
	@loop_stack = []
end

#run(code) ⇒ Object

run a given piece of code



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# File 'lib/bfrb/interpreter.rb', line 28

def run(code)
	@code += code.delete "^[]<>.,+-"
	if check_for_matching_braces
		catch :quit do
			evaluate_code
		end
	end
end