Minimal interpreter for Brainfuck, written in Python. Doesn't make use of any AST, parses and interprets the code at the same time.

brainfuck.py

code = "++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++."
position = 0

memory = {}
pointer = 0

def getPointerValue():
	try:
		return memory[pointer]
	except:
		return 0

while position < len(code):
	char = code[position]
	if char == ">":
		pointer += 1
	elif char == "<":
		pointer -= 1
	elif char == "+":
		memory[pointer] = getPointerValue() + 1
	elif char == "-":
		memory[pointer] = getPointerValue() - 1
	elif char == ".":
		print(chr(getPointerValue()), end="")
	elif char == ",":
		memory[pointer] = ord(input("The program asks for input: ")[0])
	elif char == "[":
		if getPointerValue() == 0:
			position += 1
			endsToIgnore = 0
			while position < len(code):
				char = code[position]
				if char == "[":
					endsToIgnore += 1
				elif char == "]":
					if endsToIgnore > 0:
						endsToIgnore -= 1
					else:
						break

				position += 1
	elif char == "]":
		if getPointerValue() != 0:
			position -= 1
			startsToIgnore = 0
			while position > 0:
				char = code[position]
				if char == "]":
					startsToIgnore += 1
				elif char == "[":
					if startsToIgnore > 0:
						startsToIgnore -= 1
					else:
						position -= 1
						break

				position -= 1

	position += 1