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interpreter.py
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interpreter.py 4.03 KiB
import lexer
loop_program = '''x1 := 2;
x2 := 3;
x3 := x2 + 0;
LOOP x1 DO
x2 := x3 + 1;
x3 := x2 + 0
END;
x0 := x2 + 0'''
def process_assignment(token_queue, position, value_list, forbidden_identifiers):
identifier_1 = token_queue[position].v
if identifier_1 in forbidden_identifiers:
raise Exception("Identifier " + identifier_1 + "ist bereits in Loop vorhanden und darf nicht verwendet werden.")
if not token_queue[position + 1].k == 'EQUALS':
raise SyntaxError(":= in Zuweisung erwartet.")
if identifier_1 in value_list:
value_1 = value_list.get(identifier_1)
else:
value_1 = 0
if token_queue[position + 2].k == 'NUMBER':
value_1 += int(token_queue[position + 2].v)
value_list.update({identifier_1: value_1})
return position+3, value_list
if not token_queue[position + 2].k == 'IDENTIFIER':
raise SyntaxError("IDENTIFIER in Zuweisung erwartet.")
identifier_2 = token_queue[position + 2].v
if identifier_2 in forbidden_identifiers:
raise Exception("Identifier " + identifier_2 + " ist bereits in Loop vorhanden und darf nicht verwendet werden.")
if identifier_2 in value_list:
value_2 = value_list.get(identifier_2)
else:
value_2 = 0
if not token_queue[position + 4].k == 'NUMBER':
raise SyntaxError("NUMBER in Zuweisung erwartet.")
if token_queue[position + 3].k == 'PLUS':
value_1 = value_2 + int(token_queue[position + 4].v)
elif token_queue[position + 3].k == 'MINUS':
value_1 = max(0, value_2 + token_queue[position + 4].v)
else:
raise SyntaxError("PLUS oder MINUS in Zuweisung erwartet.")
value_list.update({identifier_1: value_1})
return position + 5, value_list
def process_loop(token_queue, position, value_list, forbidden_identifiers):
identifier_token = token_queue[position+1]
if not identifier_token.k == 'IDENTIFIER':
raise SyntaxError('IDENTIFIER in LOOP erwartet.')
if not token_queue[position+2].k == 'DO':
raise SyntaxError('DO in LOOP erwartet.')
number_of_loops = int(value_list.get(identifier_token.v))
saved_position = position + 3
forbidden_identifiers.append(identifier_token.v)
for index in range(number_of_loops):
position = saved_position
end_found = False
while(not end_found):
position, value_list = process_program(token_queue, position, value_list, forbidden_identifiers)
if token_queue[position].k == 'SEMICOLON':
position = position + 1
continue
elif token_queue[position].k == 'END':
end_found = True
else: raise SyntaxError("SEMICOLON oder END erwartet.")
return position+1, value_list
def process_program(token_queue, position, value_list, forbidden_identifiers):
current_key = token_queue[position].k
if current_key == 'IDENTIFIER':
try:
current_position, values = process_assignment(token_queue, position, value_list, forbidden_identifiers)
except IndexError:
raise Exception("Frühzeitiges Ende einer Zuweisung.")
elif current_key == 'LOOP':
try:
current_position, values = process_loop(token_queue, position, value_list, forbidden_identifiers)
except IndexError:
raise Exception("Frühzeitiges Ende eines LOOPs")
else:
raise SyntaxError("Keine passende Anweisung gefunden")
return current_position, values
def interpret(program):
tokens = lexer.tokenize(program)
current_position = 0
values = {}
forbidden_identifiers = []
while current_position < len(tokens):
current_position, values = process_program(tokens, current_position, values, forbidden_identifiers)
if current_position < len(tokens) and not tokens[current_position].k == 'SEMICOLON':
raise SyntaxError("Semicolon erwartet")
else:
current_position = current_position + 1
if "x0" in values:
return values.get("x0")
return 0
print(interpret(loop_program))