def _to_rpn(exp: Expression) -> Expression:
"""Parses expression to rpn format"""
queue = []
stack = []
for tok in exp:
# skips whitespaces
if tok.type is TokenType.WHITESPACE:
continue
# any variable or constant -> to queue
if tok.type in [TokenType.IDENTIFIER, TokenType.CONSTANT]:
queue.append(tok)
continue
# opening bracket -> to stack
if tok.type is TokenType.OPENING_BRACKET:
stack.append(tok)
continue
# closing bracket -> move form stack to queue
if tok.type is TokenType.CLOSING_BRACKET:
while stack[-1].type is not TokenType.OPENING_BRACKET:
queue.append(stack.pop())
stack.pop()
continue
# operators -> complicated xD
if tok.type in [TokenType.DOUBLE_OPERATOR, TokenType.SINGLE_OPERATOR]:
while len(stack) > 0 and stack[
-1].type is not TokenType.OPENING_BRACKET and (
stack[-1].precedence > tok.precedence or
(stack[-1].precedence == tok.precedence
and stack[-1].type is TokenType.SINGLE_OPERATOR)):
queue.append(stack.pop())
stack.append(tok)
continue
# other -> error
raise SyntaxException(tok, "Unexpected token")
# move everything from stack to queue
while len(stack) > 0:
queue.append(stack.pop())
# return queue - expression in rpn format
return queue
def check_syntax(exp: Expression):
"""Checks syntax of given expression and throws SyntaxExceptions if needed"""
indent = 0
state = 1
# for every token
for tok in exp:
# skips whitespaces
if tok.type is TokenType.WHITESPACE:
continue
# if in state 1
if state == 1:
# identifier -> ok, state 2
if tok.type is TokenType.IDENTIFIER:
state = 2
# opening bracket -> ok, state 1
elif tok.type is TokenType.OPENING_BRACKET:
indent += 1
state = 1
# single operator -> ok, state 1
elif tok.type is TokenType.SINGLE_OPERATOR:
state = 1
# constatnt -> ok, state 2
elif tok.type is TokenType.CONSTANT:
state = 2
# anything else -> error
else:
raise SyntaxException(tok, "Unexpected token")
# if in state 2
else:
# closing bracket -> check indentation, state 2
if tok.type is TokenType.CLOSING_BRACKET:
indent -= 1
state = 2
if indent < 0:
raise SyntaxException(tok, "Unexpected closing bracket")
# double operator -> ok, state 1
elif tok.type is TokenType.DOUBLE_OPERATOR:
state = 1
# anything else -> error
else:
raise SyntaxException(tok, "Unexpected token")
# checks final indentation
if indent != 0:
raise SyntaxException(exp[-1], "Missing closing bracket")
# checks final state
if state != 2:
raise SyntaxException(exp[-1], "Unexpected end of statement")