def calc(text: str):
"""Read and evaluate a single line formula."""
try:
tokens = lex.TokenStream(io.StringIO(text))
stack = []
while tokens.has_more():
tok = tokens.take()
if tok.kind == lex.TokenCat.INT:
stack.append(expr.IntConst(int(tok.value)))
elif tok.kind == lex.TokenCat.PLUS:
right = stack.pop()
left = stack.pop()
stack.append(expr.Plus(left, right))
except lex.LexicalError as e:
print(f"*** Lexical error {e}")
return
except IndexError:
# Stack underflow means the expression was imbalanced
print(f"*** Imbalanced RPN expression, missing operand at {tok.value}")
return
if len(stack) == 0:
print("(No expression)")
else:
# For a balanced expression there will be one Expr object
# on the stack, but if there are more we'll just print
# each of them
for exp in stack:
print(f"{exp} => {exp.eval()}")
def expr(self, node) -> expr.Expr:
# if node is None:
# return expr.UnspecifiedExpr()
# else:
# #print('NODE', node, self.datum(node))
# return self.datum(node).expr(self, node)
#HACK Should do this by inheritance, but it's pretty readable
#having it all here.
if self.is_of_class(node, 'Plus'):
return expr.Plus(*(self.expr(rand)
for rand in self.neighbors(node, 'operands')))
elif self.is_of_class(node, 'Minus'):
return expr.Minus(self.neighbor(node, 'minuend'),
self.neighbor(node, 'subtrahend'))
elif self.is_of_class(node, 'Times'):
return expr.Times(*(self.expr(rand)
for rand in self.neighbors(node, 'operands')))
#TODO Div
elif self.is_of_class(node, 'Block'):
return self.expr(self.neighbor(node, 'source'))
elif self.is_of_class(node, 'Number'):
return expr.Number(self.value_of(node))
else:
return expr.UnspecifiedExpr()