Avoid duplicate evaluations in chaining comparison

[yuanming-hu]

What's the behavior of 1 < ti.append(x, [], 1) < 10?

[archibate]

Behaves bad:

>>> 1 < 233 < 10
False

You may want to define a function, whose parameter holds temp value:

def between(a, x, b):
  return a < x and x < b

Or try ti.append(x, [], 1) in range(0, 10) if integer for elegence.

[yuanming-hu]

Yeah, call a function is a good solution as the result of ti.append is now passed by value instead of getting evaluated twice. Given that the chain can be rather long (e.g. a < b < c < d < e), it's better to modify the frontend compiler to cache the results of comparators:

taichi/python/taichi/lang/transformer.py

Line 533 in 0e5b3e5

def visit_Compare(self, node):

Assigning this to @xumingkuan since only a little bit of Python engineering is needed.

[yuanming-hu]

Well done by @xumingkuan. Closing.