华为笔试9月20日100+100+90

机试前两题不难，第三题坑好多，最后也没AK

做了个比较简洁的实现，用python的locals()+eval()，其实可以很好处理加减乘除。

import sys
d = locals()
for line in sys.stdin:
    line = line.strip().replace("/", "//")
    if line.startswith("let"):
        try:
            name, expr = line[4:].split(" = ")
            # d[name] = eval(expr)
            l = expr.split()
            while len(l) > 2:
                x = eval(" ".join(l[:3]))
                l = [str(x)] + l[3:]
            if not name.isidentifier() or len(l) != 1:
                raise SyntaxError
            d[name] = int(l[0])
        except NameError:
            d[name] = "UNDEF"
        except:
            print("<syntax-error>")
    elif line.startswith("out"):
        name = line[4:-1]
        if not name.isidentifier():
            print("<syntax-error>")
        elif name not in d or d[name] == "UNDEF":
            print("<undefined>")
        elif d[name] < -2147483648:
            print("<underflow>")
        elif d[name] > 2147483647:
            print("<overflow>")
        else:
            print(d[name])
    else:
        print("<syntax-error>")