Lec28-Calculator

2024-10-21 133 words One minute

Contents

Calculator

Exception

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raise Exception("Invalid input")

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try:
    # code that may raise an exception
except Exception as e:
    print(e)

见java try-catch 😏

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float('inf') # positive infinity
float('-inf') # negative infinity

Programming Languages

Programs are trees… and the way interpreters work is through a tree recursion.

Parsing

把文本转化为抽象语法树（Abstract Syntax Tree，AST）

base case: only symbols and numbers

recursive case: expressions and statements

Scheme-Syntax Calculator

using Python Pair to describe pairs of expressions and statements

the eval function

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def calc_apply(op, args):
    """
    args: Iterable
    """
    if op == '+':
        ...
    elif op == '-':
        ...
    elif op == '*':
        ...
    elif op == '/':
        ...
    else:
        raise Exception("Invalid operator")

interactive cli

Read-Eval-Print-Loop (REPL) 😮