BNF

Q1: Grouping and Pipes

In this question, you will add support for grouping and piping.

Recall that grouping allows for an entire regular expression to be treated as a single unit, and piping allows for a pattern to match an expression on either side. Combined, these will let us create patterns which match multiple strings!

Define the group and pipe expressions in your grammar.

1. A group consists of any regex expression surrounded by parentheses (()).
2. A pipe operator consists of a regex expression, followed by a pipe (|) character, and lastly followed by another regex expression.

For example, r"apples" would match exactly the phrase “apples” in an input. If we wanted our pattern from before to match “oranges” as well, we could expand our rstring to do so using groupings and pipes: r"(apples)|(oranges)".

Regular Expressions

Q1: Calculator Ops

Write a regular expression that parses strings written in the 61A Calculator language and returns any expressions which have two numeric operands, leaving out the parentheses around them.

写一个符合 (operand operator1 operator2) 格式的正则表达式. 这个是比较简单的, 因为这里的运算符只有 +, -, *, /. 我们用 [] 括起来就可以, 但是要注意**- 需要用 \ 转义**

Q2: Roman Numerals

Write a regular expression that finds any string of letters that resemble a Roman numeral and aren’t part of another word. A Roman numeral is made up of the letters I, V, X, L, C, D, M and is at least one letter long.

For the purposes of this problem, don’t worry about whether or not a Roman numeral is valid. For example, “VIIIII” is not a Roman numeral, but it is fine if your regex matches it.

Context

Problem 1

Important: Your code for this part should go in buffer.py.

Your job in this part is to implement the current and pop_first methods of the Buffer class.

current should return the current token of the current line we’re on in the Buffer instance without removing it. If there are no more tokens in the current line, then current should move onto the next valid line, and return the first token of this line. If there are no more tokens left to return from the entire source (we’ve reached the end of all input lines), then current should return None (this logic is already provided for you in the except StopIteration block).

Q1: My Filter

Write a procedure my-filter, which takes a predicate func and a list lst, and returns a new list containing only elements of the list that satisfy the predicate. The output should contain the elements in the same order that they appeared in the original list.

Note: Make sure that you are not just calling the built-in filter function in Scheme - we are asking you to re-implement this!

OOP

Q1: Vending Machine

In this question you’ll create a vending machine that only outputs a single product and provides change when needed.

Create a class called VendingMachine that represents a vending machine for some product. A VendingMachineobject returns strings describing its interactions. Remember to match exactly the strings in the doctests – including punctuation and spacing!

Fill in the VendingMachine class, adding attributes and methods as appropriate, such that its behavior matches the following doctests: