Lab 18

# Lab 18 Instructions #

## Reminders #

• While students are coming into class, feel free to go ahead and download the lab materials in preparation for the start of the lab proper. (But please wait until you’re instructed before beginning work on the lab.)

• Get out paper and pencil. You’ll need it for this lab.

• For the upcoming labs, especially lab 19, we recommend downloading the repo early and looking over the files to get familiar with what you’ll be doing with your lab group in the labs sessions.

## Lab puzzle #

Here is the semantic rule ($R_{+}$) for the binary addition operator from Figure 19.4 (lexical environment semantics with environment and store):

Here are four variants of the rule:

Which if any of these rules provide the same semantics as the original rule? That is, which ones could we use instead of the original and still be able to derive exactly the same judgements? (Select all that apply (A-D))

(A) Variant A

(B) Variant B

(C) Variant C

(D) Variant D