Imagine a language: wires

In jsonic, we saw how we could make a simple but useful DSL in under 50 lines of code. If anyone thought that creating a DSL was auto­mat­i­cally a giant under­taking—Racket makes it easy.

In turn, when DSLs are easy to make, they become a prac­tical option for solving a larger set of program­ming prob­lems—even small ones. In this tuto­rial, we’ll take that prin­ciple to its extreme. We’ll make a language called wires that’s designed to be used once and discarded.

And let’s cleanse the rice-cake flavor of JSON from our palate with some­thing more enter­taining.

The puzzle

This year, little Bobby Tables got a set of wires and bitwise logic gates! Unfor­tu­nately, little Bobby is under the recom­mended age range, and he needs help assem­bling the circuit.

Each wire has an iden­ti­fier (some lower­case letters) and can carry a 16-bit signal (a number from 0 to 65535). A signal is provided to each wire by a gate, another wire, or some specific value. Each wire can only get a signal from one source, but can provide its signal to multiple desti­na­tions. A gate provides no signal until all of its inputs have a signal.

The included instruc­tion booklet describes how to connect the parts:

For example, here’s a simple circuit:

After it’s run, these are the signals on the wires:

The ques­tion

The instruc­tion booklet for the circuit kit provides a descrip­tion of a circuit (which will be our puzzle input).

We have to deter­mine: What signal ends up on wire a?

Of course, we’re going to answer this ques­tion by making a DSL called wires.